Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Return to Tube DIY Asylum


Message Sort: Post Order or Asylum Reverse Threaded

Is this regulated filament supply any good?

62.163.171.12

Posted on October 25, 2014 at 01:28:16
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005





Hi,

At one time I decided to build a Velleman Kit (K7203) to use a a regulated filament supply, also giving me the possibility to adjust the filament voltage easily over a wide range (to use different tubes).

I use 4, one each for the VT25 drivers and 300B finals.

It works splendidly, but I want to hear your opinion of this implementation vs a Coleman Regulator. Although noise performance is super and it all sounds great, I'm not sure this implementation addresses the following problem as addressed by Ron:


"The 5,0V filament carries filament dc voltage but also the anode-current Ia. At the 2 ends of the filament there is a 5V difference caused by the heating voltage - and this makes a current-flow across the filament of MUSIC-signal! This is because the gm of the triode is different at the +5V end compared to the 0V end.

This is normal, it is natural.

But when you connect a voltage regulator, the feedback action of the LT1084 will try to CORRECT the Music signal flowing in the filament. The regulator thinks the music-signal is an error! so you get a bad situation where the LT1084 is trying to compensate for the Music. This is the reason why the voltage-regulator desreves its BAD reputation for making bad sound.
"


Is this feedback/correction problem present in the regulator I use?

Thanks,
NC

 

Hide full thread outline!
    ...
RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 05:45:11
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
With all sincerity I don't believe ANY of the mentioned regulator solutions (voltage regulation by means of LM317 or similar) actually has that feedback/correction problem.

If the regulator could act against the musical signal, it would cancel it, if not 100%, than to a very high degree (let's say 60dB cancellation). This would be obvious as a much attenuated power output and audible even to those with poor hearing abilities. As an illustration, take the LM317 CCS example and remove the bypass cap: the output will be almost totally attenuated i.e. cancelled by the action of the regulator (setting a constant current).

The problem with voltage regulators is the same as for all other DC heaters solutions: the fact that the filamentary cathode is not on the same potential throughout, and there is a difference in operation from one end of the cathode to the other. This is the reason why AC sounds better, the cathode being at the same potential.

AC of course has one major issue, hum. Another issue related to AC is intermodulation. One has to weigh the two alternatives and decide on the compromise he is willing to make.

High frequency AC generated by means of modified electronic transformers (half-wave bridge) is most probably the best in terms of sound (AC, thus cathode at the same potential) as well as noise/hum (even if 30kHz, the 2nd harmonic, much attenuated, is 60KHz, which cannot be effectively reproduced through output transformers, nor reproduced without enormous attenuation by the tweeters, let alone heard by humans). The frequency is too high for audible heterodyne effects, although some claim irregularities may be observed on a scope using sine wave signals: but music is not a sine wave, rather a series of impulses differing in frequency and magnitude as well ss decay and duration...

The main issue with HF AC is effective measurements and the relatively difficult calculation/adaptation. But once one surmounts the initial difficulties it is both great sounding and reliable.

Now the usual inquisition can do it's best trashing me and my suggestions/design work/achievements - while I am going to exercise a new skill: ignoring bashers and haters ;)


******

http://rh-amps.blogspot.com/

 

RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 05:51:33
Chipregs tend to be quiet but don't sound good . I would recommend a ring of two CCS , Coleman reg or if you have the space LCL . Whatever you use , a choke input supply with schottky rectifiers is a must .

Al

 

RE:maybe mod these Ask TK, posted on October 25, 2014 at 06:03:47
amnesiac
Audiophile

Posts: 717
Joined: August 21, 2002
As it happened I was just buying another pair of these when I saw this. I stopped off to drop in some eimac links I found.

This is triode kingdoms idea. This is my next attempt at heating big eimacs. Maybe it worth considering for smaller filaments too.

 

RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 07:49:00
Tre'
Industry Professional

Posts: 17260
Location: So. Cal.
Joined: February 9, 2002
"This is the reason why AC sounds better, the cathode being at the same potential."

That statement confuses me.

5 volts AC would swing the cathode from +7.05 volts peak to -7.05 volts trough.

That's a difference of over 14 volts, end to end of the cathode (filament).

Am I missing something?

