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What tubes to use with this Interstage Transformers?

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Posted on August 23, 2016 at 18:06:41
megasat16
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 I have a couple of interstage driver transformers and I want to hear opinions on the best possible driver and output tube combinations for the SET amps.

The IT is single Plate to Grid type with 10K Primary and 330K Secondary (nominal) with 20mA of permissible DC and 135V Rms Signal Max for the Primary Rating. FR is 20-20KHz with only +0.5dB and -0.5dB deviation from 1KHz during an actual sweep with Function Generator and a Scope.

Step Ratio is 1:4.

I am thinking to use 801A type as a driver with 18mA Plate Current to drive the Grid of Large (unknown / undecided) Transmitter tubes!

Suggestions Welcome!

Thanks Folks!
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RE: What tubes to use with this Interstage Transformers?, posted on August 23, 2016 at 21:08:27
Tre'
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 With a step up ratio of 1:4, the impedance ratio is 1:16

The Miller capacitance of the output tube will be increased 16 times as seen by the driver tube.

I can't see how that would be useful as a IT between the driver tube and the output tube.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on August 23, 2016 at 21:28:20
megasat16
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 Well, it is the driver transformer used to drive large Eimac tubes.

As far as IT is concerned, it's to load the driver tube properly while providing the signal coupling to the grid of the output?

Since it's not the output stage, how's the Miller C effecting the driver tube? The driver is properly biased and loaded at the optimal load which is the primary of the IT around 10K-15K which I think is what the 801A wants.
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You want a low anode impedence..?, posted on August 24, 2016 at 15:27:02
andy evans
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 if you're stepping up don't you want a lower anode impedence than the 801A?

4P1L is fairly low with a mu of around 11 so you get some gain.

Otherwise maybe a 2a3 at low current - never tried it....

I'd be looking for other solutions, like using a Gyrator with a DHT like Ale Moglia uses - see his site Bartola Valves. That way you get the gain and the low output impedence. He sells the gyrator boards. If you used one of those with a 4P1L it would be a great driver. You could then use your interstage in a preamp, in 4:1, if you wanted to find a use for it.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 24, 2016 at 18:11:06
Tre'
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 The reactance of the Miller capacitance of the output tube will be reflected back to the driver tube through the IT.

If the Miller capacitance of the output tube is 100pf (just picking a number here), it has a reactance at 100kHz of 15.9k ohms

If the IT has a impedance ratio of 1:16, that 15.9k ohms of reactance will be reflected back to the driver tube as 975 ohms of reactance, just as if the Miller capacitance value has been increased 16 times.

Once you know what output tube you are going to use, then you can calculate the requirements for the driver tube (output impedance and current delivery capability) that will allow you to use those ITs successfully.

As a side note; transformers don't have impedances per se. Different transformers are meant to work into different ranges of impedances and that has to do the the inductances and capacitances present in the transformer winding.

Transformers only have winding ratios.......but if we take a transformer meant to work in a circuit with a 15k impedance and try to to operate it in a circuit with only 1k of impedance, as an example, there will not be enough inductance to "support" a 1k reflected impedance. Going the other way causes problems as well.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on August 24, 2016 at 22:00:20
megasat16
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 So, the CMiller and the r at the Output tube is dependent upon the Frequency and it will make the frequency roll off somewhat problematic. It's also true the impedance from the output tube got reflected to the plate of the driver tube but as long as it's not very high, I don't see how it poses a problem.

In the case of the 801A, the data sheet suggest the 425V B+ at 18mA plate current will require about 10K ohm load resistance so if I load it with 10K-15K Primary of the IT, I think it should work fine. Would you otherwise thinking it will not work?

I just need to make sure the Secondary of the IT is connected to the overall Impedance of 160K or more if possible. Thus, the quest for the suitable output tube begins.

1:4 IT isn't a problem to drive the output tubes. I just need to find the right tubes. Tango has NC14 with 1+1:1+1 and you can wire it as (0.5:2) which is 1:4. NC14 have lower Primary load impedance though.


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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: You want a low anode impedence..?, posted on August 24, 2016 at 22:03:23
megasat16
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 Andy,

I have that thought too but I might end up with a couple of nice Preamp. I have saved a bit of those iron for various projects. And I am saving a few matched pairs of these IT with perfectly matched FR between the two so I might use them for the preamp stage.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 25, 2016 at 08:04:56
Tre'
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 "I just need to make sure the Secondary of the IT is connected to the overall Impedance of 160K or more if possible. Thus, the quest for the suitable output tube begins."

Using a 1:16 IT you will need an output tube with a very low Miller capacitance to meet that goal......like a pentode....I was assuming that because you are using a direct heated driver tube that you would be looking for a direct heated output tube.

Direct heated output tubes have very high Miller capacitances.


Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on August 25, 2016 at 10:57:21
megasat16
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 Thank you Tre! I appreciate your valuable input and I am now looking closely at the values for Grid to Plate C of the output tubes in my quest.

You are right that I am only looking to drive DHT output with DHT driver tube.

Thanks,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 27, 2016 at 06:11:21
dave slagle
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 I would really like to know what these IT's are since if the specs you publish are true, that is a pretty incredible engineering feat.

Getting a -0.5dB at 20hz in any inductive device to load a 10 (5K source impedance) is no small task to begin with since you need around 100hy's of primary inductance. Adding 18ma of unbalanced DC and accounting for the 135V of AC signal on top of it for the primary adds two more layers of complexity to the design, Now realizing that this is just for the primary and you now need to allocate a good part of the winding window to the secondary that requires 4-5X the turns of the primary and finally get flat response to 20Khz is amazing.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 27, 2016 at 09:54:31
megasat16
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 Hi Dave,

Per my first post, "FR is 20-20KHz with only +0.5dB and -0.5dB deviation from 1KHz during an actual sweep with Function Generator and a Scope."

I measured both an Open Load FR Sweep and 10K Resistive Load FR sweep using a Function Generator (21V output from 50ohms source impedance) and probe on 10X scale on my Hameg Scope. There isn't much change to the step ratio or FR for both measurements. I took 16-17 test data points and I sweep the entire AF band very slowly to see if there is any abrupt changes in the FR like a rise and fall and than rise again (interestingly, some very precious UTC iron did that even though only about 0.5 to 1dB change). These babies have pretty smooth FR all the way with -0.5dB and +0.5dB from the 1KHz Range. The entire difference is 1dB for 20-20KHz. I think it's pretty good for the IT given the Tango NC-14 has 2dB and NC-20 has 2dB but they have much higher rated DC on the Primary. Now, I don't know the Primary Inductance at 20Hz or 1KHz or 20KHz since I don't have an impedance analyzer yet. I am looking to get one. The Sencore LCR meter I have can only measure up to 20H.

The other SPEC is straight from printed label on the IT.

Anyway, I didn't hook it up to the DC bias on the primary so I don't know how it will perform when DC is applied on the Primary side.

Like the UTC H Series, they are sealed type for the Mil Communications Gears so the rule of thumb is that the quality far exceed that of the Audiophiles Standard. They have a 3dB bandwidth to about 100KHz. They were probably made by UTC too. Who knows?

Best Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 27, 2016 at 11:24:22
dave slagle
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 The 50 ohm source impedance explains a lot when it comes to the LF behavior. Before you get to far into this try inserting a 5K series resistor in series with the 50 ohm output of the signal generator to simulate the Rp of a 10.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 27, 2016 at 19:46:41
megasat16
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 Dave,

I can certainly try that. Is it to stimulate 5K source impedance so it's close to the ideal load impedance from the IT Primary?

Looking from the IT side, inserting a 5K (2 x 10K Resistor in Parallel) in series with the Input so the source impedance of 50 ohms before is now 5K resistive source with still 50ohms impedance drive at 20Hz.

But looking from the Signal Generator, the source impedance of it's own is still 50ohms (that is somewhat variable with frequency it's set at) and it is now driving a voltage divider of 5K series resistor which is in parallel with DCR plus the impedance of the Primary side of IT at 20Hz.

