I fired this amp up for the first time in a long time after a friend replaced the 6CA4 rec tube. Here is a video of the problem.
I just cleaned the pot and nothing changed. I assume it’s not the best pot but not sure it’s the issue.
Sounds like some serious RF there. ;-) What source is plugged into it? Does it do that with the inputs shorted? Have you tried a different input tube? Is the amp near or on top of any other equipment or a TV?
I plugged it into my iPhone then my Fire tablet then nothing at all. Same issue with all of them. I ripped the surround on my test speakers and waiting for it to dry before I go further.
My plan is to short the inputs, cover it with a steel bucket, and see if I can find a 6EU7 input tube here locally to swap.
My plan is to short the inputs, cover it with a steel bucket, and see if I can find a 6EU7 input tube here locally to swap.
I shorted the inputs and 90% of the noise disappeared. I pulled all the tubes and swapped the output tones and that got rid of 5% more, then it came down to wiggling the positive wire on the right speaker and now no noise.
Weird stuff. I’m listening to Caravan from the movie Whiplash and it rocks!!!!
Thanks everyone.
Weird stuff. I’m listening to Caravan from the movie Whiplash and it rocks!!!!
Thanks everyone.
That sound is called "squeeging" and is the result of a very high frequency instability being interrupted at an audible rate, as the amplifier goes in and out of oscillation rapidly. The solution is to stop the VHF oscillation. Grid stops, check the grounds, output terminal Zobels, round up the usual suspects.
All good fortune,
Chris
All good fortune,
Chris