Tre'


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

 

RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 09:55:48
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
Yes, you are missing the difference between static and dynamic.

Statically, a tube in class A always draws the same current, for instance 50mA. But in dynamic terms, it actually swings between, for instance, 20mA and 80mA. Meanwhile, the static anode voltage of, for instance, 300V swings from 380V to 220V (idealized values to give an example).

If a CCS is applied forcing 50mA of current draw, it will prevent the tube from drawing more or less current, and amplifying the input signal, unless there is a separete bypass path for AC - a bypass cap. Now that is the difference between static and dynamic regimen.

In similar fashion, the tube is heated with 5V and the bias for the mentioned operating point is -40V. This equates to 40V of potential difference between cathode and grid (cathode being 40V more positive than the grid). Assuming automatic bias, the cathode should be at +40V in static terms, obviously. This is true of an indirectly heated tube, regardless of heater voltage supply type. Now in a directly heated tube, the heater is the cathode, thus if we apply 5V AC to power the heaters - each end (the whole length of the heater-cathode) will be at +40V potential (DC, obviously). With 5V DC across the heater, the midpoint is going to be at +40V while one end will be at +37.5V and the other at +42.5V (DC).

This means that one end has 37.5V potential while the other has 42.5V, which implies a difference in current draw (static) from end to end, and consequently a difference in emission between the two ends - one is obviously more heavily biased than the other.

As explained, with AC used to power the heaters, the whole cathode is at the same DC potential. Both ends are identically biased and have the same emission. The tube operates more uniformly than with DC powering the heaters.

I hope this explains it. Everyone who has got an amp with DH tubes can measure and verify this for himself, although I guess the math is clear enough even without measuring anything.
******

http://rh-amps.blogspot.com/

 

RE:maybe mod these Ask TK, posted on October 25, 2014 at 10:11:06
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
Indeed I was told when presenting my first attempts that other people have already done that approximately a decade ago. At the time those electronic transformers were more crude and operated at lower frequency, thus altering the frequency was considered necessary.

Nowadays even cheap units operate at 30kHz while the better units operate at 50-60KHz. Even the cheap ones have proved themselves as being inaudible in operation, and if adequately sized can be extremely reliable, plus the resulting voltage is much better regulated than the product of normal transformers (much less output voltage difference in respect to AC mains difference).

I have applied those to 813s which consume 10V 5A, with fantastic results, while having a low consumption for the heaters circuit and achieving a very small sized power source for them.

The sound is cleaner and more refined even than standard AC, and there is no reason not to apply this to 300B or other similar tubes. The main difficulty there is getting it to operate stable into low power loads (there is a minimum load required, and some experimenting might be needed).

You can check out the RH813 on my blog for more info and some illustrations.
******

http://rh-amps.blogspot.com/

 

AC/DC, posted on October 25, 2014 at 11:21:57
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
" 'This is the reason why AC sounds better, the cathode being at the same potential.'

That statement confuses me. "

Ha, ha, you're not alone. That statement confuses me too, although maybe for a different reason. The problem for me is that there's no direct cause-and-effect link between "same potential" and better sound. No one I know of has yet demonstrated that elimination of the constant gradient across the filament is in fact the specific cause of better sound, much less offered a plausible hypothesis as to the nature of the relationship between the two. Does the filament gradient itself really alter current flow within the tube? If so, how? Until we know the answers to those questions, it must be assumed that DC supplies might be influencing the sound for another reason, one that hasn't yet been named or discussed.

All that aside, the issue you've raised appears to be related to the *average* potential that appears once we move away from the electrical center of the filament. In the DC model, the potential is greater on one side and less on the other. There's a constant gradient, which implies a constantly changing emission level as we move across the filament. With AC, the average is the same everywhere, promoting (in theory) identical *average* current draw from all parts of the filament. Whether this is the actual reason for differences in sound is anyone's guess. :)

 

RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 13:37:54
Tre'
Industry Professional

Posts: 17260
Location: So. Cal.
Joined: February 9, 2002
" With 5V DC across the heater, the midpoint is going to be at +40V while one end will be at +37.5V and the other at +42.5V (DC)."

And with AC heating, the midpoint is going to be at +40V while one end will be at +33V and the other at +47V, at least for a moment, each and every cycle.