Max Current from SigGen supply to the IT is about 42mA (21Vp-p@20Hz / 5000ohms) but it need to drive the parallel load with (40-100ohms) DCR plus some reactive impedance of the primary of the IT side.

As far as I have learned, most Signal Generator are made to drive mostly resistive load or reactive load at much higher frequency than 20Hz. There are some shortcomings and stability at driving reactive at low frequency due the transmission line reflection.

Anyway, what I am saying is that the input signal to the IT will be highly distorted at 20Hz due to the reflective impedance back to the Signal Generator combined with it's own internal impedance at 20Hz.

That distortion is not due to the lack of inductance of the Transformer at 20Hz since there is no load connected to the IT yet (secondary side still open).

That distorted signal will somewhat recover when the frequency on the signal generator slowly rises (let's say 50Hz or more). It's again not due to the connected IT with the open secondary.

I have some other transformers with 50ohms primary and 15Kohms secondary (step ratio of 1:18) which I can cascade the IT for more FR sweeps.

Would it do what you want to do?

Thanks,
James



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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 07:19:46
dave slagle
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 Hey... I'll go line by line on this one... I understand this gets technical so those not interested can move along....

I can certainly try that. Is it to stimulate 5K source impedance so it's close to the ideal load impedance from the IT Primary?

No. The impedance numbers printed on a can come with all kinds of assumptions that are not always laid out for you so I prefer to ignore them and test for myself.

The 5K series resistor will simulate how the transformer will behave when driven by a 10 which is a possible real world application. Before you spend all kinds of time building the actual circuit on an "unknown" transformer it is wise to do a couple of preliminary tests to avoid any surprises down the road. (like falling response at 100hz)


But looking from the Signal Generator, the source impedance of it's own is still 50ohms (that is somewhat variable with frequency it's set at) and it is now driving a voltage divider of 5K series resistor which is in parallel with DCR plus the impedance of the Primary side of IT at 20Hz.

I find it to be a good approach to draw a line across the circuit (cut a wire if you will) and look forward and back to see the impedances involved. In the case of the 5K resistor in series with the output of the signal generator if you look downstream you have a 5K series resistance and whatever load it is connected to as the total load of the signal generator. Even if you drive a dead short, there is still a 5K load and if your signal generator has a problem with that.... get a new signal generator. Now that we have determined that the 5K additonal load actually helps the signal generator we can look at the actual source impedance driving our load (transformer).

Looking back from the transformer we have a 5K series resistance and a somewhat nonlinear output impedance of your signal generator. Even if the 50 ohms goes up to 500 ohms, the 5K series resistor is still going to dominate so again things are "better"

Max Current from SigGen supply to the IT is about 42mA (21Vp-p@20Hz / 5000ohms) but it need to drive the parallel load with (40-100ohms) DCR plus some reactive impedance of the primary of the IT side.

The DCR of a primary is in series with the inductance and both then appear in parallel with the reflected load. When looking at LF behavior, you do not need to add any loading so essentially you are just dealing with the primary inductance. With a 5K series resistor and 20V of AC you will limit the current provided by the signal genrator to 4ma even into a dead short.

As far as I have learned, most Signal Generator are made to drive mostly resistive load or reactive load at much higher frequency than 20Hz. There are some shortcomings and stability at driving reactive at low frequency due the transmission line reflection.

I don't think this comes into play with this type of measurement.

Anyway, what I am saying is that the input signal to the IT will be highly distorted at 20Hz due to the reflective impedance back to the Signal Generator combined with it's own internal impedance at 20Hz.

in this case the 5K series resistor to simulate the 10's Rp will eliminate that.

That distortion is not due to the lack of inductance of the Transformer at 20Hz since there is no load connected to the IT yet (secondary side still open).

the inductance is always there, the distortion you speak of is probably due to the inability of the generator to sink / supply enough current to deal with the reactive nature of the choke which requires double the current for every octave down you go in frequency.

That distorted signal will somewhat recover when the frequency on the signal generator slowly rises (let's say 50Hz or more). It's again not due to the connected IT with the open secondary.

I don't follow. the secondary load doesn't come into play here. If the primary is connected the inductance is connected and by the time any audio transformer loads down a signal generator you should be well beyond any frequency of interest. Measuring distortion at low frequency is a different animal altogether but this is just looking at amplitude response.

I have some other transformers with 50ohms primary and 15Kohms secondary (step ratio of 1:18) which I can cascade the IT for more FR sweeps.

Nooooo.... that may work well for the midband but it is the extremes you are interested so now you need to confirm that your "cascaded" transformer has 10X the bandwidth of the "tested" transformer with means 2hz to 200Khz just for the audio band and hopefully the behaviors we are looking at fall outside of the audio band so that second transformer essentially need DC to light bandwidth which interestingly enough that 5K series resistor almost has.


dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 09:36:28
Lenin
 Better do measurement for a SE transformer WITH the right dc, not only a ac measurement.

You can do it with a good ccs or even better with the tube you want to use for it.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 10:09:17
dave slagle
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 Obviously it is best to measure it in circuit but a few simple preliminary tests will let you know if it is worth looking deeper. If it doesn't have acceptable frequency response without DC, adding DC will not fix it.


It is entirely possible that the behavior is acceptable without DC and adding DC at some point will cause the primary inductance to drop and that behavior can be explored once a basic AC behavior is established.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 10:28:15
Lenin
 Just ac measurements can give bad low frequenty respons if there is to less signal. The gap helps a bit to prevent this but after all the right dc helps to get the right low frequency response. Permeability is then optimal.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 12:04:49
hifipaul
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 I have recently built a 300b amp with a UTC H series interstage of 1:2.5. It has been very problematic. A low impedance source is necessary, <900 ohms is a must. At that it still quits 2v before 0 bias, ie; it can't handle grid current. I still haven't solved the ringing problem.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 12:19:51
dave slagle
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 I have never seen the addition of DC increase permeability. I have seen random comments on how a "core needs the DC to turn it on" but think that is just an old wives' tale and have never been to replicate that type of behavior on the bench.

In a core with an unsecured gap, the addition of DC will "pull" the core together and decrease the size of the gap giving more inductance but this is simply an increase of effective permeabilty by the reduction of gap size and not a function of the "DC turning the core on"

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 12:52:20
Lenin
 We are talking about a SE transformer.

Normally permeability depends on exitation level and normally the maximum permeability is between 0,8T and 1,1T for HiB silicium steel.

If you have only ac sgnal and also a small signal signal then you have the possibility that you have to low permeability.
A good se transformer is designed in between 0,8 and 1,1 T in the area where permeability is high. But only with dc!

You can easely measure that with pp transformers or se without a dc that with small, smallers and the smallest signals the low frequencies become weaker and weaker.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 14:51:43
dave slagle
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 I think you are confusing AC permeability with DC magnetization.

If you have only ac signal and also a small signal signal then you have the possibility that you have to low permeability.

yes... but at no point will adding a DC to a small AC signal increase the permeability.

A good se transformer is designed in between 0,8 and 1,1 T in the area where permeability is high. But only with dc!

The typical numbers you state are for a transformer that carried DC current and it simply states to use about 1/2 the available flux for DC magnetization leaving the remaining half for ac excitation. It has nothing to do with permeability.

You can easely measure that with pp transformers or se without a dc that with small, smallers and the smallest signals the low frequencies become weaker and weaker.

yes... as you reduce excitation perm goes down, but adding DC will not take a low perm and increase it in value as you suggest and biasing a core to the maximum permeability level with DC and applying a small AC signal will not give you the same results as exciting the core with that value of AC flux.

to put this in the form of some real measured behavior I took a 11hy 200ma choke designed for choke input duties and measured it with 0.5V @100hz and got 11.6hy with no DC present. I then placed 100ma of unbalanced DC on the core and measured 11.4hy and at 200ma of unbalanced DC I got 11.1hy.

