Tube Power Supplies a Different Approach!

[stanbp64]

Lot of good info here from everyone..... just wish i understood at least half of it. Does open up alot of areas to experiment though. Keep it coming:yes:
stan

 

[Dave C]

Lot of good info here from everyone..... just wish i understood at least half of it. Does open up alot of areas to experiment though. Keep it coming:yes:
stan

Me to stanbp64, I know what I like and I have that at this point in my 300B's.
Tonight I listened to some CD's in the workshop through my Sansui 1000A. I use it several times a week. By all estimations of this discussion that amp has a poor power supply, but boy does it sound smooth. Because of that I'll not touch that power supply until I have to!

 

[hotroady]

Me to stanbp64, I know what I like and I have that at this point in my 300B's.
Tonight I listened to some CD's in the workshop through my Sansui 1000A. I use it several times a week. By all estimations of this discussion that amp has a poor power supply, but boy does it sound smooth. Because of that I'll not touch that power supply until I have to!

Now, you are talking very nice trannys and the heart that pumps life to everything. It's an inherent advantage. Makes me wonder how Kegger's brew sounds!

 

[Dave C]

Makes me wonder how Kegger's brew sounds!

I have to get on Kegger every once and a while for scrapping out those 1000A's. Man I wish he wouldn't do that! (just kidding Kegger!)

 

[hotroady]

My thinking is that vacuum tube technology got cut off by transistors just when it was really starting to take off. They were just starting to do some cool stuff with compactrons, like add caps and resistors to the inside stuff. The other thing is, that 90% of all commercial (and most home brew) amps are one of three or four basic designs. This is part of what makes tubes so much fun to experiment with to this day. Thinking outside the box is very easy to do, and sometimes gives surprisingly positive results.:yes:

I have to agree. My Puresonic Quadramatic Model 112 pre uses Compactrons. All triple triode. The Puresonic Quadramatic uses 2 Mullard 5AR4 in parallel for rectification. 4 12ax7's in parallel acting as one huge triode. It was made to compete heads up with Marantz 8b. My tech and his brother have close to 100 yrs experience between them. His Holy Grail is the Marantz 8b, he finally admitted, that he thinks the Puresonic has an unmatched "certain presence" and he likes it better. It's stone stock, with 40 cans replacing stock 60 cans. 181 damping factor! Superb bass. Want to replace some of the 1965 caps..kinda expensive because twice as many as normal. There ain't no way in hell I'll ever let go of this 'dynamic dou'

 

[hotroady]

I have to get on Kegger every once and a while for scrapping out those 1000A's. Man I wish he wouldn't do that! (just kidding Kegger!)

I bought a set a while back off Epay. Someday I want to build me an amp with these! A blind man turned me onto the 1000A and Klipsch, about 38 yrs ago. He did some incredible feats with his hearing ability. He could usually tell you exactly what car pulled up next to you at an intersection, by exhaust tone. He also feed wire up through a 1 inch conduit through a floor, first stab via sound of voice from the above floor! I was very interested to know what Mark listened to.

 

[SET12]

All I can tell you is a 5v change in a EL84 or 6V6 can and at times has had a giant difference in sound. (just did it a week ago)
(so for me the clipping of that resistor does not make the pilot amp a good example) (these tubes like increased voltage a lot)
(now it's within reason the voltage increase, more noticeable at the low end and less at the high end of the scale as well here)

Lets put this a little differently!

Did you do this voltage change by changing the bias? Or did you do it by taking some supply resistance out?

I know from studying Tom Mitchell's "The audio Designers Tube Register" that by changing the bias is going to effect the rp of the tube and the transconductance. But I can tell you this, it is not much at all in percentages.

When I designed my phono I played with this a lot!

Now change "R" in a supply path especially with high volume currents and it can be very dramatic IMO.

Using a 100 ohm in a supply path feeding a 100uf cap is a time constant of .01us feeding it with a 1 ohm is .0001us!

This a speed factor of essentially 100X

Changing a tubes Plate operating conditions by a few volts changes the the transconductance or rp by fractions and small at that!

I will say the effect of 100 ohms in the path of a small signal tube is nil!

And thats simply because moving 5-10ma does not contain the energy that 100ma's plus has when it comes to charging and discharging. "Basically moving energy in volume from one point to another!"

Variables would have to be the same on each supply, same capacitance, same voltage, same power tranny, same rectifier and the same stages of filtering, unfortunately you can't get that same voltage with the same power tranny with and without that resistor in there.

Even with the voltage changed, the energy of the supply for both 100uf caps would be a total of 9.3 joules @ 300VDC separated (4.5 and 4.8 Joules) vs 9.6 joules @ 310VDC combined.

Granted the resistor was taken away and you now had twice the reserve that the output stage ran on.

So you think doubling the energy reserve was the factor? I don't think so!

How do I know! I added 4x more poly props to my final supply stages of my mono's nothing else changed! not even the voltages. Did I hear anything substantial!? I'd say a subtle difference in weight just!

But it was nothing like the pilot!

So as I said, to many other variables to just say it was the less resistance that made that huge impact there.(the power supply voltage went up as a whole, including the voltage to the driver tubes, which would have an impact here to)

Again, I'm not saying what your doing isn't working for you, but the Pilot example just doesn't cut it for me.

As I said before from Tom Mitchel's work, its nil on rp and transconductance.

And as said before its Transconductance X Load that generates dynamics. There are other variables for dynamics as well but nothing changing other than rp and Gm essentially the dynamics remain the same IMO. And if you did hear something it would be subtle IMO.

Nothing like the 100R removed from the Pilot!

If I saw a swing that was a high percentage like 20-50% or something I might buy into a 5-10 volt change.

But as Tom Mitchel's work points out its a very small change.

I might add that DCR within a pi filter just isn't limited to a supplies caps and resistors or chokes for that matter!

But the Power Transformers DCR path itself is a factor as well IMO.

And there are other locations that DCR affect sound as well!

:yes: There are variables to

Cheers :thmbsp:

SET12

 

[SET12]

Me to stanbp64, I know what I like and I have that at this point in my 300B's.
Tonight I listened to some CD's in the workshop through my Sansui 1000A. I use it several times a week. By all estimations of this discussion that amp has a poor power supply, but boy does it sound smooth. Because of that I'll not touch that power supply until I have to!

Dave,

I had a discussion with a Tech, Dennis Had of Cary Audio is no fan of voltage doubler's He has had an influence on my work as well.

But the as the Tech pointed out, the transformer used as doubler has half of the winding resistance as a center tap!:scratch2: Something I didn't think of!

It would be cool if you could measure the DCR of the Sansui B+ winding:yes:

There is also I see, a resistor in line before the diode! I wonder if you could measure that as well! or maybe its clearer on your schematic.

One other thing not to forget here! The Sansui 1000A's output stage runs directly off its rectifier:thmbsp:

SET12





Again Dave, Great work on those amps of yours

 

[Kegger]

Voltage change was from going from a 5uf input cap to a 15uf input cap, voltage
raised 7v, and a drastic change in the performance of the amp, from say 250v to
330v EL84's an 6V6's respond a fair amount to voltage increases, I found this out
some time ago with multiple amps. (also they don't like low screen voltage either)

I use decent size capacitive tanks on the section feeding my outputs, this makes
a stiff supply that does not sag/drain the caps on transients, upping that amount
on a vintage amp that usually has small capacitance there's usually a big upgrade.
(generally has a larger improvement on the bass and authority of the amp)

I generally use "higher" GM tubes with lower plate resistance in my designs as well.

Also I find a lot of vintage amps the drivers are starved of both voltage an current
so upping there voltage to them is usually a bonus as well, running a driver on less
then 100v is quite common and I've found just getting it over the 100v mark is the
place they start to open up an perform better. (different tubes different voltages)

 

[jon_s]

But the as the Tech pointed out, the transformer used as doubler has half of the winding resistance as a center tap!:scratch2: Something I didn't think of!

Actually, it's more like 1/4th, since the transformer will be designed for equal power dissipation. In practice, the doubler works much like the bridge-rectified (or conventional full-wave) supply, except with a safer secondary voltage and series caps on the input. In the 400+ volt range, there are many advantages, and it should be a more-reliable solution.

 

[Squidward]

Thank you jon_s, good food for thought!

 

[Dave C]

SET you need to get over here so we can go over some of this stuff. If I'm casually listening to music while working on a different project the Sansui is the ticket. It is sweet mellow and never edgy. On the other hand sitting down in the living room and listening to the 300B's through the Klipsh speakers is a real "front row" concert experience type of thing.
For those that missed my 300B thread on DIY this is the link.
http://www.audiokarma.org/forums/showthread.php?t=224767&highlight=300b+set
Scan down a few posts and you'll see pictures on the finished projects.

 

[Dave C]

Congrats Dan on starting and maintaining a great thread!

 

[SET12]

Actually, it's more like 1/4th, since the transformer will be designed for equal power dissipation. In practice, the doubler works much like the bridge-rectified (or conventional full-wave) supply, except with a safer secondary voltage and series caps on the input. In the 400+ volt range, there are many advantages, and it should be a more-reliable solution.

Thank you, jon_s

Yes, as far as a full secondary DCR of a center tap design.

And yes you are correct it would be 1/4 the DCR for a non center taped tranny being used as a voltage doubler that achieves the same voltage as a center tap design. From end winding-center tap-to end winding

But in actuality, the center tap design uses only one side of itself at a time!

So a doubler offers 1/2 of the DCR in contrast to a center tap design.

Here's a reference link

http://www.play-hookey.com/ac_theory/ps_rectifiers.html

From the link

Full Wave Rectifier

"While the half-wave rectifier is very simple and does work, it isn't very efficient. It only uses half of the incoming ac cycle, and wastes all of the energy available in the other half. For greater efficiency, we would like to be able to utilize both halves of the incoming ac. One way to accomplish this is to double the size of the secondary winding and provide a connection to its center. Then we can use two separate half-wave rectifiers on alternate half-cycles, to provide full-wave rectification. The circuit is shown above.

Because both half-cycles are being used, the DC component of the output waveform is now 2vp/π = 0.6366vp, where vp is the peak voltage output from half the transformer secondary winding, because only half is being used at a time."

There are some other issues with a doubler here.

http://sound.westhost.com/power-supplies.htm#doubler

Going back to the first link there are some alternative voltage doubler circuits worth looking into IMO.:scratch2:

Cheers :thmbsp:

SET12

 

[SET12]

SET you need to get over here so we can go over some of this stuff. If I'm casually listening to music while working on a different project the Sansui is the ticket. It is sweet mellow and never edgy. On the other hand sitting down in the living room and listening to the 300B's through the Klipsh speakers is a real "front row" concert experience type of thing.
For those that missed my 300B thread on DIY this is the link.
http://www.audiokarma.org/forums/showthread.php?t=224767&highlight=300b+set
Scan down a few posts and you'll see pictures on the finished projects.

Congrats Dan on starting and maintaining a great thread!

Thank's Dave,

Glad your enjoying the thread!

Yeah, I'd love to get to your place, you have a lot of nice toy's

If only work would stop forcing me to work six days a week :tears:

:scratch2:I guess I have a job though

 

[SET12]

Voltage change was from going from a 5uf input cap to a 15uf input cap, voltage
raised 7v, and a drastic change in the performance of the amp, from say 250v to
330v EL84's an 6V6's respond a fair amount to voltage increases, I found this out
some time ago with multiple amps. (also they don't like low screen voltage either)

From a 5uf to 15uf a voltage increase doesn't surprise me that there would be an increase in voltage.

Yes, I'd agree 250VDC is on the low side and I wouldn't disagree that the 330VDC wouldn't have some heft.

I use decent size capacitive tanks on the section feeding my outputs, this makes
a stiff supply that does not sag/drain the caps on transients, upping that amount
on a vintage amp that usually has small capacitance there's usually a big upgrade.
(generally has a larger improvement on the bass and authority of the amp)

I generally use "higher" GM tubes with lower plate resistance in my designs as well.

Yes, absolutely larger supply can do wonders.

Yes, I like them high Gm tubes as well but I also love a few that are not like the 12BH7,6CG7,6EM7.

Also I find a lot of vintage amps the drivers are starved of both voltage an current
so upping there voltage to them is usually a bonus as well, running a driver on less
then 100v is quite common and I've found just getting it over the 100v mark is the
place they start to open up an perform better. (different tubes different voltages)

Yes, I know what you mean I run my 6EM7's on my SET amps with a 500 volt supply which puts 300VDC on the plates.

Very good Kegger:thmbsp:

SET12

 

[SET12]

Could you run the amp with the resistor, record the B+ voltage, then clip the resistor and run the amp on a variac to get the same B+? Would that be a better test? All this talk about tubes liking higher voltages has me thinking about 6CA7s. They are rated at 800volts (plate), and most amps barely run them at half that. ??:scratch2:

One of my friends has a CJ Premier 1 and 2, His power amp was switched from 6550's to EL34's but after going thru hell with the 6550's which he down right deplores from screens arcing over and such he just loves his 6CA7's.

He also loves KT90's as I do and of course the KT88's are a fav of mine. My least favorite is the 6550.

