Hot Rod Deluxe problem

[Brad1]

Got the intermittent "bacon sizzle". "pop....kzsht..pop...etc".

Does it with all knobs down. Plugged a guitar into "Amp In', still does it.

Sovtek 5881WXT tubes tested good in tube tester. Replaced with a pair of USA 6L6GC from my BF Bandmaster. Still pops.

Tried the Sovteks in my Bandmaster. No problem. Worked fine.

OK. Hmmm. Took a reading at TP26. Supposed to be 37.2V. This read 29.6V. Tested (good) all 12AX7s. Swapped tubes. Nothing changed.

Is this, perhaps, a cap problem? Which would be most likely, if so? Any other ideas? Any other known issues with these things?

My friend (our other guitar player) has taken this to a local guy, and a guy 30 miles away, paid good money, and issue hasn't been resolved. He said it was good for maybe a week each time, then problem popped back up.

I believe these are all original caps? (Gray "IC" branded, still hot-glued).

BTW, I can't tell what someone did, exactly on another thing.

W4 wire jumper was removed. (Goes to P1A cable left-most wire, which goes to pin 8 of 12AX7, V1B.) R10 (1.5K) was removed, and piggybacked parallel with a 47uF cap, with the bottom (+ end) connected to where the bottom of the W4jumper was (connected to pin 8). Any ideas on that? It's the same brand of cap, but a sloppy job!

Link to Fender schem, in case:

http://www.fender.com/support/amp_sc..._Schematic.pdf

Thanks,

Brad1

[52 Bill]

Got the intermittent "bacon sizzle". "pop....kzsht..pop...etc".

OK. Hmmm. Took a reading at TP26. Supposed to be 37.2V. This read 29.6V. Tested (good) all 12AX7s. Swapped tubes. Nothing changed.

You've correctly figured out that this is a power amp or power supply problem. Before you go too far, check the 82k plate resistor R57, these seem to fail a lot.

Also check the plus and minus 15volt supplies, as there is an op amp at the input to the power amp. Check for voltage on the output pins of the IC as well.

BTW, I can't tell what someone did, exactly on another thing.

W4 wire jumper was removed. (Goes to P1A cable left-most wire, which goes to pin 8 of 12AX7, V1B.) R10 (1.5K) was removed, and piggybacked parallel with a 47uF cap, with the bottom (+ end) connected to where the bottom of the W4jumper was (connected to pin 8). Any ideas on that? It's the same brand of cap, but a sloppy job!

Could be that there was a broken trace on the board and someone moved R10 to go across C56. Or it could be that someone wanted to replace R10, but didn't want to remove the pc board from the chassis and took the cheezy way out.

[Brad1]

Bill,

Thanks for the info. I figured I was getting close. Your suggestion was very close. It wasn't R57, though. It was R58. The 100K resistor was reading over 3M. Replaced that, and sounds good. TP 26 now reads right at 36.9V, which, I guess, is close enough to 37.2V. Bias is set at exactly 60mV.

John will be happy.

Thanks,

Brad