The 1/2 a volt @ 100hz represents an AC flux of 3 gauss and 100ma a Bdc of 3700 gauss and 200ma a Bdc of 7400 gauss. Applying 400Vac @ 100hz gives a Bac of 2500 gauss and increased the inductance to 12.8hy. All of this was on a 0.1mm grain oriented C-core.

dave


 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 18:11:51
megasat16
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 Paul,

I am sure you aware that most Interstages including H series are not rated for DC. Some H series may have DC rated interstage but if DC rating it's not printed in the UTC catalog, it's most likely to be used with parafeed design.

What UTC H series is it? Mine is not made by UTC. I have a few UTC HA series Interstage as well that doesn't measure as linear as the ones in this topics....

Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 18:48:16
hifipaul
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I'm using one of the HA series (I don't remember which one, possibly HA-108). It is being used parafeed to PP grids (1~;1.2+1.2). I've used parafeed before, successfully. The problems I am experiencing, I attribute to the step up design to power grids. Some engineering buddies told me that step ups will be problematic and crap out into grid current, and they were right. Gain is not free.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 19:34:10
megasat16
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 No such thing as free gain. HA-108 is not designed for IT with high Rp tube. Low Source Z of around 600 requires Rp lower than 600 or so for the ideal condition. What driver tube are you using? You mentioned lower source than 900 ohms? But are you already maxed out on the driver plate current for the current driver tube Rp?

Tube IT are supposed to have higher Primary Z not to load the driver tube or the power is wasted on the primary side.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 19:45:41
megasat16
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 Dave,

I am sure you can figure this out on your own. 4mA of current source from 5000ohm resistor driving an equivalent series circuit consisting of DCR, a low value C, and a high value L at 20Hz will result in a distorted waveform.

This will only work if the AC current at 20Hz is much higher like 100mA (smaller value resistor like 1K ohm)or the Signal Generator Voltage is much higher than 21V that mine can put out.

What is the max output voltage on your Signal Generator without distorted sine wave?


Regards,
James


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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 21:45:55
dave slagle
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 Why does distortion keep coming into play here? I am suggesting a simple amplitude sweep and in this case the amplitude will be attenuated long before the signal generator distortion ever becomes an issue.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 28, 2016 at 22:08:29
megasat16
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 Please try and let me know if you see a distortion in your own setup.

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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 05:28:15
euro21
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This is my humble measuring set to test(and measure)chokes and OPTs.

The variable CCS represents constant anode current and generator 1V AC is the AC signal on the tube's anode.

As you can see in the right side it's a simple reactance divider.
Measurable inductor represents R2 (2*pi*f*L) reactance and serial resistor is the -lesser- "lower" resistance of the divider.

The measurements is the simple AC voltage measurement with a little computing.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 05:51:34
dave slagle
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 I am unclear as to why this is suddenly about distortion from my signal generator. I am reasonably confident that if I measure the distortion at the 50 ohm output of my signal generator at 20hz into the primary of an output transformer, and then repeat the measurement with a 5K series resistance the distortion levels at the output of the generator will go down.

If for some reason the goal is to keep a constant input level at the DUT then I see where there could be an issue since as AC current increases, more of the source voltage will be lost across the series resistance requiring an ever increasing output from the generator but the entire goal here is to see a realistic frequency response graph. Attempting to see accurate information of a transformer intending to load a 10 by feeding it from a 50 ohm source doesn't give any meaningful information.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 09:03:20
Lenin



Dave your measurements are way to rough to see any differances.

I mean low frequencies much lower then 100Hz and not only 1 medium large signals as 500mV.

See this picture measure with only ac signal. The low frequency response depends very large on signal level ( i used different probes to get all in 1 picture).
This behave is not present with a SE transformer with dc (at least a lot less).

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 10:00:38
dave slagle
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 There is nothing crude about my measurements.

See this picture measure with only ac signal. The low frequency response depends very large on signal level ( i used different probes to get all in 1 picture).

was the transformer you measured airgapped to handle DC?

This behave is not present with a SE transformer with dc (at least a lot less).

I would expect that to some degree because in order to handle the DC offset an airgap is needed and the introduction of the airgap will temper any variation of permeability with applied signal. A proper test would be to measure the same gapped transformer at various excitation levels with and without DC current and then compare. I predict the transformer with the DC bias will never show more inductance (unless the DC is pulling shut an unstable gap)

TO clarify my statement I am saying it is normal for a gapped SE transformer to show a much smaller range of variation on inductance with applied signal and as signal is increased the inductance will also increase, however this behavior is not a function of applying DC but of the airgap needed to deal with the DC reducing the range of variability. The increase perm seen in all cases is simply due to the increased AC excitiation.

I am also saying that it is impossible for a DC bias on a core to increase the permeability of a core. It can in some cases increase the effective permeability of a core by manipulating the airgap but that is a simple mechanical issue.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 12:54:57
Lenin
 I don't know if your measurements are correct Dave.
I measured today a real output transformer (Audionote Se EI-core) and not a choke but i can't confirm your measurements. At least a factor 2 differance in induction. And because i can't measure with low signel levels wih this transformer i can't confirm my own statements at the moment. Damn!


 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 13:48:33
dave slagle
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 can you please give me the measured results with and without DC current at two different levels of AC excitation.

For example... 1V and 100V at some frequency well below 1Khz (50-120hz) with no DC bias and then repeat the same two AC measurements with like 75% of the rated DC current in addition to the AC.

I have done this 1000 times or more and have yet to find a case where adding DC increases the permeability. The image below is a set of plots of inductance vs. current for a fixed AC excitation. As you can see that the addition of DC doesn't increase the measured inductance and if it did you would see the inductance increase as DC current is added.






dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 13:53:32
Lenin
 ?

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 15:25:35
megasat16
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 Dave,

I know you are here with the intention to help. Therefore, I have tried to to reply in my best possible way and asked you to try it yourself. If I reply in any other way, I would be labeled as insulting.

It's so simple that you only need a Function Generator, a Scope, two 10K resistor, a transformer with around 10K ohm Z.

Set your scope to 21V, 20Hz Sine and put a 5K resistor in series with your SigGen and feed it to your 10K transformer.

I intentionally keep quiet on other topics and cascading transformers for a better reason. Bandwidth of DC to Day Light?

If you refuse to build your own proposed circuit, please let's just keep this topics for the search of suitable tubes.

I have no energy to go back and forth over this simple stuff.

Best Regards,
James

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RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 16:44:03
dave slagle
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 For the plots I attached, the measurement setup is a Genrad 1633 setup sitting 10 feet behind me.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 19:39:03
dave slagle
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 OK...

Set my signal generator to 20hz and a 30V peak-peak signal (maximum output)

measured the FFT of just the waveform into the scope and got this:





I then placed the primary of a 10K:16 output transformer in series with the 50R output impedance and put the scope probe across the 16 ohm load resistor. I then inserted a 5K series resistor with the output of the generator and here are the two FFT's

green is the 50R out and Blue is the 5K50 out.





The loss in amplitude is expected from the finite inductance working against the 5K source but for the most part the distortion remained unchanged.

To keep this complete I also ran frequency sweeps from 1hz to 1Khz with both the 50R and 5K50R source impedance and a 16R load and got the following two sweeps.





again as I stated, the higher source impedance readily shows the results of a finite amount of inductance of this transformer which brings us back to my original point that a sweep of a transformer with a 50 ohm source impedance is pointless unless you intend to use it that way in circuit. Your mention of using a 10 which has roughly a 5K source impedance made me point out that it would be wise to repeat the sweeps with a more appropriate test setup.

I still have no idea what you are referring to about increased distortion and how distortion is even relevant to this discussion but I did what you asked and now it is your turn to repeat the frequency sweeps with a 5K series resistor so we can get a realistic idea of how this device really behaves.

you don't have to take a million data points... Just start at 1Khz and then sweep down to the -1dB, -3dB and -6dB points and that will tell a lot.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 20:14:15
megasat16
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 With the 5K series resistor in place, probe the input Sine Wave and check if it looks anywhere near a sine wave?


