Help with these Russian GU50 tube amplifier

[gaborbela]

Hello

I like these amplifier a lot.
But because is posted in Russian website even if I translate with translator hard to understand everything.
It would be stupid to start a project and I do not understand all.
Îäíîòàêòíûé óñèëèòåëü íà ÃÓ-50
I would like to ask some help from Russian DIY-ers.
Even at the schematic some writing I do not understand.
Also there is some type of transistor, I don't know what type or part number.
Also I attache the schematic.
If I understand well the 420V goes to left chanel and right chanel
Also the bias goes to left chanel and right chanel BUT on the schematic each chanel has two bias- do I have to connect that two together??
There is 30V at the PS, I have no idea where it goes.
Any help it would be great , otherwise I have to look for other GU50 project.
These would be great with the 25W Edcor OP transformer.
Thank you very much

Greetings gabor

[Timofey]

>>Also there is some type of transistor, I don't know what type or part number.

"Transistor" is Filter+delay turn on circuit.
See attach UZF

>> If I understand well the 420V goes to left chanel and right chanel
Yea, you are right.

>> Also the bias goes to left chanel and right chanel BUT on the schematic each chanel has two bias- do I have to connect that two together??

Yes, you have to connect bias inside of each channel together. Also bias for channels separated.

>> There is 30V at the PS, I have no idea where it goes.

+30V applayed to filaments for AC "Hum-m-m!" noise cancellation. Just solder together points "A" on PSU schematic.

[Jaap]

What is the impedance of the OPT ?

[Timofey]

3200-3300 Ohm / 8 Ohm

[Timofey]

>> >> Also the bias goes to left chanel and right chanel BUT on the schematic each chanel has two bias- do I have to connect that two together??

>> Yes, you have to connect bias inside of each channel together. Also bias for channels separated.

I'm sorry, that PSU schematic for 1xGU50 per channel.

For 2 tubes in parallel needs (22 k pot + 10 k resistor + capacitors) for separate trim bias each tube in channel.

[costis_n]

I have great respect for Russian DIY, but I see some issues with this schematic.

- Max G2 Voltage for GU60 is 250 V
- No grid stoppers anywhere, and especially no G2 stopper in the GU50's
- Surely is 6e5Π enough to drive 2X GU50 grid capacitance in triode?

[artosalo]

Max G2 Voltage for GU60 is 250 V

In triode connection 400 V is allowed (according to original LS50 specs.)

Surely is 6e5Π enough to drive 2X GU50 grid capacitance in triode?

Why not ?
µ of GU50 in triode mode is only some 5,5, so the Miller-capacitance is quite low. The output impedance of 6e5p seems to be about 10 kilo ohms only. No problem.

[quikie22]

Agree with arto. Have built another amp with 6e5p and gu-50. It gives a very clean and detailed sound. Mine is cathode bias instead of fixed bias. But I run both in pentode mode but with local feed back.

[costis_n]

Originally Posted by quikie22

Agree with arto. Have built another amp with 6e5p and gu-50. It gives a very clean and detailed sound. Mine is cathode bias instead of fixed bias. But I run both in pentode mode but with local feed back.

My question was about triode mode, where there are the limitations I asked about.

[quikie22]

Dunno why my post came out twice. Typing off a smartphone seems to give a variety of problems.

Anyway I tried with 6e5p driver into gu50'triode too. It works very well and sounded excellent on my foster high-eff horns. Unfortunately I needed extra power to feed my 89db kef speakers hence the switch to pentode.