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[jane]

And as promised, the schematic. If you have any questions, do not hesistate to ask.

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

Any reason why Rg (EL84) is as low as 39k? Together with the 22nF coupling cap this will make a low cut filter in the audio band and the load line for the 12AX7 will be quite steep.

 

[mhouston]

Any reason why Rg (EL84) is as low as 39k? Together with the 22nF coupling cap this will make a low cut filter in the audio band and the load line for the 12AX7 will be quite steep.

I'm with jane. I would think 390K may be better.

 

[tipetu]

Oh, I never thought of that. Dont ask me why it`s 39k. Thanks for the tip, I`ll correct it.

 

[tipetu]

Damn that made a difference haha. Thanks!

 

[artosalo]

I earlier represented some photos of the prototype of this amplifier and now it has reached pre-production stage.
This is a 2 x 10 W PP with Tesla QQE03/12 tubes.

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

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

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

 

[mhouston]

Looks very pro. I have not heard of the tubes before.

 

[Junm]

that QQE3/12 dual tetrode tube looks like 6R2P of soviet...dual tetrode too with lower Pd and has flexible leads....nice work..

 

[ChrisA]

I earlier represented some photos of the prototype of this amplifier and now it has reached pre-production stage.
This is a 2 x 10 W PP with .....

I'm building something like that too.

Here are some photos that show my construction method. A power supply board is shown. Also I just finished the major metal work for the chassis and I'm test fitting it inside the main part of the cabinet. So far so good. More work to be done but now I know the bolt holes line up and the chassis fits.

https://www.dropbox.com/sh/vspqq9fbsptuoq9/6xIQUgVkhj

 

[artosalo]

that QQE3/12 dual tetrode tube looks like 6R2P of soviet...dual tetrode too with lower Pd and has flexible leads....nice work..

Actually GU-17 from soviet era should be similar to QQE03/12, but my tests with GU-17 tubes showed much different performance.
To get 10 W out with 300 V anode voltage reguires screen voltage up to 260 V which is essentially beyond the specs. In this case the screen current is also very high. GU-17 was a disappointment to me.

 

[soundbrigade]

I have made a stereoamp with two tubes, one is a 12AT7 and the second a 5998A. Dual powertubes are great, or at least can make interesting projects. I am fiddling with one 832 but have cast glances on some obsolete Russian 6R3S from my Priboj. Each tetrod in the tube is rated 20W.

 

[mhouston]

I have made a stereoamp with two tubes, one is a 12AT7 and the second a 5998A. Dual powertubes are great, or at least can make interesting projects. I am fiddling with one 832 but have cast glances on some obsolete Russian 6R3S from my Priboj. Each tetrod in the tube is rated 20W.

I usually see you on diyaudioprojects. Do you have an image of the tubes?

 

[soundbrigade]

OK, here's the 5998A:

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

Not finished but this will be my 5998A PSE:

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

The Russian dual powertetrode looks like this. Socket is the GU-50 type socket:

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

 

[artosalo]

Is there sufficient gain with one 12AT7 combined with low mu 5998A?

Your Priboi pcb looks more than typical with burned resistors and circuit board .

One douple tetrode that I like is GMI-6. It gives 20 W with very low distortion in pp-mode.

 

[soundbrigade]

5998A is very much like 6AS7G, but has higher gain, but the 12AT7 handles the tube most perfectly.

I had the Priboi rebuilt but will some day rebuild it again and throw in, either a bunch of GU-50, or 6P36S (EL500) or maybe just some 6L6.

 

[artosalo]

If you change the output tubes to GU-50, then take the supply voltage for the phase splitter/amplifier tube (6N6P) from 420 V line. With original supply voltage the swing of the phase splitter is far too low for GU-50.
One of my friend just modified one a couple weeks ago.

 

[soundbrigade]

I used this schematic for the modification:
http://www.pastisch.se/tubes/images/Priboj_sch.jpg.
Have to re-wire the power tranny.

 

[vitalstates]

finally got this off the breadboard and into a box..after nearly 5 years...

Vitalstates- Amplifiers

 

[mhouston]

vitalstates: really very nice. To go to the effort of painting the Hammonds is a fine touch and looks like an excellent heavy paint job on chassis etc.

 

[richwalters]

finally got this off the breadboard and into a box..after nearly 5 years...

Vitalstates- Amplifiers

........and underneath looks ?

 

[vinylkid58]

OK, here's the 5998A:

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

S&M Rubber Duckie looks like he's in love.

jeff