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RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 20:27:01
dave slagle
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 It looks exactly like a sine wave. If it didn't the FFT's would certainly show it.

I really wish you could better explain the mechanism that you think will cause all this phantom distortion.

When you do the new frequency sweeps of the LF behavior with the 5K series resistor, I'm sure you can easily document it.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 29, 2016 at 21:01:54
megasat16
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 Why aren't you seeing it? It's beyond me. You don't have to do FFT. And your FFT looks way bumpy to me for a sine wave. I don't know why.

According to your own circuit with 5K resistor limiting to about 4mA-40mA (actual number depends on the actual source impedance of the FG) of current driving into a parallel circuit that has low value DCR of less than 50-100ohms, unknown value C but a large value of L in series with the rate of charge of 20 cycle, you will have a resulting vector of triangular output due to the charge due to the very limited current. That triangular output is now reflected back to the source and combined into a pretty distorted sine wave.

To overcome this, you either need to increases the frequency (charge the C of the primary winding more rapidly) or increase the current to charge the capacitance of the winding at every cycle. It's exactly what I envisioned and exactly what I see. Or the result is incomplete charge cycle resulting in a triangular shape waveform. It's the same principle as ripple in Power Supply circuit.

What's the point of using such distorted waveform since it'll only make everything worse? If you can suggest me to modify your own circuit, I am sure it'll work and I can try.
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RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 05:54:59
dave slagle
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 hey...

Why aren't you seeing it? It's beyond me. You don't have to do FFT. And your FFT looks way bumpy to me for a sine wave.

I don't think I am seeing it because it isn't there. Why cant you post an example rather than a vague description? Plus that FFT ispretty nice for a 20hz sine... the 2nd and third harmonics are approaching -60dB which is in the area of 0.02% distortion.


According to your own circuit with 5K resistor limiting to about 4mA-40mA (actual number depends on the actual source impedance of the FG) of current driving into a parallel circuit that has low value DCR of less than 50-100ohms, unknown value C but a large value of L in series with the rate of charge of 20 cycle, you will have a resulting vector of triangular output due to the charge due to the very limited current. That triangular output is now reflected back to the source and combined into a pretty distorted sine wave.

if this is the case then it should really be easy to see. To make things easier to document I moved to spice to do the circuit and again I couldn't replicate this distortion.

Here are a series of 4 different traces at three different point in the circuit representing a source impedacne of 50 and 5000 ohma and a coil capacitance of 1p, 1n and 1u. If this behavior really exists I would expect ot see at least a hint of it in one of the simulations.





To overcome this, you either need to increases the frequency (charge the C of the primary winding more rapidly) or increase the current to charge the capacitance of the winding at every cycle. It's exactly what I envisioned and exactly what I see.

again please show me some measured or simmed results of this behavior.

Or the result is incomplete charge cycle resulting in a triangular shape waveform. It's the same principle as ripple in Power Supply circuit.

I have yet to see a triangle and pretty thoroughly covered all the things you have said will cause it.

What's the point of using such distorted waveform since it'll only make everything worse?

the waveforrm isn't distorted so no problems with the measured results.

This claim of distortion is yours and I have done everything to try to find it. Rather than sitting there behind a keyboard and insisting it happens why don't you replicate it and post the results? The perfect place to do this would be with the test setup you have already done to measure the transformer in question. Simply measure the output at 1Khz with and without the 5K series resistor and then repeat at 20hz with both. Then a quick pic of the resultant sine for each case should clearly show the problems you insist will happen.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 08:16:23
megasat16
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 Oh Dave, don't you think you are still confusing the series resistor acts only like voltage dividing / current limiting in the source circuit?

I thought about it last night why yours work and mine doesn't. It is both true for the both of us. It's because DCR of the windings and it's just not fixed on all type of transformers, isn't it?

You are using 10K OPT to measure your plot? Obviously, the DCR is high on them resulting a low load (low current flow through the primary 10K winding) on the source circuit thus creating less voltage drop on your source with 5K series resistor. And less voltage drop from the 5K resistor means more voltage appears at 10K ohm input at the primary. Combining bigger voltage with less current drop in the DCR of primary will result in a complete charge of the internal C in the winding.

Thus, it doesn't reflect the distorted waveform I mentioned earlier and the reason you aren't aware of it before.

I will post pics with all that explained earlier. Please standby.

Regards,
James
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RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 08:39:02
dave slagle
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What?

The DCR of the windings really doesn't come into play here since it appears in series with the inductance and the inductance dominates at the frequencies in question.

I really cranked up the numbers and may have found what you are referring to. I increased the winding capacitance to 1u (which is never going to happen) and dropped the frequency to 2hz and got this:





the green trace has 1 ohm DCR for the coils and Blue 1K ohm so it is clear to me that the DCR is not the cause. This was for a single wave cycle at startup and after that first cycle it goes away. Below is the first 6 seconds of a transient response.





dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 08:47:38
megasat16
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 Dave,

DCR is not playing this? Please try your own circuit on the 16R secondary of your OPT to see what I am saying.

You'll find out you have no reason to feeling smart today.

Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 09:38:22
dave slagle
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 I reversed the transformer in the sims and aside from being severely attenuated the sine still looks good.

I'll await your test results showing this.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 09:48:52
megasat16
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You can't sim or model a wrongly assumed SPICE circuit based on the wrong theory and expect to see a correct real world result.

I expect you TRY it with a FG, a scope, real transformers (real stuff)!
The Second pic with the probe before the 5K resistor on the input.

The First pic (top) with the probe after the 5K resistor on the input (or the actual input pins).

Top sine (with yellow color) is the actual output from the FG. The bottom sine (with the blue color) is the measured with the probe.

The probe measurement at the 2nd pic (bottom) is before the series 5K resistor. There is a little small voltage drop due to the internal resistance of the hookup wire.

The probe measurement at the 1st pic is after the 5K resistor which shows the sine wave is severely attenuated to the load from the transformer.

More current flowing through the source circuit thus causing a lot of voltage drop across the 5K resistor. And the small voltage with the limited current supply to the transformer creates a severly distorted waveform.

Here is the FFT (real) curve of the 20Hz Sine! Does it look similar to your FFT? I am not familiar with your FFT plot! I need to study what it is showing.



I will pull the Tango X-10S from the box and measure the Primary and Secondary for you a little later.
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RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 14:12:12
dave slagle
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 I did measure it in the real world with a scope and a signal genrator. the image you post sure looks like core saturation to me.

I'll look at it again tonight.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 16:47:51
megasat16
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 Why hit yourself, Dave?

The saturated core needs one of all of these conditions.

1.) DC on the winding.
2.) Turns Short on the winding. (either primary or secondary)
3.) Crazy Low Load Placed on the Secondary at full power it can handle so the core saturates

When did you see such things happen with the pic I posted?

I will post the sweep from the other transformers I promised a little later.

As I said before, don't make me to go over this simple stuff back and forth. I felt like I already used up a lot of energy trying to make you hear what I have been saying all along.


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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 30, 2016 at 18:38:56
dave slagle
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IF this is the type of waveform you are referring to it is coming from saturation. I was able to get this waveform by simply placing 14,000 gauss of AC flux on an 80% nickel core and this waveform is the result of saturation causing non-sinusodal current draw which shows up as a non-sinusodal voltage when drawn through a series resistance. If you increase the value of series resistance the distortion gets worse.

The saturated core needs one of all of these conditions.

do you mean any of these conditions?

1.) DC on the winding.
I would call that excessive DC on the winding. but yes DC can cause saturation.

2.) Turns Short on the winding. (either primary or secondary)

a shorted turn will cause excessive current draw and distortion du to loss of the load but it will not saturate the core. (see my response to 3)

3.) Crazy Low Load Placed on the Secondary at full power it can handle so the core saturates

This is flat out incorrect. Lenz's Law States that AC current through the secondary does not change the flux in a core (which is why a shorted turn will not saturate) both will cause lots of heating and force the inductance to drop to near zero but they will not cause saturation.