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

 

RE: Is this regulated filament supply any good?, posted on October 25, 2014 at 17:22:12
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
That assumption about the regulator assumes that there's no cap at the output.

Your regulator has two caps at the output, which will act as a short to AC signal across the filament.

 

Yes..., posted on October 26, 2014 at 04:12:03
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
I have read about this before on your blog.

I think I will be gong this route one day.

Thanks for reminding me.

NC

 

RE: Is this regulated filament supply any good?, posted on October 26, 2014 at 04:25:44
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
Actually the cap across the output is the anathema feature of voltage regulators, according to the supporters of "fancy" solutions.

On the other hand, "fancy" solutions insist on NOT having the cap across the output (i.e. the filament) as the best feature of such solutions.

The A.M. "fancy" solutions operate as current regulators, but "take into account and set" adequate voltage as well. Those solutions are "voltage controlled current sources", known also as "current servo".

In my view, the cap across the output is not necessarily the reason why the regulator cannot cancel (affect) the music signal - rather the bypass caps from cathode to ground. This is particularly effective when bypassing is performed on each side of the filament (two caps, one from each filament/cathode pin to ground - instead of just one cap from "hudinger resistor" midpoint to ground).
******

http://rh-amps.blogspot.com/

 

But..., posted on October 26, 2014 at 05:01:47
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005

When you have no bypass caps (fixed bias), the cap across the filament is the only one left to avoid the regulator cancelling the music signal.

I wonder what happens if in this scenario you do remove the cap across the filament... Silence?

I have used VCCS solutions many times on DHT filaments using fixed bias, but the music signal was never cancelled.

NC

 

No, posted on October 26, 2014 at 06:58:52
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
To function correctly, the regulator must not be referenced to ground. Float the entire regulator so that it presents a high Z path to ground at the highest frequencies of interest, and the problem being discussed here will not exist.

 

So..., posted on October 26, 2014 at 07:04:30
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
Remove C4, C5 and D6?

A lot to contradictions in the answers of this thread. It looked so simple ;)

NC

 

RE:maybe mod these Ask TK, posted on October 26, 2014 at 07:56:59
amnesiac
Audiophile

Posts: 717
Joined: August 21, 2002
Thank you for your blog. I am going to need all the help I can get. I hope I can get this right. I hope someday soon someone makes affordable solder in modules for popular valves.

also Did you consider the earlier monster vt106 version of 813 tube? What a nice and still affordable tube.

 

RE: So..., posted on October 26, 2014 at 10:42:26
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
"Remove C4, C5 and D6?"

I should probably back up and ask whether you're using self bias or a negative bias supply. I assumed the former, and that the schematic you posted with the regulator grounded was just "boilerplate," but maybe that's incorrect.

In either case, it's not clear to me how the PS output caps will alleviate the issue of the DC (and therefore AC) gradient across the filament. The impedance of the filament in this mode is a little over four ohms (E/I). At 20 Hz, a 100uF cap exhibits about 80 ohms. That's not nearly low enough to smooth the AC induced across the filament. The caps are more effective at 1K and up, but perhaps modulation of the regulator by the low frequency energy creates intermod or other audible effects at those higher frequencies.

If you really want to use DC for this, I think the "voltage controlled current source" Alex recommended is the only option. I'm not familiar with the Coleman regulator, but it may also be appropriate.

Of course, this all changes if you're elevating the entire filament above ground with a bias resistor.

 

RE: So..., posted on October 26, 2014 at 11:28:36
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005

I use fixed bias.

I don't "really" want to use DC, but AC for the 10Y drivers of my amp doesn't look like an option from a hum point of view.

I will like in the Ronan Regulator or HF options again.

Thanks.
NC

 

RE: So..., posted on October 26, 2014 at 13:54:17
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
If you are using a 10Y as driver, standard AC is out of the question because of hum, which is going to be further amplified by the output stage.

