scott17,
I look forward to your schematic, if and when you find the time.
In my Post # 299, I looked at the schematic in Post # 290.
It was the last schematic posted, and when someone after a posted schematic talks about their amplifier but does not say which schematic, I automatically assume the last one to be what their amplifier is like. That is often the wrong assumption.
You said you changed from triode mode to UL mode. That is easy for me to look at another schematic, and make the change of the screen connection in my mind.
You also said that you had a 133kHz oscillation.
My post 299, section B. 3. was to answer your questions.
Even though it was only in one channel, and swapping the output tubes did not fix the oscillation; and the output transformers should be fairly identical, the right channel could be just beyond good stability, and the left channel just inside of good stability.
Perhaps the wiring dress is different for the right channel, than the left channel.
It would be nice if we are able to figure out the cause of your 130kHz oscillation, even though you seem to have a fix for it.
I always use a non-inductive 8 Ohm load resistor for testing my amplifiers.
Just because one of my amplifiers is stable on that load, with a loudspeaker if may not be stable.
So after testing with the load resistor, I test with one or more loudspeakers.
Different loudspeakers have different impedance versus frequency.
I put an impulse through the amp and test the broadband spectrum; If that looks good, then I load the CD player and listen to music (with the scope / spectrum analyzer still monitoring the amplifier.
The other parts of my post were for other posters, based on what they said (of course you might find those additional answers I gave useful too).
In earlier posts there were comments about the feedback, and about the cathode bypass cap.
My post 299, sections A., 1. 2. were to give my thoughts on those earlier comments.
NickCool2000 mentioned hum and buzz. My post 299, sections B. 1. and B. 2 were to address that.
My post 299 section 4. was to warn newbies that the secondary must be grounded. The schematic in post 290, sort of hid the ground symbol there, easy to overlook, I did too.
I look forward to your schematic, if and when you find the time.
In my Post # 299, I looked at the schematic in Post # 290.
It was the last schematic posted, and when someone after a posted schematic talks about their amplifier but does not say which schematic, I automatically assume the last one to be what their amplifier is like. That is often the wrong assumption.
You said you changed from triode mode to UL mode. That is easy for me to look at another schematic, and make the change of the screen connection in my mind.
You also said that you had a 133kHz oscillation.
My post 299, section B. 3. was to answer your questions.
Even though it was only in one channel, and swapping the output tubes did not fix the oscillation; and the output transformers should be fairly identical, the right channel could be just beyond good stability, and the left channel just inside of good stability.
Perhaps the wiring dress is different for the right channel, than the left channel.
It would be nice if we are able to figure out the cause of your 130kHz oscillation, even though you seem to have a fix for it.
I always use a non-inductive 8 Ohm load resistor for testing my amplifiers.
Just because one of my amplifiers is stable on that load, with a loudspeaker if may not be stable.
So after testing with the load resistor, I test with one or more loudspeakers.
Different loudspeakers have different impedance versus frequency.
I put an impulse through the amp and test the broadband spectrum; If that looks good, then I load the CD player and listen to music (with the scope / spectrum analyzer still monitoring the amplifier.
The other parts of my post were for other posters, based on what they said (of course you might find those additional answers I gave useful too).
In earlier posts there were comments about the feedback, and about the cathode bypass cap.
My post 299, sections A., 1. 2. were to give my thoughts on those earlier comments.
NickCool2000 mentioned hum and buzz. My post 299, sections B. 1. and B. 2 were to address that.
My post 299 section 4. was to warn newbies that the secondary must be grounded. The schematic in post 290, sort of hid the ground symbol there, easy to overlook, I did too.
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