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In Reply to: RE: Resistor on the interstage transformer posted by howardyu on August 20, 2015 at 19:59:12
Resistor is there to keep the HF stable.
Better to not use one IF the interstage
is either good enough or properly chosen.
A 1.5K tube into a 10K interstage is bad
and leads to HF resonance so the resistor.
A 5K tube into a 5K interstage is bad
and leads to loss of frequency response.
Now a 2K tube into a 5K interstage is good.
No need of a resistor IF the interstage is good.
DanL
Follow Ups:
What about a bifilar 1:1 IT ? I found with a dirt-cheap £30 Hammond 126B and also C models , adding a resistor worsened the measured response and also the sound . So I ran these devices wide open . Lundahls on the other hand , I had a different experience WRT the secondary resistor but these were for pushpull rather than SE useage
From my experience with the 126 , a lower driving Ra is preferred...
The impedence specifications I always find misleading with IT's . What manufacturers should always specify is the ratio and primary inductance along with ungapped DC current rather than this generalised 'impedence' thing .
Al
Best is to measure the transformer. Most manufactures don't give datasheet so its a bit gambling...Bifilair 1:1 are mostly excelent transformers but, you have to use very good wires for good isolation. Standard transformer wires are not the best wires.
If a transformer has some resonance problems a resistor could help but for a 1:1 i would say the transformers sucks .
Edits: 08/24/15
The insulation rating is one thing Hammond fails to quote on the specs . I have , so far only used tubes such as 6S45 , EC8010 , 4P1L and type 46 , with these IT's . I wouldn't want to risk an 845 with -120V bias one end and driver HT of 400V on the other .
Al
You could do a little experiment with the wires.
If you can solder them (at temperture 450 degrees Celcius) the wire is probebly a normal transformer wire single coated. I wouldn't try to high voltage differance on those wires.
A 1:1 Interstage transformer is only 10k if the secondaire load is also 10k , or 5k if the secondairy load is 5k.
You can use any tube to drive it but the frequency response depends on the tube. Low Rp have better frequency respons then a tube with high Rp.If the interstage is not good designed there could be high frequenty oscillations, specially with tube with a low Rp. Look at a squarewave of 10kHz or 20kHz, it should be without ringing or overshoot.
Better designes have also lower copperloss and better core materials.
Edits: 08/23/15
Incorrect Sir
Interstages are designed to function
with a certain band of Rp tubes.
Outside of that band and you get
poor frequency response (Rp too high)
OR
high frequency ringing (Rp too low).
Like anything else, interstages are
a balancing act with many parameters.
It is these parameters that define
the interstage's rated load -
not the secondary load.
That can also be said of an OPT too.
Change the secondary load and
therefore change the primary load BUT
any transformer will tell you that
you will have a poorer performance
when you do that.
This is because of the many parameters
that are juggled to get best performance.
DanL
What was the last time you designed a interstage1:1?
The reflected load is equal to the loadresistor because N=1. Output impedance is equal to Rp for the same reason.For good low frequency response the inductance has to be high enough for the tube you use, so for high Rp tubes you need more inductance then for low Rp tubes for the same frequency response.
If propper designed there is no ringing or overshoot, whatever tube- interstage combination.
The picture shows an interstage loaded with 220k secondair and 5k. Source 1k Ohm, 60mA dc.
Changing the source just change the frequency bandwith, no ringing!
Edits: 08/23/15 08/23/15 08/23/15 08/23/15
You forget about ...
Parasitic Capacitance
Leakage Inductance
Core Loss
Wire Loss
Thermal Deviation
Transfer Efficiency
There are many more factors but
those are off the top of my head.
It is not as simple as you think.
DanL
Hey, would the moderator who keeps deleting my post kindly go fuck themselves?
I know it helps your eccentric image to let these nuts run rampant, but some of us are here for technical discussion.
Infamous sockpuppet
Garg0yle,If your posts would be more ontopic there would be no reason to remove them i guess.
You can also start a new topic if you like.
Edits: 08/23/15
I got no post on this thread from you?
Maybe it never posted?
DanL
I didn't forget all these things you say but maybe other manufactures did....
The example transformer you see above has very high frequency response so don't worry about those capacities and leakages. Copper resitance is low, about 50 Ohm primair and 50 Ohm secondairy. For lower core loss i used an amouphous c-core.
An 1:1 interstage is very easy to make, output transformers are different.
But anyone will tell you the test of a good interstage
is when there is no resistive load on the secondary.
IMO They sound much better that way too.
Without the resistive load,
how is the HF response?
That is when you need the proper tube
for the interstage.
THAT is what the 2K, 5K or 10K spec
is there for.
For the proper tube for the interstage
or vice versa.
DanL
For me the sound is also better if unloaded. If you have a good interstage there will be no overshoot or ringing.
I did make a lot of interstagesand i have no such problems.
Yes, the sound is definitely more open without padding resistors. There is also more magic when the IT can handle the driver tube's DC in the primary...
For splitting phase in push-pull applications, gain and impedance matching while sometimes lessening the number of needed gain stages, ITs are hard to beat. As the finest push-pull phase inverter, my namesake has indeed brought me closer to the real music...
So, sv572-10, you have built many excellent ITs ? Could you build me some 1:1s to match 245s to PP 245s that can handle 40 mA in the primary ? How about matching a 210 to 210s in PP with a bit less DC in the primary ? I could trade you tubes or $$...Best Regards....
I sended you a pm.
DanL, Thank you very much !
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