At 7.5V and 1.25A this tubes is rather easy to do. Two tubes, one oer channel, will consume about 18.75W, thus you can use a 50W electronic transformer. After modifying the input diode bridge (added cap across and added NTC in series with the input to protect the input bridge from current surge - you should get slightly above 16.5V output. Now you can unsolder the secondary and split it approximately in half: assuming 9 turns secondary, you should get 1.83V per turn. Now you can use the same wire and turns as 4 for one tube and 4 for the other. The result should be 7.33V per tube, which I guess is just perfect. Carefully extend the secondary wires for each split, and fix the output transformer with some plastic string or similar. You are ready to go, it's as simple as that.
No hum, I guess you are not going to hear anything but music if the cap is approximately 300uF. Dead silent with no signal. As for the sound, cleaner than normal AC and more lively and detailed and fast than the best DC: also less noise/buzz/hum than DC.
******

http://rh-amps.blogspot.com/

 

Alex..., posted on October 26, 2014 at 18:23:28
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
Just to expand on what Alex is describing... You will need to be sure the electronic transformer (power oscillator) has a toroidal transformer at its output. The modules I've purchased in the past used miniature conventional transformers, much more difficult to modify (I wouldn't try). Searching eBay recently, I did find a few sellers that post pics of the inside of their modules, and several show a toroidal design in that position. Also, just to be clear, Alex is telling you to add a CT to the output transformer in order to power the filament. I assume the CT will be grounded, just as in the case of a 60Hz filament transformer.

Alex, I'm pretty sure you said recently that you've found some of the electronic transformers that are already designed to oscillate at 50 or 60 kHz. All the modules I've purchased ran at roughly 20 kHz, so I had to modify them. Can you point us to a specific seller for this? In my case at least, it would need to have a 120V primary, not 220V.

 

RE: Alex..., posted on October 26, 2014 at 22:31:13
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
TK, I have to correct one thing you got wrong because my explanation was not good enough: there is no CT but 2 separate 4 turn secondaries. The idea is to unsolder the output transformer from the board and split the secondary (assuming it has 9 turns) in half.

By splitting the 9 turns secondary you are going to "loose" one turn to the split, thus 2 halves with 4 turns each. Now extend those secondaries by soldering and isolating the joining points, so that you have longer wire to extend out of the original box: you should use stranded wire, not thick solid. Now solder the primary back to the board, leaving the secondaries "free" and protruding out of the box. You should fix somehow the transformer to the board, to make it a fixed assembly - I use plastic strips.

Thus each of the two secondary windings carrying approximately 7.5V HF AC is left floating and should be connected to the same pins where you would connect a normal AC secondary: a humdinger arrangement of fixed matched resistors is advisable, and bypass to ground is from the midpoint only: do not bypass both ends of the filament like you should do in a standard AC arrangement because to HF AC the cap is a dead short to ground!

The situation nowadays has improved as even the cheapest electronic transformers operate at 30kHz (my DMM cannot measure above 20kHz and they are sometimes declared as 30kHz, which is good enough for me).

Higher quality electronic transformers (branded) operate at 50-60kHz. Philips is one example. Most Philips and similar electronic transformers incorporate additional protection devices - no-load, shorted wires, overload) which are not vital but come in handy.

As for the output transformer, you need to check before ordering (look for pictures and even try to count the number of secondary turns)! There is little customization possible with conventional ferrite output transformer types, and lots of possibility with toroid cores.

Last but not least, check the specs for minimum load. And, obviously you must buy for your mains: 110/120 or 230/240V.
******

http://rh-amps.blogspot.com/

 

Just use Rod Coleman's regulators, posted on October 27, 2014 at 01:47:53
andy evans
Audiophile

Posts: 4369
Joined: October 20, 2000
Rod Coleman has been designing his regs for DHTs for several years and has gone through about 5 or 6 versions. They are a whole level up from Ronan Regs (hissy) and another world from LM317s. I can't see any reason not to use them for directly heated tubes.

The only other filament DC supplies I would ever think of would be choke input ones, maybe with more than one choke. Choke input gets you most of the way there.

Of course, the best solution is choke input followed by Rod Coleman regs, which is what I use. Hammond chokes have been cheap and very good for this. Perfect for 10Y, 26, 4P1L and those kinds of tubes. In addition those are tubes I always use in filament bias, which goes a whole step further in quality because you can eliminate the cathode bypass cap, and that's pretty important.

 

Where to order?, posted on October 27, 2014 at 02:42:34
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
Hi,

Where can I order these regulators. Google doesn't help me much. Does Ron has his own site? I'm a bit unable to find it.

NC

 

RE: Alex..., posted on October 27, 2014 at 03:46:46
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
Of course, the HF AC heaters supply can be used as well with fixed bias: only one side of the filament will be connected to ground (grounded), or even better in my view, the midpoint of the humdinger resistors arrangement will be connected to ground (instead of being connected to whichever cathode resistor or CCS might be used - which in turn is grounded on the other end).
******

http://rh-amps.blogspot.com/

 

RE: Just use Rod Coleman's regulators, posted on October 27, 2014 at 04:10:27
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
"I can't see any reason not to use them for directly heated tubes.

The only other filament DC supplies I would ever think of would be choke input ones, maybe with more than one choke. Choke input gets you most of the way there."

"My version" of the voltage regulator for DC heaters on direct heated tubes is extremely simple:
- low drop Schottky diodes forming a bridge
- one cap (let's say 4700uF or so)
- L4940V05 - a very-low drop fixed voltage (5V) regulator (1.5A max)
- another cap (let's say 1000uf)
and that's it.

The main advantage of this solution, which I tend to use from 6.3V AC outputting 6.3V DC (thus suitable for 6B4G, 2E22... and easily reduced via series resistors to 5.5V for 307A or 5V for 300B) is the fact that you can apply it to already existing transformer secondaries - and the low drop of both diodes and regulator also implies very low dissipation. Plus, the simplicity of the build is such that simpler is almost impossible.

Now for the sound - a DIY friend has compared this solution with the Coleman regulator, and has found that the difference in sound quality is minimal (might be even placebo, for that matter). I must add that he has tried standard AC as well, and while AC had unacceptable hum levels on his efficient speakers, he did not find AC sonically superior as well to "my" DC solution.

Now, why "not use..."?

1) Price (much more expensive than other simpler solutions) - which might be irrelevant to those who consider it sonically superior.
2) Heat (being a DC solution, it implies more power consumption, and more heat dissipation: some resistors have to be installed rather high above the board because they are going to get rather hot, etc.)
3) Last but not least, why not use a custom HF AC solution? Besides being cheaper, it will probably have lower hum/noise levels, and since it is AC, the cathode will be at the same potential throughout...

Just giving an opinion and a suggestion.
******

http://rh-amps.blogspot.com/

 

RE: Where to order?, posted on October 27, 2014 at 07:47:07
andy evans
Audiophile

Posts: 4369
Joined: October 20, 2000
Rod Coleman doesn't have a website. Easiest way to contact him is a personal message on DIY Audio where he's an active poster.

For example he contributes here to the 4P1L line stage thread
http://www.diyaudio.com/forums/tubes-valves/190857-4p1l-dht-line-stage-66.html

 

RE: Alex..., posted on October 27, 2014 at 08:53:24
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
I'm still not sure I understand the need to split the secondary. My 211s use fixed bias, and I simply apply the single secondary across the hum pot circuit. The center of that circuit is grounded, but as you say, neither end is bypassed. Thanks for the info on the newer supplies. I'll buy a few and see how they compare.

 

RE: Alex..., posted on October 27, 2014 at 10:02:57
Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000
Some years ago on this forum, Kurt Strain proposed the use of a transformer designed for fluorescent lighting that operates at very high frequencies, I think even higher than 60kHz, to run AC filaments. Am I remembering correctly? Does this make sense?

 

RE: Just use Rod Coleman's regulators, posted on October 27, 2014 at 10:51:36
I did a clone of the Colemanreg clone with a 2SC3852A CCS transistor and TIP121 for the buffer . To be honest with you I could not tell any difference whatsoever when taking the cathode connection from the 4P1L centre tap between using the whole Colemanreg or straight ring of two CCS . In future I will be just using the ring of two which simplifies matters and means the heatsinked CCS can easily be built skeleten-style and mounted from one of the loctal socket mounting screws

Al

 

RE: Alex..., posted on October 27, 2014 at 11:42:41
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
"I'm still not sure I understand the need to split the secondary."

The original secondary is probably 9 turns, for an output of 12V.
After installing the cap across the rectifiers bridge, the output is going to rise probably to 16.68V (this depends on various factors, but can be assumed as a rule of thumb to simplify the calculation).

