OK. I unsoldered both C11s.
Update regarding the feedback:
It seems the feedback is not the problem.
Now i get those popping noises even with original feedback settings.
If the volume exceeds a certain level there is this popping sound at one channel. I tried swapping all the tubes, drivers and output tubes, as i read it may be arcing but the problem is still here.
Next thing i did is solder all the anode resistors of the driver tubes again - popping still occurs. I also measured the values of the resistors - they seem OK...
There are so many new problems since i swapped the output tubes, that cracks me up 🙁
Update regarding the feedback:
It seems the feedback is not the problem.
Now i get those popping noises even with original feedback settings.
If the volume exceeds a certain level there is this popping sound at one channel. I tried swapping all the tubes, drivers and output tubes, as i read it may be arcing but the problem is still here.
Next thing i did is solder all the anode resistors of the driver tubes again - popping still occurs. I also measured the values of the resistors - they seem OK...
There are so many new problems since i swapped the output tubes, that cracks me up 🙁
Original feedback setting may be completely unsuitable with your modified circuit.
I have earlier told you how to re-adjust the GNFB components. Have you done this ?
Arching of the tube happens VERY seldom. I have not experienced such during last 45 years with my tube gears.
I also suggested you to check the operation with 6J32P removed and signal fed directly to 6N6P. Have you done this yet ?
I tried to run the amp without feedback again. First there was a low frequency square wave shown on the scope... Then i swapped the ground and the tip of the scope on the 8Ohm resistor - then there was the sine wave...
No idea why.
It took very low input voltage to get 10V output. Then i placed the 50k pot and adjusted the output voltage to 2V. -> 32,9k Ohm
Found a 33k resistor and used it.
Tomorrow i will give it another try.
No idea why.
It took very low input voltage to get 10V output. Then i placed the 50k pot and adjusted the output voltage to 2V. -> 32,9k Ohm
Found a 33k resistor and used it.
Tomorrow i will give it another try.
Seems that the input signal was far too high. How much was it ?
Where was it connected at first ?
Is this the NFB-resistor ? If it is, the GNFB is now 14 dB, which is a good value to proceed with.
Good to know!
I did not change it. When i swapped the probe connections it worked.
Ground clip on 8 Ohm output and tip on the minus output.
I think that caused problems...
It was acting normal with ground clip on minus output and tip on 8 Ohm output.
Yes - i adjusted it like you told me.
As editing is unnecessary complicated in this forum - another double post...
Just did another test with the new feedback setting.
There is really loud hum now.
The popping noise is still there.
As the other channel works well with the original feedback settings without popping etc. it has to be a faulty component like a resistor...?
Just did another test with the new feedback setting.
There is really loud hum now.
The popping noise is still there.
As the other channel works well with the original feedback settings without popping etc. it has to be a faulty component like a resistor...?
For sure that caused problems. You made a short circuit at the output.
"Minus" output connector is ground and "plus" output is the signal connector.
You may NOT connect the minus clip of the oscilloscope to any other point than GND.
Third time: check the operation with 6J32P removed and signal fed directly to 6N6P.
Can you tell me what the primary inductance of the original Priboi output transformer is ?
Do you use original cores or what ?
Ok i will do that.
When i remove the 6J32P i would also remove C6 and feed the signal with another capacitor directly on the grid. Is that OK?
My cheap RLC Meter says 0,31H measured at the power plug.
Thank you very much for your patience, artosalo
Do not remove C6. Just feed the signal directly to the grid of 6N6P.
The required signal level is now essentially higher because the gain of 6J32P is not included.
The required signal level is now essentially higher because the gain of 6J32P is not included.
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I soldered the input signal cable directly across R8.
It works. Like you said the gain is lower.
The sound is distorted and there is hum again. When i increased the input volume to max there was no popping noise.
I think it was well above the volume were the popping normally occurs!
What could i try next?
It works. Like you said the gain is lower.
The sound is distorted and there is hum again. When i increased the input volume to max there was no popping noise.
I think it was well above the volume were the popping normally occurs!
What could i try next?
How ? Symmetrically ? What power level you reach at the clipping level?
Connect the grid of 6N6P direcly to ground near tube socket.
What happens to hum level ?
I just listened to music...
The sound is distorted, the mids are missing, the high frequencies sound terrible.
When i read your post i hooked it up to the scope and the function generator and tested it. It is not perfectly symmetrical and it was clipping at the same level. But i needed nearly 6V input to get it to clipping level.
When i short R8 the hum decreases a little bit.
To make sure:
When both 6J32P are removed, the one channel is silent and works OK.
The other has distorted sound and hum.
Correct ?
When both 6J32P are removed, the one channel is silent and works OK.
The other has distorted sound and hum.
Correct ?
No i just converted the channel that makes the popping noises.
I would say the distortion is present because of the missing feedback.
With the 6J32P in place the sound is OK but the popping noise appears at a certain volume. So the problem must be somewhere at the 6J32P i guess...
Maybe the anode resistor?
I did accidently found this thread and got very interested as I have a Priboi lurking under my bed. Now that you are discussing a special rebuild, using specific tubes.
I do not want to mess around too much but just throw in a, sort of quickie.
I did a total rebuild according to Likhnitsky's schematics in Russian Audio Magazine back in the 90's and wwas happy with that, but I know the amp has a much larger capacity that the 10-12W I have available and have ideas of using more reliable tubes than the 6R3S.
Mr Liknitsky made, he stated, once a successful trial with EL34/6CA7. I on the other hand do not want to purchase new/more tubes but have some in my boxes to try out: 6L6, CV1075, GU50 and 6S36P/EL500.
What would be a first choice between these tubes?
I do not want to mess around too much but just throw in a, sort of quickie.
I did a total rebuild according to Likhnitsky's schematics in Russian Audio Magazine back in the 90's and wwas happy with that, but I know the amp has a much larger capacity that the 10-12W I have available and have ideas of using more reliable tubes than the 6R3S.
Mr Liknitsky made, he stated, once a successful trial with EL34/6CA7. I on the other hand do not want to purchase new/more tubes but have some in my boxes to try out: 6L6, CV1075, GU50 and 6S36P/EL500.
What would be a first choice between these tubes?
The output transformer of Priboi is 2k7 ohms to 8/4 ohms.
This feature is very unsuitable for typical tubes like EL34, 6L6 GU50 etc.
The reason for low impedance level is that the original configuration is actually parallel push pull. Therefore the best type of tube is such that has high gm, like PL519 and its relatives.
From the tube list you made I would pick up 6P36S, but the supply voltage of original Priboi is bit too high to be optimal for this.
If EL34 or 6L6 would be used, the optimum operation was achieved with 4 tubes / channel.
This feature is very unsuitable for typical tubes like EL34, 6L6 GU50 etc.
The reason for low impedance level is that the original configuration is actually parallel push pull. Therefore the best type of tube is such that has high gm, like PL519 and its relatives.
From the tube list you made I would pick up 6P36S, but the supply voltage of original Priboi is bit too high to be optimal for this.
If EL34 or 6L6 would be used, the optimum operation was achieved with 4 tubes / channel.
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