The one big cause of saturation you missed was simple AC excitation. Every time you either double the voltage across a coil or cut the excitation frequency in half you double the flux on the core so as you sweep down in frequency you increase the flux and at some point you are going to saturate that puppy which gives rise to exactly the behavior you are describing.

When did you see such things happen with the pic I posted?

I have seen the particular distortion waveform you posted many times and the cause has always been saturation.

Can you tell me the AC flux on the core you were testing when you obtained that waveform?

 

RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 00:09:29
shane.
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 then find a different transformer..

 

RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 09:08:18
megasat16
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 Your reply is for Me? What kind of transformer (Type, brand, model) do you suggest?
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RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 09:25:05
megasat16
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 It was a long day for me yesterday and I have to do a lot today. But I will try to reply to your post when I can glue my back to the chair today.

Meanwhile, please also take a closer look and tell me these two waveforms are the same?

They both looks distorted sine but the cause of the distortion and the waveform isn't the same, right?








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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 12:28:26
dave slagle
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Sure... they may not look identical so here it is with a little lower source Z and a little less AC excitation.

I still strongly suspect the net cause of the distortion in both cases is nonlinear core behavior combined with a source impedance greater than 0 and the cause of the nonlinear core behavior is saturation.

Can you show this type of behavior with an air-cored transformer or inductor?

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 13:44:23
megasat16
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 It would be useful if you show the whole picture (just like I did) instead of just the waveform so I know where you probe at to get that waveform(whether the input or the output or before or after the resistor).

No, I don't have any aircore inductor or transformer here to take that measurement. Would the Toroid works?

But may be I can wind DIY aircore inductor myself.
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RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 14:05:13
dave slagle
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 Same hookup as you used.

The signal generator has an adjustable output Z so i simply put the 600R output across the the inductor and the scope is also connected across the same two terminals as the signal generator.

If I drop the Zout of the signal generator to 50 ohms the sine looks better. Again this is simply saturation causing distortion of the current waveform which shows up as a distorted voltage waveform when you have any series resistance.

None of this shows up in simulations unless you add a model for the transformer core material into the mix.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 23:19:27
megasat16
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 I think you are close to a self realization. A little closer than before.

Ask yourself these questions. At what AC voltage (ac current) will my core saturation occurred at 20Hz.

I am sure you know that answer. Try in on a transformer if you aren't sure about an inductor. Try the circuit with a series resistor and without a series resistor.

But this time, hook up (preferably a good Fluke) AC Ammeter in series with your source and check the current drawn into the inductor (or transformer) and observe the waveform on the scope.

By your own definition, the core saturation occurred at higher AC current (or voltage) than the core can take?

Compare your AC current drawn for various tests - one without the series resistor that produces clean waveform and one with a series resistor that have the distorted waveform and let me know your measurements.

I probably won't be able to post tomorrow though.
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RE: What tubes to use with this Interstage Transformers?, posted on August 31, 2016 at 23:44:45
shane.
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 My first question would be is the ratio favourable for driving an output stage?. Drive impedance would be at least 16x the Rp of the driver tube, input capacities of the following tube might be reduced by the same amount when reflected back to the driver - but I'm not sure that this is the whole picture.

To answer your original question 'what tubes to use with this transformer?', I think best to find a more suitable transformer for driver plate to output grid.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 00:16:17
megasat16
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 Dear Shane,

This is a Driver Transformer for driving Large Eimac tube so it is correctly designed transformer for driving duty.

With impedance transformation occurred is 1:16, the drive voltage is very large on the Secondary with reduced AC current. But the Grid usually don't need a lot of of AC current unless I want to get into A2 or modulate into C.

I am sure this transformer is good for a few Watts of power handling. So, at 2W, I can use it for 200Vp-p with .01A AC drive into the Grid of the Output tube. I am not looking to make hundreds watt Power Amps. May be something around 8-20W output is great.

The 801A Rl is 10K with 425V B+, 18mA DC current on the plate for 1.6W of driving power. So, this transformer is more than enough to handle that kind of driver tube.
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RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 00:27:44
shane.
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 seems that you have answered your own questions..

(what are you looking for really?)

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 05:14:07
dave slagle
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 I think you are close to a self realization. A little closer than before.

If this self-realization is that a saturating transformer causes a distorted voltage waveform through a finite resistance then that is "old hat" and what I would call a concise explanation of what is happening.

The key point here is if 5000 ohms in series with a signal generator causes these issues, then so will a tube with a 5000 ohm RP.

Ask yourself these questions. At what AC voltage (ac current) will my core saturation occurred at 20Hz.

again.... AC current does not saturate a core. A simple proof of this is to take a 10hy inductor operating at an AC flux of 10,000 gauss and increase the gap size to make it a 1HY inductor. You will now draw 10 times the AC current but the flux on the core will remain unchanged.

I am sure you know that answer. Try in on a transformer if you aren't sure about an inductor. Try the circuit with a series resistor and without a series resistor.

it doesn't matter if it is a transformer or an inductor. saturation is saturation.

But this time, hook up (preferably a good Fluke) AC Ammeter in series with your source and check the current drawn into the inductor (or transformer) and observe the waveform on the scope.

By ac ammeter i suspect you mean current probe for viewing the current waveform on a scope.

Compare your AC current drawn for various tests - one without the series resistor that produces clean waveform and one with a series resistor that have the distorted waveform and let me know your measurements.

I guess the 600 pound gorilla in the corner here is why do we care about the measurements of a device well outside its linear operating range? If the 5K series resistor causes gross visible distortion that simply tells you that it is not suited for audio at that particular voltage / frequency combo.

Earlier on in this thread you said that the Tango NC-20 showed more than a 2dB variation 20-20Khz and if measured from a 50 ohm source I suspect either the measurements are flawed or the transformer is defective since with a 1K source it is flat from 10-100Khz.






dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 07:02:02
megasat16
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 I have nothing against a real 1K source showing the core saturation. It's what I wanted to see and try it for myself too.

I can't, however, take a 1K series resistor, the same as 1K source. It's a limiting resistor and pretty dumb device to call it an AC impedance source.

Check that pic with the Tango curve again for the series resistor; you'll see the AC impedance source is the actual tube and not a series resistor. It's very acceptable to me. This discussion wouldn't never happened if I tried the same circuit with Tango as 1K Rp tube and see a core saturation on the IT I have. It's exactly what I wanted to see.

But whatever reason you think it is, think this yourself. At what voltage the core saturate for a given size transformer. Some small transformer saturate probably at a few volts while others take hundreds of volts to reach core saturation.

If you have a current probe, it's even better. Measure your own circuit with the current probe and post results.
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RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 08:59:54
Tre'
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 "Drive impedance would be at least 16x the Rp of the driver tube,"

Yes.

" input capacities of the following tube might be reduced by the same amount when reflected back to the driver"

The reactance of the capacitance of the output tube would be reduced by 16 times making it harder for the driver tube to drive that reactance.

Bottom line, to use a 1:4 interstage transformer one would need a driver stage with a very low output impedance and a ton of drive current.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 09:08:36
Tre'
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 "With impedance transformation occurred is 1:16, the drive voltage is very large on the Secondary with reduced AC current. But the Grid usually don't need a lot of of AC current unless I want to get into A2 or modulate into C."

The reactance of the Miller capacitance of the output tube will appear 16 times smaller to the driver tube and it will take current from the driver tube to drive that.

16 times as much current vs. a 1:1 IT.


Tre'



Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 20:58:28
megasat16
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 Tre,

I agree the Cmiller is something to watch out for in all Triode circuits. It effects the Frequency roll off and the the previous driver stage driver capabilities.

But I think you meant the current in the primary needs to be able to supply 4 the load current of the Secondary.

So theoretically speaking, 20mA at 100Vrms (2W) driving power requires a little more than 25Vrms of 80mA of the power applied to the IT primary. So in the case of 801A, 70Vp-p (or 100Vp-p) with 80mA of current should be about 1.6W of power. But it doesn't sound very right, right?