Yep, and this is the problem with "most" mods. It's very hard to A/B stuff. I mean, how many people have configured an amp with a switch to change between Riken or Allen Bradly resistors, so they could be properly A/Bd? Nobody that I know of. I guess that why shiny stuff sells so good to mod freeks. It seems like the longer I'm in this hobby, the less shiny stuff I'm buying.

I especially like this post of yours :yes:

As you may or may not know I use outboard crossovers that allow quick changes of its components in a matter of a couple of minutes.

I can change out inductors, resistors, and caps with ease.

Yes, I have heard a few resistors namely the ones in my crossovers!

One of my most astounding changes was changing a 40 ohm resistor that was in parallel with my Crites tweeters on my Klipsch Fortes.

Ohmites vs Duelunds!

The Ohmite was a favorite of North Creek Music as they voiced out nearly 20 companies. They prefer a resistor that has a low temperature coefficient as they found they could hear thermal transient suppression I believe.

Well, I subbed in the Duelunds and I was shocked at how much smoother they are! They have a negative temperature coefficient! Allowing for greater dynamic response. They are made with graphite, but what I can't get over is that they are not even in the signal path and these things are just tremendous. They are intended for crossovers. But I have given thought of using them in self bias power tube circuits.

So IMO they are way ahead of any competition I have heard.

Their caps are just as amazing! And so are their prices! the resistors are more manageable and arguably perhaps some of the best in the world IMO.

Now there's my amps, nothing is shiny there! Just the warm glow

SET12

 

[GordonW]

One of my friends has a CJ Premier 1 and 2, His power amp was switched from 6550's to EL34's but after going thru hell with the 6550's which he down right deplores from screens arcing over and such he just loves his 6CA7's.

He also loves KT90's as I do and of course the KT88's are a fav of mine. My least favorite is the 6550.

Problem's not the 6550... at least it's not a fault of the tube ITSELF.

It's the fact that the CJ amps are running the screens at nearly 600V (around 575V on most)... on a screen rating of only 400V on the 6550!

These amps should have been specified for KT88s from the beginning... 800V plate, 600V screen. Also with enough plate dissipation that you can bias them up rich, and still not red plate (35W for the 6550, 42w for the KT88).

The EL34 will "get by" if you bias it low enough (also rated at 600v screens)... but the REAL solution is the KT88. Or the KT90, as mentioned... it will also readily handle the screen voltage (rated 600v on the screens)...

So, it's silly to blame the 6550 tube... when the manufacturer knowingly built the amp where it was running it outside of spec...

Regards,
Gordon.

 

[Kegger]

Same thing with a lot of VTL amps.

I redid one a bit back that was running 600v on both the plate an screen using EL34.

Yah it worked but would eat tubes an only certain brands would take it, It was fixed
bias so all the voltage was on the tubes, I modded it for cathode bias and left just a
touch of adjustable bias left to balance the 4 tubes, now it runs KT88 at roughly say
550v plate to cathode, much safer operation, also now triode instead of pentode.

 

[SET12]

Problem's not the 6550... at least it's not a fault of the tube ITSELF.

It's the fact that the CJ amps are running the screens at nearly 600V (around 575V on most)... on a screen rating of only 400V on the 6550!

These amps should have been specified for KT88s from the beginning... 800V plate, 600V screen. Also with enough plate dissipation that you can bias them up rich, and still not red plate (35W for the 6550, 42w for the KT88).

The EL34 will "get by" if you bias it low enough (also rated at 600v screens)... but the REAL solution is the KT88. Or the KT90, as mentioned... it will also readily handle the screen voltage (rated 600v on the screens)...

So, it's silly to blame the 6550 tube... when the manufacturer knowingly built the amp where it was running it outside of spec...

Regards,
Gordon.

That was his trouble not mine as I have never owned a 6550 amp. Of all that I have heard I only ever heard one that sounded really impressive to me as most have always sounded stressed to my ears.

But no wonder with a maximum of 400 volts listed for the tubes maximum design center for its screens I can see why he had the issues, geez. GJ runs em to hard and many other amps within their line have the same issues!

I haven't had to repair any 6550 amps, but I'll remember it now!

Thanks for pointing it out!

Same thing with a lot of VTL amps.

I redid one a bit back that was running 600v on both the plate an screen using EL34.

Yah it worked but would eat tubes an only certain brands would take it, It was fixed
bias so all the voltage was on the tubes, I modded it for cathode bias and left just a
touch of adjustable bias left to balance the 4 tubes, now it runs KT88 at roughly say
550v plate to cathode, much safer operation, also now triode instead of pentode.

Nice work Kegger!

SET12