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Old 18th September 2011, 05:33 AM   #1
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Default Help with these Russian GU50 tube amplifier

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.
Однотактный усилитель на ГУ-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
Attached Images
File Type: gif gu50se6e5p.gif (9.4 KB, 1476 views)
File Type: gif gu50sebp.gif (7.2 KB, 1418 views)
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Old 18th September 2011, 08:43 AM   #2
Timofey is offline Timofey  Russian Federation
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>>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.
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Old 18th September 2011, 09:43 AM   #3
Jaap is offline Jaap  Netherlands
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What is the impedance of the OPT ?
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Old 18th September 2011, 10:45 AM   #4
Timofey is offline Timofey  Russian Federation
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3200-3300 Ohm / 8 Ohm
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Old 18th September 2011, 10:55 AM   #5
Timofey is offline Timofey  Russian Federation
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>> >> 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.
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File Type: gif bias_gu50.gif (1.6 KB, 1346 views)

Last edited by Timofey; 18th September 2011 at 11:20 AM.
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Old 18th September 2011, 11:51 AM   #6
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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?
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Old 18th September 2011, 12:52 PM   #7
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Quote:
Max G2 Voltage for GU60 is 250 V
In triode connection 400 V is allowed (according to original LS50 specs.)

Quote:
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.
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Old 18th September 2011, 04:08 PM   #8
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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.
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Old 18th September 2011, 04:12 PM   #9
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Quote:
Originally Posted by quikie22 View Post
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.
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Old 18th September 2011, 04:20 PM   #10
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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.
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