Now 16.68V are too much for 10Y, aren't they? Instead of burning voltage across resistors (more unnecessary heat), and adding a second unit for the other tube, we can do a simple calculation: 7.5V + 7.5V = 15V.

This means that we already have the voltage and the space for two windings, the only thing we need to do is split the original winding into two (now separate) windings. While doing that, we are going to loose 1 turn, which turns out to be beneficial, since 16.68V/9 turns = 1.853V per turn.

This leaves us with 2 separate 4 turns windings, each of them will yield 4x 1.853V = 7.413V (which is an almost perfect approximation of 7.5V).

Not only have we avoided to burn voltage across resistors, but we are using the same original wire, which was good for 50W (i.e. 4.16A) so it must be more than good for our purpose (1.25A).

You could probably use the same 50W transformer for one 211, which requires 10V 3.75A -- in this case you would not split (i.e. cut in half) the 9 turns winding, but rather unwind the superfluous turns. Assuming the same unit and the same voltages, with 6 turns you are most probably going to get 11.12V - which is slightly too much for 10V, and thus would leave you with two alternatives:

1) Burn the excess 1.12V with resistors (0.3 ohm would suffice) which is rather easy to do, or
2) Count the number of turns on the primary and calculate how many do you have to remove in order to get as close to 10V as possible (usually 2 or 3 for Europe, probably 1 or 2 for US) by setting an adequate primary to secondary ratio.

Removing a couple of turns from the primary will not endanger the transformer. Take into account that we plan on using a 50W unit for 37.5W, so there is enough room to play and retain all the reliability.

NOTE:
In practice, most electronic transformers delivery slightly less than 12V, usually between 11.4 and 11.8 depending on the load - the higher the load, the less the output voltage. Since we are planning to use those units at less than rated load, their original output will most probably be 11.6-11.8V and from there should a precise calculation start. But assuming 12V instead leaves us in the worst case with slightly lower voltage, which is not going to endanger the tube: it is not so low to be considered as starvation, and when it comes to thoriated thungsten filaments, most are aware that 9.6 or 9.7V are a better option than 10.2V ...
******

http://rh-amps.blogspot.com/

 

RE: Alex..., posted on October 27, 2014 at 12:50:27
How well do these electronic transformers do with regards to the cold resistance of the filament ? I'd love to find a practical way of lighting up VT127 (5V 10A) . PC power supplies sulk and choke input choke smoothed supplies are too large to be practical .

Al

 

RE: Alex..., posted on October 27, 2014 at 13:07:58
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
When adequately "sized", they do absolutely perfect. The filament lights up effortlessly and reliably.

I have initially used higher quality 105VA units for each 813 (10V 5A). Higher quality units already include overload protection (they simply power down when overheated or overtaxed), short-circuit protection (they power down until the short-circuit cause is solved and removed), no-load condition (they simply do not turn on, although buzz can be heard from the inside of the units).

The second step was to use a 160VA unit for both tubes, and in the end I added another secondary to power the driver and CF tube (6.3V 1A approx.). The 160VA unit is a cheap but well made Chinese product and it powers everything up without a fuss, is rather cold in operation even after several hours, and has a very diminutive size.

You can see several illustrations on my blog - the small black box is the modified transformer with 3 secondaries... compare that to the size of (even) SMPS power supplies, let alone adequately sized power transformers, diode bridges, (someone mentioned chokes?!)... not to mention the heat dissipated by the regulators if you were to use them.

With all that, the most important feature is noise - I am unable to hear any. It's as "noiseless" as if the tubes were indirectly heated. Sounds almost too good to be true - but true it is.


******

http://rh-amps.blogspot.com/

 

RE: Alex..., posted on October 27, 2014 at 14:25:07
'Sounds almost too good to be true - but true it is.'

A potential 'iron-law' breaker . I like that :) Any suggestions on a unit that could do that 5V 10A filament ?

Al

 

10A Transformer, posted on October 27, 2014 at 20:28:08
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
A 10A filament will need a 160W transformer. You'll need to remove turns from the secondary of the output transformer to reduce it to 5V. You might also want to install a couple low value resistors to "trim" the final value (that's what I do in my 211 SETs).

