Thanks for your info W5JAG.
Specifically the issue I have may have started from day one when I built the SSE 4 years ago. I’ve always had a volume difference between the left and right channels, left channel always dominant. I checked and rechecked every component and both sides compare equally within the component tolerance. Back then both channels sounded very good, just one side louder than the other, so since every else seemed OK I installed a dual concentric volume control so I could balance left and right as needed. At lower volume both were the same, as it went higher the difference grew. It worked well for 4 years. Now the weak right side has developed distortion, severe to the point where I have to use 1K bias resistors for R17/R27 to get good sound with cheap Chinese 6L6GC’s. I can’t even use my newer Tung-Sol 6550’s anymore at any cathode bias without distortion, which use to sound great. Also over the years it seems some of my tubes have gone bad. I’ve gone through 2 or 3 12AT7’s and 2 5AR4’s. Bad luck? I don’t know, but they were NOS, not the new stuff.
So I started taking voltage reading and found a somewhat discrepancy between the right and left channel (right being higher) and thought maybe that could point to what the problem could be.
My initial thought was that the right side CCS has a 1V difference between input and output and the left has 12V difference, which seemed odd. However in the end both output tubes do have the same 386V on the plate, so… I don’t know.
I’m seeing the same voltage differences regardless of what input source or 12AT7 tube or output tube I use. Maybe the right CCS bad? But it seems like I'm running more tha 10ma on both CCS's at the 330 ohm resistor. But only the right channel sounds distorted.
Right channel CCS:
P 330V, G 325V, A 329V, 12at7 PLATE 326v
Left channel CCS:
P 330V, G 310V, A 317V, 12at7 PLATE 313v
Additional info:
All components except motor run caps and iron are from Mouser and Digikey
PT: Allied 6K7VG
C1: 35mf 440V motor run cap
Triad C-14X choke
C2: 100 mf electrolytic 500V + 50mf 350V motor run cap
B+: mostly 415 (my line voltage is 115V-117V)
OPT: Transcendar TT-212-OT (older, like 312)
C11/C21 Mundorf Supreme .22 1200V
Power Tube: NOS Sylvania & JAN 5AR4 (several)
Driver tube: 12AT7: NOS Sylvania, NOS RCA, JAN
Output tubes: Can’t blow up Chinese 6L6GC, =C= 6L6GC (still seems Ok @ 1K), Tung-Sol 6550 Seems dead now at any cathode bias.
I use Triod mode only
Have not drilled out any pads on the PC board to inset components
5 selector cathode bias switch: 1K on board, 750, 630, 560 and 470 – only 1K is useable now!
25K dual concentric volume control
Thanks for any help anyone can give me,
Mike