03-02-2018, 10:57 PM
So I experimented with those cap values this evening. Installing 0.1uf's improved the red plating problem significantly but did not resolve it. I jumped to 0.015uf's and the red plating was non existent. I then swapped in 0.022's with still, no issue. So it seems as if that solved the problem. The amp still sounds great but I'm just wondering how much of those "Ampeg Lows" I actually cut.
Monday I plan to experiment with a few more cap values, working as close to the original 0.33uf mark as I can before these JJ 7027's start to red plate again. When I settle on a value that works I'm going to attempt to do a spectral analysis to see how much low end I have lost as compared to what the circuit does with the original 0.33uf values. I'll be sure to post my results and upload some traces if I can.
I'm curious if it is normal to see a blue haloing effect in a pair of tubes on V4's while playing. It seems as if my "problem" pair of tubes glows blue as I dig into a chord, while the other pair does not exhibit this glow until the amp is idle.
AMPREPAIRJN, thanks for spending so much time on this thread, I really appreciate it! Aside from NOS 7027A's, what do you recommend as output valves for these amps?
Monday I plan to experiment with a few more cap values, working as close to the original 0.33uf mark as I can before these JJ 7027's start to red plate again. When I settle on a value that works I'm going to attempt to do a spectral analysis to see how much low end I have lost as compared to what the circuit does with the original 0.33uf values. I'll be sure to post my results and upload some traces if I can.
I'm curious if it is normal to see a blue haloing effect in a pair of tubes on V4's while playing. It seems as if my "problem" pair of tubes glows blue as I dig into a chord, while the other pair does not exhibit this glow until the amp is idle.
AMPREPAIRJN, thanks for spending so much time on this thread, I really appreciate it! Aside from NOS 7027A's, what do you recommend as output valves for these amps?