Jeff Haddad
Senior Member
It's a little slow around here, so I thought I'd put this up for comment.
A couple weeks ago I pulled my modded (not by me) Bandmaster out from the back of the closet after not playing it for a few years. It's an early silverface (chassis stamp 51st week of '67) installed in a 3x10 combo cab and "brownfaced" cosmetically. It must have been recapped when the mods were done. The filters and board e'lytics are newer. It's got a Mercury Magnetics Bassman 2 ohm OT. I didn't check yet, but the PT must be different since it runs a tube rectifier. That and bias tremolo appear to be the mods. Brought it up slowly with a variac - as it heated up, it got noisy. Sporadic roar/white noise/etc. It seemed to have a couple microphonic preamp tubes so I started with the PI and replaced it with an NOS Amperex 12AT7 I got a couple months ago. A little better, but still the noise as it heats up. I swapped in all new preamp tubes and that wasn't the problem.
I put it away for a week and tried again this past weekend. I swapped in new 6L6's, checked the bias and still had the noise. Put the old ones back in and checked the controls on both channels. The noise would even happen with nothing plugged in and both channel volumes all the way off. Then I noticed that as I moved the normal channel volume knob, I could affect the noise - kind of make it come and go. I pulled the chassis and looked around and found that a cathode resistor on the normal channel looked charred so I replaced it. Bingo! I can now play this amp, and it sounds great. For an amp hack like me, that's a feeling of accomplishment.
It's a cool-sounding tremolo, and the amp likes pedals 'cuz its base sound stays pretty clean. Here's a pic:
A couple weeks ago I pulled my modded (not by me) Bandmaster out from the back of the closet after not playing it for a few years. It's an early silverface (chassis stamp 51st week of '67) installed in a 3x10 combo cab and "brownfaced" cosmetically. It must have been recapped when the mods were done. The filters and board e'lytics are newer. It's got a Mercury Magnetics Bassman 2 ohm OT. I didn't check yet, but the PT must be different since it runs a tube rectifier. That and bias tremolo appear to be the mods. Brought it up slowly with a variac - as it heated up, it got noisy. Sporadic roar/white noise/etc. It seemed to have a couple microphonic preamp tubes so I started with the PI and replaced it with an NOS Amperex 12AT7 I got a couple months ago. A little better, but still the noise as it heats up. I swapped in all new preamp tubes and that wasn't the problem.
I put it away for a week and tried again this past weekend. I swapped in new 6L6's, checked the bias and still had the noise. Put the old ones back in and checked the controls on both channels. The noise would even happen with nothing plugged in and both channel volumes all the way off. Then I noticed that as I moved the normal channel volume knob, I could affect the noise - kind of make it come and go. I pulled the chassis and looked around and found that a cathode resistor on the normal channel looked charred so I replaced it. Bingo! I can now play this amp, and it sounds great. For an amp hack like me, that's a feeling of accomplishment.
It's a cool-sounding tremolo, and the amp likes pedals 'cuz its base sound stays pretty clean. Here's a pic:
