Hi all,
So I finished my trinity tweed complete with VRM a couple of weeks ago and it has worked and sounded excellent at all volumes and VRM levels... until a few days ago.
Here's a sequence of events and symptoms:
-Noticed that rectifier tube arced when I turned the amp on a couple weeks ago. It maybe happened again once or twice in the past few weeks but everything seemed to work fine.
-A few days ago I turned on the amp, heard no sound, checked guitar cables and volume knobs, all plugged in and turned up, strike the strings and hear a pop, and then it came to life and sounded as glorious as usual. Hmm, that was weird.
-Next day, same thing. Hmm, that was weird again, but it's still working. Perhaps a loose connection I thought.
-On the third day, no sound at all. It was then that I noticed when I strummed or struck the strings of the guitar, tubes V3 and V4 had a blue glow that seemed to dance with my strumming. Now, I've read that a blue glow is normal. Perhaps it was always there and I hadn't ever noticed it before, or perhaps not.
Here's how I've troubleshooted so far:
-Used ohmmeter to check for bad solder connections on all pins of V3 and V4, output jacks, speaker cable, and speaker cabinet. All measured zero or next to zero resistance, so no problems there.
-Checked the ohms of resistors R7,8,13,14,16,17,18,19,20,21,and 22. All were good.
-Used a wooden dowel to poke and wiggle some wires with the amp on, to no effect.
-Gave the amp a few gentle bumps and taps to see if a shoddy connection would respond. No effect.
-Measured voltages as follows: (JJ tubes, except V1 is electroharmonix) -AC Mains: 120 VAC -B+ all tubes in: 380 V -V1 -Pin 1: 112 V -Pin 3: 1.97 V -Pin 6: 109 V -Pin 8: 1.97 V -V2 -Pin 1: 148 V -Pin 3: 1.18 V -Pin 6: 188 V -Pin 7: 2.7 V (aha! should be 17 V. Also noticed that the V3 & V4 blue glow light show did a dance whenever I touched the lead to Pin 7) -Pin 8: 46 V -V3 -Pin 3: 375 V (a bit high? Manual says it should be 356 V with the JJ rectifier) -Pin 4: 335 V -Pin 8: 21 V -V4 -Pin 3: 380 V (again, a bit high?) -Pin 4: 334 V -Pin 8: 21 V
-Since Pin 7 on V2 was the only one that seemed out of whack, I checked all of the solder connections around it with the ohmmeter, and all were good. I checked R12 and it was fine. (Note, I did not install the optional 470K resistor here.) I touched the leads of the ohmmeter to C6 and then checked the voltage across it and observed it to be slowly draining, which I believe means that it's good.
So, I do not know what to do next at this point. Is it safe to say that Pin 7 on V2 is likely the problem? I triple-checked the voltage on that pin and other locations on the same node, and got the same result every time. 2.7 Volts. Any idea what could lead to a low voltage on that pin? A bad tube perhaps? Does the blue glow in the output tubes that responds to the input signal indicate that the input signal is getting through the preamp to the output stage? If so, could it be a problem with the output transformer?
Any help would be greatly appreciated.
Thanks,
Greg
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