www.wavebourn.com

Hello to everyone

I am French. But I will see a doctor to treat me !

I'm part of a forum for DIY http://www.elektor.fr/ and Francis Ibre is a great help to me, but I cannot monopolize all of his time for me.

I have read many many page, here, on the GU50 but I can't find what I'm looking for.
I would like to make an amp PP 50-80 W UL. I'm ready to do a report on its implementation, on this forum and that of elektor, to help newbies like me.

I am looking for a diagram that has been proven (the pyramid looks very well!) with references to the Transformers from output to order, the bias setting, some values of voltage to verify my prototype.

If I not understand the curves of the tubes, I know read a schema and realize it.

A brief overview of some achievements (thank again Elektor for his help): http://moxalain.fr/haute-fidelite.html

Best regards
Alain
Bordeaux - FRANCE

It is not a good idea about UL amp with Gu-50. The screen grid is quite dense, so you can't use anode voltage above 300 Volt, as the result the tube will be under-powered.

Look at Pyramid schematics, I used there feedback from anodes to first grids of Gu-50 tubes. It is better than UL with feedback to screen grids. More flexible, more linear, and you can get lower output impedance, lower distortions and higher power such a way.

Thank you Anatoliy,

Do you have a link on the page, the references of the EDCORs so I order?

Where do the point 1 go (it is so confidential ?), it's feedback (only R ?) to the transformer secondary I think. 16 Ω ?
2 & 3 to Output stage. OK

Thank you for taking the time to answer
Best regards

Point 1 is feedback, from 8 Ohm tap of secondary. Yes, R only. All that dances around square waves are silly: if to shunt feedback resistor by cap you need to increase time constant in dominant pole compensation for stability, not worth it.

Yes, 2 and 3 go to output stage, to the same points go parallel feedback by voltage from anodes of Gu-50 tubes.

I ordered custom transformers from Edcor. 2x285 V secondary for B+, 66V for bias, 2x12.6 V for filament. One 12.6V is split on 2x6.3V for 6E1P filaments.
Gu-50 filaments are powered from 12.6V windings, 2 tubes per each. They are interconnected, and used with Shottky double diode. Stabilized 12.6V powers filaments of small tubes, pairs in series.

Output transformers should have 8-10K P-P primary. Mine had 10K, and 4-8-16 Ohm secondary. Now I am going to order 8K primary transformers. They are rated for 20 Hz - 20 KHz on full 100W power.

Input goes to LDR through 10K resistor. Also, balanced input transformer is not drawn since the software that I used refused to draw more components for free.

With 6F12P tube sensitivity was a bit too much. With ECF200 it was fine, but they require 10-pin sockets. Now I am going to use 6F1P - it is very nice tube, real high - end sleeper.

Good Perfect

Thank you so much

You are welcome!

Let me know how it sounds.