So, I am looking at a little more than 150Vp-p with 40mA of driving AC current for about 600Vp-p with 10mA Grid current into the Output tube? I think this sound much realistic. 150Vp-p through 1:4 will be enough to compensate for the Cmiller from the Output tube.


Regards,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 21:00:42
megasat16
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 I think you need to read Post #1 or the very beginning of this thread. I am looking for the suitable Triode (DHT) output tubes and the driver tubes to be used with 1:4 IT.

I have some answer but I don't have all the answer. And I am seeking more answers from the people who has walked down this path before me.

Is that clear enough for what I am looking for?
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RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 21:30:39
shane.
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 ..mate I dont need to do anything.

good luck with your endevour.


 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 21:50:08
megasat16
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 Yep. You don't need to do anything and I wasn't asking anything from you too. I only answered because of your questions or the lack of reading comprehension and don't know what I am looking for.

But obviously, you enjoy one liner every now and then.

So, Good Luck to you too for more chances to post one liners every now and then.


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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:06:35
shane.
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 Cute. Retarded, but cute = and aren't they all.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:15:53
megasat16
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 Mirror Mirror on the wall, look who's talking now?

I will take it. Better than a retarded Moron every time of the day!

Enjoy one liners while you can...Life is short.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:17:57
shane.
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 wow. so far gone. seek help.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:20:21
megasat16
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 Seeking help is exactly what I am doing here. I still didn't ask you do anything including reading my posts. Enjoy mate!

I usually have a couple of trolls for Supper before midnight.
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RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:30:06
shane.
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 One line.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 1, 2016 at 22:39:24
megasat16
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 Agreed!
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RE: What tubes to use with this Interstage Transformers?, posted on September 2, 2016 at 19:25:28
Tre'
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 Well, we can look at this from either side.

Let's see what the grid of the output tube sees looking back through the IT to the driver stage.

The 5k output impedance of your driver tube will look like 80k to the grid of the output tube.

AFAIK, 80k will not properly drive the Miller of any DHT I am aware of.

If you had a driver stage with 500 ohms output impedance that would look like 8k ohms to the output tube and that would be fine in most instances.

Tre'




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"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 2, 2016 at 23:30:32
megasat16
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 Hi Tre,

Thanks for making me see the coins on the flip side.

So, I do some more reading on the Cmiller effecting the total Cin of the Triode.

I know you gave me an example before and the this pretty much seems the same except this paper has no mentioning the Grid Current Requirement.

http://www.aikenamps.com/index.php/what-is-miller-capacitance

Since I don't have any Output tube in mind, I can't do an actual Cin calculation for this discussion yet. So, let's presume the Cin is 1uF of an unknown DHT which is a unrealistically pretty big for a tube.

So, in the Triode, the 1uF appears at the Grid of the Tube and termed Cin, yeah?

Let's say the 600V AC (from my last example yesterday) appears from the Grid Pin of the IT and present to the 1uF Cin of the Tube.

At this point, what happened to that voltage at the Grid? Will it not go inside the Grid of the tube? Will the Grid of output tube draw a lot of current from the IT so the voltage becomes very small?

Since the Grid is loaded on 1:4IT, will it load the driver tube from the ideal Rl? Ideally, the Rl is higher than Rp of the driver tube not to excessively load the driver tube during Grid Current demand.

But here is what I am thinking. If a 1uF Coupling cap is put in between the Plate of the Driver Tube and the Grid of the Output tube, does it present the same condition as Cin to the Driver tube? Even a very small amount of AC seems to pass through the coupling Cap fine. Then, why it won't it pass through another 1uF Cin inside a glass tube? It'll just be two 1uF caps in series in the circuit.

Thanks,
James
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 3, 2016 at 14:33:06
Tre'
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 Miller capacitance is not series capacitance, it's shunt capacitance.



Tre'
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RE: What tubes to use with this Interstage Transformers?, posted on September 3, 2016 at 21:06:47
megasat16
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 There is some current through 1:4IT but how much is required?

A simple 1st Order RC filter will filter at 6dB/octave or the 20dB/decade beyond Fc. It doesn't matter how much current you are supplying at Fc because Voltage will just be attenuated due to the Xc. The only thing to reverse is to supply a bigger Vin to negate the roll off or uses a local feedback to reduce the gain (thus changing Ctotal value to shift the Fc).

The drop is 3dB at Fc. So, ideally we want to see Fc at 20KHz or beyond. If Fc is at 20KHz, the FR roll off probably starts at around 18KHz.

The nice thing about the 1:4IT I have is that it'll slightly adds about 0.5dB gain from 14KHz and beyond so it'll somewhat negate the effect of the Triode roll off.

As to the Grid Current Requirement from the driver stage, it would be impossible for the circuit below to work.

But it was published in the MJ magazine so it must work. I really like to see how it measures and where the Triode Roll off begins.





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RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 01:20:27
Lenin
 Published in MJ dosn't mean it works good.....


Look at the inputstage stu-001. 100k output and driving a 211, also a 100Ohm potentiometer infront of the stu 001. Terrible

And also 2 output transformers in serie, wow! Even more terrible.

These circuits are for MyFi projects, with weird high colored speakers systems. Not the usual Hifi home stereo.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 08:23:25
Tre'
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 "A simple 1st Order RC filter will filter at 6dB/octave or the 20dB/decade beyond Fc. It doesn't matter how much current you are supplying at Fc because Voltage will just be attenuated due to the Xc. The ONLY THING to reverse is to supply a bigger Vin to negate the roll off or uses a local feedback to reduce the gain (thus changing Ctotal value to shift the Fc)."

That is not true. A lower drive impedance means the Fc is shifted higher, out of your way. That fixes the problem at it's core.


"The drop is 3dB at Fc. So, ideally we want to see Fc at 20KHz or beyond. If Fc is at 20KHz, the FR roll off probably starts at around 18KHz. "

One octave below the Fc is the -1db point. So a Fc of 20kHz means you are still -1db at 10kHz.


The phase is disturbed for a decade.

So, ideally we want to see Fc at 200KHz or beyond.

That is why, for a low pass filter, if you want 20kHz undisturbed you need the -3db point to be 200kHz.

And at the other end, for a high pass filter, if you want 20Hz undisturbed you want the -3db point to be 2Hz.

All of that aside, you should look closer into Miller capacitance and what it takes, current wise, to drive shunt capacitance.

Tre'
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"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 11:01:07
megasat16
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 I am a little rusty on the filters and I stand corrected on the roll off points.

However, I want to standby my own account of increasing Vin proportionately to the attenuating Slope passing Fc point to remain the constant Vout from a low pass RC filter circuit. Since R is fixed value, it can only supply a maximum current to the shunt C when Xc is effectively becoming a short at very high frequency. R is always been fixed and Vin is fixed so how much maximum current (Imax) it can supply through the R is fixed too. The only thing changes is that the load current demand which is based on the Xc. It's just that Xc comes into play based on how much current it gets from series R and how often it gets charged.

Even though Xc is the reactance components, it still is really a cap and the charge across the cap at various frequency.

Before the Fc point, the Xc is high so it does not present a very current demanding load to the R. Voltage drop across R is small or none due to the Xc being high.

Passing the Fc point, the Xc value gets smaller and smaller thus shunting more current to the Ground. This creates a bigger voltage drop across the R and smaller voltage appears at the C.

But When the series R reaches the max current it can supply due to the Fixed Vin divided by it's own value, the Imax is reached regardless of how lower Xc goes.

To overcome this attenuation, you need a larger Vin passing Xc point since the R is fixed to supply more current. You can't get more current through a Fixed value R and a fixed value Vin / Vsource regardless of how much current is made availalbe at the Vin / Vsource or anything in front of the R. The R value itself it the limiting factor here when Xc is effectively becoming a short circuit to Ground.

So, let's get back into the RC filters and shunt cap drive requirement.

In RC series filter, R is usually fixed. And the C is fixed as well since it's inside the tube.

To get more current into the C, you can either increase the voltage (resulting more current flowing through the R) or lower the value of R (as your suggestion).

