Many thanks for the revised circuit. Just to double check before I start work, that gives me:-
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the same for me
6p3s-e
ecc85
6n2p-ev
330ohm bias resistor .
I think modify the chassis to gain a little height to add a choke.
by that, I love it.
6n1P-ev not 6n2P-ev ...
Just a quick question. Instead of adding a voltage doubler, would changing the values of the resistors marked in red have a similar effect?
An externally hosted image should be here but it was not working when we last tested it.
I greatly appreciate all the many contributions above which considered but have lived with the stock standard amp for 10 years now, albeit for occasional use. For me, the overriding visceral pleasure of a tube amp for me excuses the several shortcomings of this example.
However, the amp has developed an issue with the right channel emitting an unpleasant grating noise. I have therefore been working through find the cause. Left channel appears fine, having swapped over all the tubes left to right and back again. Internally, there are no obvious visible issues and I have measured and compared voltages right vs. left. These are mirrored give or take, although right tends to be very slightly less. I am not ruling this out as a symptom but it doesn't point to anything obvious. I am confident that all the tubes are functional. I have not found any resistor issues so my best guess at the moment is one of the capacitors. There is not much else and which would be consistent with the pop which coincided with the onset of the issue. I plan to proceed with testing/replacing and whilst I am at it go the extra step of uprating the specs, according to the recomendations posted above.
Anyway, my issues aside whilst troubleshooting I did notice something that has possible been missed and that is a error in the circuit diagram (or possible the revision of my amp).
I don't recall seeing this called out anywhere and, interesting to know if this has been encountered otherwise, especially as this also affects the voltage doubler in the previous, most 'recent' post. I found that the 30K resistor in proximity to the 6e2 is not connected between ground <> 8ohm output terminal but between ground <> diode cathode. Images attached.
However, the amp has developed an issue with the right channel emitting an unpleasant grating noise. I have therefore been working through find the cause. Left channel appears fine, having swapped over all the tubes left to right and back again. Internally, there are no obvious visible issues and I have measured and compared voltages right vs. left. These are mirrored give or take, although right tends to be very slightly less. I am not ruling this out as a symptom but it doesn't point to anything obvious. I am confident that all the tubes are functional. I have not found any resistor issues so my best guess at the moment is one of the capacitors. There is not much else and which would be consistent with the pop which coincided with the onset of the issue. I plan to proceed with testing/replacing and whilst I am at it go the extra step of uprating the specs, according to the recomendations posted above.
Anyway, my issues aside whilst troubleshooting I did notice something that has possible been missed and that is a error in the circuit diagram (or possible the revision of my amp).
I don't recall seeing this called out anywhere and, interesting to know if this has been encountered otherwise, especially as this also affects the voltage doubler in the previous, most 'recent' post. I found that the 30K resistor in proximity to the 6e2 is not connected between ground <> 8ohm output terminal but between ground <> diode cathode. Images attached.
An externally hosted image should be here but it was not working when we last tested it.
6J6 has a 7 pin base, so not directly compatible. Lots of 6N1P variants to roll if you choose.
KT66 draws more heater current, which maybe too much for the power trans. Russian 6P3S-E is an excellent tube.
jeff
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I just noticed your amp comes stock with 6L6GC, and is cathode biased. I'd be careful trying smaller 6L6 equivalent tubes, as they may "red-plate" in your amp. You need to check voltages and plate dissipation first.
jeff
If you want more bass then turn up the bass control. --Oh you don't have one ? Then replace the amp or speakers.
Tubes are indifferent of frequencys in the audible range. Any differences comes from the circuit and the Ri differences of the tube.
Hi, I recently bought a Yaqin MC-5881A amp, I checked the power tubes bias voltage, it is 34 volt, it looks like the idle
current is too high, the filament voltage is a little bit high also.
I had doing some modification.
Removed one of the cathode 500r resister, I check the cathode voltage is 40 volt, the idle current is reduce from 68 ma to 40 ma. But I found two issued, the maximum output is drop from 21w to 15w and has crossover distortion at high output. I solved these issued by add a transistor to make the cathode bias to
a dynamic bias, after this changed the maximum output is up to 21w and no crossover distortion.
Add a thermistor to the ac input line.
Removed the 30K resister to increase the sensitivity of the level tube.
current is too high, the filament voltage is a little bit high also.
I had doing some modification.
Removed one of the cathode 500r resister, I check the cathode voltage is 40 volt, the idle current is reduce from 68 ma to 40 ma. But I found two issued, the maximum output is drop from 21w to 15w and has crossover distortion at high output. I solved these issued by add a transistor to make the cathode bias to
a dynamic bias, after this changed the maximum output is up to 21w and no crossover distortion.
Add a thermistor to the ac input line.
Removed the 30K resister to increase the sensitivity of the level tube.