I searched eBay for "160W electronic transformer" while writing this and came up with quite a few hits for 120V and 220V versions. Unfortunately, none of the listings show the inner workings, so there's no way to be certain if the output transformers are toroidal. On the other hand, none of them appear to be potted, so it's a simple matter to pop one apart and look. At worst, you'll lose $15 for your effort.

Just so you know, where Alex and I primarily differ in all this is the operating frequency. Alex is using newer transformers that operate at 30kHz or so out of the box. The transformers I modified years ago are running at 65kHz. Lynn Olson cautioned me at one time regarding the possible side effects of using such a low frequency (65kHz), and although they sound fine to me, I do wish they were operating at 100kHz or more. In fact, if memory serves, Davie Berning's amps use a minimum frequency of 250kHz. I suspect the upper frequency limit of these little transformers is determined by the capacitance of the active devices. Someday I'll revisit this, just to see if they can be made to do better.

 

RE: Where to order?, posted on October 27, 2014 at 20:33:35
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
Too bad he's not active over here. I really despise the administration style at DIY Audio. I cancelled my "membership" two days in.

 

RE: Alex..., posted on October 27, 2014 at 22:23:27
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
5V 10A is 50VA after all, so any unit capable of 50W should be able to do it: consider it a light bulb! In practice, I would suggest a 105VA unit for each or a 160VA unit for both 5V 10A filaments.

10A means thicker wire, but since you must use stranded or Litz, this translates to "bifilar wound" secondaries used in parallel.

For 813s, I ended up making 4 turns of 1.5mm2 stranded isolated wire for 10V 5A. For 5V 10A I would do just 2 turns and parallel the two windings for double current. On the primary side nothing changes, it's 50VA.

BTW, the VT127 seems to be 4V 1.25A, and indirectly heated at that? What is the direct heated tube that you are going to use with 5V 10A filament?
******

http://rh-amps.blogspot.com/

 

RE: Alex..., posted on October 28, 2014 at 07:29:20
Triode_Kingdom
Audiophile

Posts: 10011
Location: Central Texas
Joined: September 24, 2006
"5V 10A is 50VA after all, so any unit capable of 50W should be able to do it: consider it a light bulb!"

Amperage at the output transformer must also be considered. There's no way to know whether the windings of the 50W unit (~ 4A) can handle the increased current, or how the user will reduce the voltage. Rewinding the transformer is best, of course, but if a resistive drop is used, the 10A current draw from the smaller unit will overload it. That's why I recommended a 160W supply (13.3A) for this purpose. It's roughly twice the cost, but still very inexpensive. Incidentally, as a result of recent discussions here, I opened one of the 60W supplies that I had purchased last year as a spare. The output transformer is conventional, not toroidal, much more difficult to rewind.

 

RE: Alex..., posted on October 28, 2014 at 14:18:43
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
If we consider the option to use original secondary wire, we need to provide a 160W unit like you're suggesting. If the amp is stereo, we can use it for both tubes, as 2 secondaries, as explained for 10Y and the 50W unit.

While cheap, it is not at all necessary to use a 160W unit to power a 50W load. If the secondary is removed and a new secondary with adequate wire is wound instead, a 105W unit is literally twice as powerful as needed. Besides the fact that there is no need to burn voltage across resistors (low values of discrepancy can be adjusted by unwinding a few turns from the primary), you would have to burn a lot of W to overload the unit! At 10A, .5 ohms is already 50W, so why throw away all that power and have to deal with huge dissipation? That's what got me to get in the HF AC story in the first place: unnecessary losses in power consumption and heat dissipation - so why would I get back to that once I took a different road?

Once you make it possible for 2x 50W of heaters and a few more W for the drivers to be effortlessly produced by a rather cold (40 degrees C after several hours of operation) and small box... you just cannot get back to burning excess voltage in heat.

As for 50W, imagine 2 "normal" mains transformers. One is 10V 5A, the other 5V 10A. They would be identical size, wouldn't they? The difference would be in the secondary wire thickness and turns number... but if we assume the transformer secondary is bifilar, 2 secondaries of 5V 5A each, than you can do both options with the same transformer. In series 10V 5A, parallel 5V 10A. It's literally as simple as that. The same is valid for the HF AC output transformer, only the size is very much different, as well as the type of wire used (both are frequency dependant).
******

http://rh-amps.blogspot.com/

 

Page processed in 0.038 seconds.