PP GU50 triode strapped project

[FrançoisL.]

Gentlemen,

Here's what brings me here.
I have been living for 5 years with a Leak ST20 amplifier that has given me a lot of satisfaction.
I have modified it quite a lot though keeping its original spirit (split PSU and put choke instead of resistor in Pi filter and input sensitivity lowered).
Last modification was to triode strap the power valves and once you have tasted triodes, difficult to go back to pentode
But, because there is a but, I now feel that i would enjoy a little bit more power.
My speakers are rated 91db.

That is why, I was thinking to make a GU50 based amplifier.
My idea is to make a PP but with the GU50 triode strapped.

I have searched a lot regarding such a configuration but I must admit that I have found almost nothing in regard.

Could someone in the audience "take my hand" (as I am some kind of novice in amplifier design) and help me with this project?

Kindest regards,

François

 

[matejsirk]

Hi,
how much power do you need? You can easly squeeze more then 6W with GU50 in SE (triode) or up to 15W (pentode).

 

[revintage]

Hey François,
I hope you know that GU50 is rather unlinear as triode. There was a thread here about trioded GU50 not long ago. Have you really tried the "search-function?

 

[FrançoisL.]

Hi,
how much power do you need? You can easly squeeze more then 6W with GU50 in SE (triode) or up to 15W (pentode).

I would need around 20W thus the idea of triode PP.

 

[FrançoisL.]

Hey François,
I hope you know that GU50 is rather unlinear as triode. There was a thread here about trioded GU50 not long ago. Have you really tried the "search-function?

Lars,

I have indeed browsed the forum and though, I would like to experiment triode PP GU50

 

[matejsirk]

Lars,

I have indeed browsed the forum and though, I would like to experiment triode PP GU50

I found this two schematics on net:

 

[FrançoisL.]

I found this two schematics on net:

Very kind of you
Do you have the link to these schematics?
And if you understand Russian, what is written on?

 

[Wavebourn]

I found this two schematics on net:

I would suggest to go for it: all schematics published by Sergeev are carefully designed and well tested in real life.

Hey François,
I hope you know that GU50 is rather unlinear as triode. There was a thread here about trioded GU50 not long ago. Have you really tried the "search-function?

Hi Lars;

a first, he wants PP. And second, even though Gu-50 is less linear as triode that I would like for SE, anyway it is more linear than 6L6 clones that are used widely, including in SE amps.

 

[FrançoisL.]

I would suggest to go for it: all schematics published by Sergeev are carefully designed and well tested in real life.



Hi Lars;

a first, he wants PP. And second, even though Gu-50 is less linear as triode that I would like for SE, anyway it is more linear than 6L6 clones that are used widely, including in SE amps.

Hello Anatoly,

I have read quite a lot of your GU50 realizations, thumbs up!

of the two schematics by Sergeev, which one would be your favourite, if any?

 

[revintage]

Hey A,
The bad stuff shouldn´t be the yardstick. About PP 3rd harmonic doesn´t look 100% good either.

 

[costis_n]

Hello Anatoly,

I have read quite a lot of your GU50 realizations, thumbs up!

of the two schematics by Sergeev, which one would be your favourite, if any?

Although I was not asked, I vote for the one on the left, because there is one capacitor less in the feedback loop = more stable.

 

[Wavebourn]

Hey A,
The bad stuff shouldn´t be the yardstick. About PP 3rd harmonic doesn´t look 100% good either.

Lars;
3'rd harmonic means drive over symmetric bending of the curve. Shift bias point and you have less of it, but more of 2'nd order one. For 6L6 to shift bias in similar to Gu-50 region means instant death from 150W dissipation. I have somewhere one nice datasheet for 807, it is quite revealing.

First my Pyramid I tried to make using 6L6 tubes. It was quite nice, but I had to use 4 tubes for 40W of output power, otherwise it was far from high-end. Then I tried Gu-50 and got 80W of nice high-end power from one pair.

Everything is relative. When I say that 4P1L is much better for SE that Gu-50, it is a comparison, It does not mean that Gu-50 is bad for SE. But when I said that Gu-50 is much better for SE than KT-88 I don't mean that KT-88 is bad tube. Some people enjoy SE amps made on KT-88 and similar tubes, even 807. 807 looks like a lady, while Gu-50 looks like a trashcan. Some people prefer to sacrifice look to voice, some prefer to sacrifice voice for look.
I would be happy to see tubes similar to Gu-50 in sexy bottless, with half longer electrodes for more power and lover output impedance. It would literally kill all known tubes.

 

[Wavebourn]

Hello Anatoly,

I have read quite a lot of your GU50 realizations, thumbs up!

of the two schematics by Sergeev, which one would be your favourite, if any?

Thanks;

I would prefer the left one; on clipping it's phase splitter would sound less nasty.

 

[FrançoisL.]

I would prefer the left one; on clipping it's phase splitter would sound less nasty.

Though, regarding the right one, the one with 6H3P, Sergeev says:
"simplified scheme and this had a positive impact on the sound. Changed the first stage and phase splitter.
Surf phase splitter scheme, but with a larger supply voltage. The second and third grids are connected to the anode, as recommended by A.Rezvoy to reduce the internal resistance of the tube."

BTW, what does the google translator translates by "surf phase splitter"?

 

[Vincent77]

That's a concertina (cathodyne) phase splitter.


Is connecting the suppressor grid to the anode a good idea? In a triode-strapped pentode, I mean.

 

[FrançoisL.]

That's a concertina (cathodyne) phase splitter.

Merci Vincent

 

[jane]

Here is my version of GU-50 PP triode:

An externally hosted image should be here but it was not working when we last tested it.

Single ended driver stage and cathode windings to keep the output impedance low (enough) without the means of gNFB.
Should be finished during the summer..

 

[LAZAROIU]

Gentlemen!

We propose a schematic quality with very good results and audiofile.
The assembly is practical and simulated but with LTC, the results are execelente.
Also proposed by comparison and all tube schematic GU50 pentode mode but of course the power will be higher.
If the schematic GU50 triode mode, power is less than 18W ... 22W, but the qualities of a triode.
OT is the type McIntosh, recalculated and designed by me, the practical is very easy.
Sorry for English, but I translated <google translate>.
Thank you.
*******************************************************


GU50 tubes are excellent, but they should be paid attention ...

 

[Wavebourn]

I like them all. Good choice of schematics! You have to try each one François, then decide which you prefer.
But I personally like 3 last schematics more than both Sergeev's schematics: coupling capacitors from drivers to grids of output tubes is evil.

 

[FrançoisL.]

I like them all. Good choice of schematics! You have to try each one François, then decide which you prefer.

Well, one of the three is pentode, so "only" two left

But I personally like 3 last schematics more than both Sergeev's schematics: coupling capacitors from drivers to grids of output tubes is evil.

There is maybe a way to modify that?

@LAZAROIU: in your triode strapped schematics, you use ECC85.
Would there be a Russian equivalent that could be use in place of them? I have plenty of Soviet double triodes but no ECC85.....