Lowering R sounds good if it's possible since it's the simplest and easiest. But this defeats the whole point of this thread which is to find the usable tubes with the 1:4IT.

Or we can reduce the C value for a fixed R value? Since the R is fixed in my case, we can find the tubes with low gain since the open loop Gain has the most effect on the total C. It's exactly what I am hoping to find.
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RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 11:29:04
megasat16
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 I agree to your on the cover assessment of how that circuit works or sounds.

But the MJ magazine is not a small Internet Magazine. It's not known to most people outside of Japan but very highly respected in Japan. If it's comparable, the Japanese audiophiles holds MJ in the same regard as that some of us do for the Stereophile magazine in the U.S.

http://www.preservationsound.com/?p=1286

Anyway, the circuit you've seen was done by Sakuma. He has possibly made tens or even hundreds of these eyebrow raising circuits. I can only wonder how they sound but he is well known inside Japan for his nontraditional circuits and the self made DHT amps.

I don't think Mr. Susumu Sakuma holds an Engineering Degree but he is no small fry in the DHT circuits.

http://www10.big.or.jp/%7Edh/

I wonder how it really sounds though. May be No Highs, No Lows, just the perfect midband? I don't know but Bose has a pretty good fan base too.

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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 11:35:43
Tre'
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 Where is "R"?

Tre'
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RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 11:55:43
megasat16
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 R is the fixed R between the plate of the Driver and the Grid of the Output tube in the Direct Coupling Circuit.

Or if it's eliminated, it's the Rp of the Driver / Source.

And you are saying 160Kohm impedance of the IT as the R in this case.

I don't think Z(IT) is in series with the Shunt C at all in the IT circuits. It is effectively Rp.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 12:32:10
Tre'
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 "And you are saying 160Kohm impedance of the IT as the R in this case."

I am not saying that. I never said that.

"I don't think Z(IT) is in series with the Shunt C at all in the IT circuits. It is effectively Rp."

Correct, if the IT is 1:1 then Rp (not really Rp but the output impedance of the driver stage) is reflected to the secondary and that is the source impedance and the "R" used to calculate the effect of the Miller Capacitance.

But with a 1:4 winding ratio IT we have a 1:16 impedance ratio IT so "R" is the output impedance of the driver stage times 16. That's is what I have been saying.


BTW Transformers do not have impedances. They only have winding ratios.

Transformers are made to work with certain impedances. The inductance and winding capacitance dictate that and that is what the "impedance rating" of a transformer is all about.

But that is not to say that they have impedances of their own. They don't.

Transformers only "reflect" impedance according to their impedance ratio.

The "R" presented to the primary will reflect to the secondary and the "R" presented to the secondary will reflect to the primary.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 12:32:40
megasat16
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 And with this, we are now back at Square 1.

Reducing Rp will have more current available to the C. I don't think I disagree with that. It just meant a different driver tube other than 5K Rp in the case of 801A.

But really, how much current a Grid needs? Elimate the IT and the fixed resistor R in the direct coupling circuit and substitute with the short so the Vsource is the same as the low Rp tube like 500ohms. Fc will shift due to the lower Rp (or R in the RC) value but passing that Fc point, the attenuation will occur the same. Rp values are fixed too. In a way, it is more current avilable till Imax is reached. But beyond Xc point, it'll all be just the same all over. Fc is shifted due to the R being smaller.

So, you can't make more current available without changing Rp (the tube itself) or the IT. I think it's all you have been saying that 1:4IT won't supply enough current due to it's high Z value and the Fc point will occur within AF band.

I also think I have been saying that Triode Roll Off will happen. But when you say it won't work, I started misunderstanding why won't it work.

But I think we are all saying the same thing in a different way.

Essentially, your choice is not to use the 1:4IT which I understand and respect that.

But my choice is to use the IT I have and to work around it and find a suitable tubes for it. I think you have mentioned that it would be very difficult if not next to impossible?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 12:38:39
Tre'
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 "Fc is shifted due to the R being smaller."

Correct but with a low enough Rp (and it not being multiplied by a step up IT) Fc is high enough so it no longer matters.

"Essentially, your choice is not to use the 1:4IT which I understand and respect that.

But my choice is to use the IT I have and to work around it and find a suitable tubes for it. I think you have mentioned that it would be very difficult if not next to impossible? "

Yes, and I will say it again.

If you had a driver stage with (let's say) a 500 ohm output impedance, that 500 ohms would look like 8k ohms to the output tube's grid and Miller C. As long as the output does not have too much Miller C then the 8k ohms would drive it just fine. That is to say the Fc would be high enough as to not matter.


Tre'

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"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 12:59:49
megasat16
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 Yes! I agree to that.

That's truly make it difficult to design a circuit for Fc out of 200KHz not to be effected by the RC filter slope.

So, let's say your Fc moves out to the 40KHz instead of 20KHz, the low pass attenuation starts at around 4KHz?

Now, here is the advantage of the 1:4 IT I have. It slightly adds more Voltage gain at the rising frequency so it'll negate that effect of the Low Pass filter loss and puts an overall FR of the final output a little flatter. You normally don't have that advantage with a constant voltage sources.

Now back to the transformer impedance, it was specified by the manufacturer at a certain (unknown to me) frequency as the starting point. But it is the Audio IT, I can safely assume that is the the optimum load it present to the Source during the AF Band.

Since I can't measure and don't know the exact value of it, I must use it as an optimal loading point to the Driver Tube and find an appropriate driver tube. Lower Rp driver tube does not pose a problem but Higher Rp driver more than 10K Rp will be loaded by the Transformer Primary.

It's the same reason you can't put 600Ohm Primary IT on the 5K Rp tube since it'll just load the Voltage in the primary and drop most of it on the primary side and less current (or AC Flux) is available to the core and to the secondary side. It's the opposite of Saturation (current starving core) which looks like a saturated core. I think Dave and I had quite a lengthy discussion of that.

Anyway, I appreciate you taking seriously to make me see through this.

Sometimes, things got lost in translation and my apologies for that. But I think we are essentially on the same page with a different approach to the solution.




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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 17:43:44
dave slagle
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 For the sake of showing actual low frequency information, a 50 ohms source with a 1K series resistor is no different than a tube with an Rp of 1050 ohms.

A fair bit of good info has been offered up for you to digest here and I have a strong suspicion that there is no way this transformer has any chance whatsoever of loading a 10 / 801 and getting anywhere near flat from 20-20Khz into the grid of any triode. Simply placing a 5K resistor in series with the input signal and 100pf of capacitance across the secondary will quickly tell you if you have any chance of being flat from 20-20Khz with a tube like the 10.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 18:45:10
megasat16
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 So, you are saying whatever resistor connected to the source becomes the actual source including the resistor value?

50ohms impedance with 1K series is 1050ohms source and 5K becomes 5050ohms source?

So, why don't we just all use 5K ohm OPT in series with a 5K ohm resistor and call it a true 10K ohm transformer? After all, it's much easier to make better performing transformer with lower Primary Z, right?

Your assumption of adding R is part of the FG is only correct if that R is placed inside the Function Generator and performs part of the circuit or the transfer function in union with the capacitive reactance Xc and inductive reactance Xl of that circuit.

But placing a series resistor R outside the function generator is really a current limiting for the FG and causing voltage drop across it as the load varies (with or without varying frequency). It's really that energy is lost in that resistor and not transferred to the Transformer. It must be why no one wants to use 5K Zp OPT with another big dump 5K resistor to waste energy (power). It also limits the current flowing through the 5K series primary.

It gets much simpler when you define a voltage source and a current source and an AC impedance source.

What can AC impedance source supply to a short circuit? Voltage drop across it's own internal resistance or impedance value and current proportionately to that resistance or impedance value right?

What can AC impedance source with 5K series resistor as in your suggest supply to a short circuit? Find that out for me and let me know. Where does the voltage drop occur at with respect to Ground?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 18:50:38
megasat16
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 Other than me disagreeing with your theory of using 5K series resistor, I am just as interested to see how it performs with an actual 5K or 10K source.

Any other method do you have in mind other than building an actual circuit in a short time? I can prototype a circuit but time is not favorable for me right now.




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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 19:08:04
megasat16
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 I think the problem lies with the question of what part of the circuit the resistor belongs to when it is placed after the FG (source) but in series with a Load (Transformer).

Dave is seeing that series resistor as part of the source.

I always see that resistor as part of the load circuit and the actual source is the FG.

Can someone simplify it for us once and for all?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 19:54:36
dave slagle
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 So, you are saying whatever resistor connected to the source becomes the actual source including the resistor value?

yes.

50ohms impedance with 1K series is 1050ohms source and 5K becomes 5050ohms source?

yup.

So, why don't we just all use 5K ohm OPT in series with a 5K ohm resistor and call it a true 10K ohm transformer?

It will provide a 10K load to the source but the problem is 1/2 the voltage will show up across the resistor and 1/2 across the transformer primary netting only 1/2 the voltage being delivered to the load.

Your assumption of adding R is part of the FG is only correct if that R is placed inside the Function Generator and performs part of the circuit or the transfer function in union with the capacitive reactance Xc and inductive reactance Xl of that circuit.

really? pit the resistor in the box and it suddenly disappears? My signal genrator has a variable output impedacne (50, 75, 135 and 600r) and it is accomplised by a switched resistor network at the output of the device. Sure those resistors are in the box but behave no differently that a similar resistor outside the box.

But placing a series resistor R outside the function generator is really a current limiting for the FG and causing voltage drop across it as the load varies (with or without varying frequency).

that is pretty much the definition of output impedance.

It's really that energy is lost in that resistor and not transferred to the Transformer.

again that is what output impedance does.

It must be why no one wants to use 5K Zp OPT with another big dump 5K resistor to waste energy (power). It also limits the current flowing through the 5K series primary.

If you drive a 5K source from a 5K load you lose 6dB of voltage.

It gets much simpler when you define a voltage source and a current source and an AC impedance source.

then you just need to understand how to implement what you define.

What can AC impedance source supply to a short circuit? Voltage drop across it's own internal resistance or impedance value and current proportionately to that resistance or impedance value right?

right so i you add series resistance to increase the source impedance ohms law dictates that you must also limit current. "current limiting" is not a function of added series resistance it is the result of it.

What can AC impedance source with 5K series resistor as in your suggest supply to a short circuit? Find that out for me and let me know. Where does the voltage drop occur at with respect to Ground?

it can source the exact same thing as if it had a 5K output impedance and no series resistor.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 20:06:14
dave slagle
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 If you look at a circuit from two different points you will get two different answers.

from the perspective of the source (ie 50r output of the signal generator) the 5K series resistor becomes part of the load.

from the perspective of the transformer primary, the 5K resistor becomes part of the source impedance.

when you want to analyze a source / load combo you need to take a single point in the circuit and then look at all of the paths to ground. In this case the only thing of interest is the primary of the transformer so looking backwards the source impedance driving it becomes the parallel combo of every path to ground. Take a signal generator with a 50 ohm output and parallel it with a 1 ohm resistor to ground and your source impedance is now just under an ohm.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 21:15:04
megasat16
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 No matter from where I look at (i.e. From the input pin of the transformer or from the output pin of the FG, I only get the same answer). That resistor is in series with the input pin of the transformer. Thus, creating a current limiter and (variable) voltage drop across it depending on the load impedance of the transformer based on the different frequency.

That's the way I see it no matter where I look at.

Now, what is that wonderful Engineering marvel FG of yours? I would like to look it up and see what kind of circuit it is constructed with.

Have you ever opened it up and see the impedance selector switch selects different resistors or resistance values? And are they the series resistor inside the FG box with the value of 550, 250 and a short wire?

I wonder why no Engineers from HP, and Tektronix never send a box of resistors along with the FG for the end user to transform the source impedance like you mentioned. It would be very useful for sure.





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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 4, 2016 at 21:22:58
megasat16
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 Putting a resistor or resistor selection switch inside the box does not make it disappear. It makes it part of the circuit inside the FG and reacts along with other components inside that circuit.


Putting a series resistor outside the FG puts a series or parallel resistance to the load and I always look it as part of the load.

I don't know what is used inside the FG for switching impedance values but let's say it used series or parallel resistor of different values.

Let's say it uses 550ohm resistor for 600ohm impedance, do you can think you can substitute a 550ohm resistor inside that FG with 9950ohm resistor to make your FG look like 10K source impedance?

I would love to have something like that.



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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 08:09:34
Tre'
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 "No matter from where I look at (i.e. From the input pin of the transformer or from the output pin of the FG, I only get the same answer). That resistor is in series with the input pin of the transformer. Thus, creating a current limiter and (variable) voltage drop across it depending on the load impedance of the transformer based on the different frequency."

That's right but what you are not understanding is that the output impedance of a stage is always in series with the "input pin of the transformer".

What this means is, if you have,

1. a source circuit with an output impedance of 5050 ohms

or

2. a source circuit with a output impedance of 50 ohms with a 5000 ohm series resistor added

They will both have a total output impedance of 5050 ohms and will behave the same.

Tre'


Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 08:18:53
dave slagle
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 I think you just need to come up with a fundamental understanding of what source impedance is because you keep defining it over and over and then say it cant be.

that pesky variable voltage drop is exactly what you are looking for and is caused by a finite inductance working against a known source impedance. If we drove everything from perfect voltage source then we would get bass response down to DC.

The signal generator is a wavetek 288 and there are switched resistors right at the unbalanced output. I asked a guy at audio precision how they define their source impedance and he also said they switch a "resistor" at the output. I'm sure the guys at HP and tek are also smart enough to put those resistors (or an equivalent sand device) inside the box.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 08:28:58
Lenin
 Adding a 5k resistor to 5k transformer dosnt make it a 10k transformer because the winding ratio is still the same. You just add extra loss to it.



 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 08:29:39
dave slagle
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Joined: April 27, 2001
 Putting a series resistor outside the FG puts a series or parallel resistance to the load and I always look it as part of the load.

it is part of the load to whatever is driving it. (whatever is upstream) and it becomes part of the source impedance for whatever is downstream.

Let's say it uses 550ohm resistor for 600ohm impedance, do you can think you can substitute a 550ohm resistor inside that FG with 9950ohm resistor to make your FG look like 10K source impedance?

yes... that is how it works.

I would love to have something like that.

this whole discussion has stemmed form your refusal to accept this simple fact so you can either accept that you already can do it or deny it and continue to redefine electrical theory.

dave

 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 12:22:26
megasat16
Audiophile

Posts: 207
Location: SoCal
Joined: April 15, 2015
 Firstly, there are a lot of Dave Slagle on the world so I wanted to make sure you are whom I think you are.

Are you from Intact Audio who makes Transformers?

Secondly, I don't redefine anything. I followed what I learned in school many decades ago and do either AC Analysis or DC Analysis completely (not both together as I see fit).

If there is anyone redefining it, it is you who insists upon it as the convenience of simplifying circuits to your theory and advantages instead of the analysis and theory that is taught and learned by millions of E.E or E.T around the world.

Thirdly (or) lastly, I now understand where your misunderstanding and confusion arises from.

I attached a couple of pics taken straight from the schematic of your WaveTek 288 user manual downloaded from the BAMA site.

Please tell me exactly how these attenuators are used in the circuit?

Are these series resistors part of the circuit or not part of the circuit (outside of the circuit even though they are put inside the box) in your WaveTek?

Regards,
James











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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: What tubes to use with this Interstage Transformers?, posted on September 5, 2016 at 12:27:44
megasat16
Audiophile

Posts: 207
Location: SoCal
Joined: April 15, 2015
 Tre,

What you said is only true if you connect your source to the purely resistive load. You can't even start to think they are a real AC impedance source has an open ended series resistor connected to it.

And how is the load connected to the source (series or parallel)?

Regards,
James


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.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

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