now here is an interesting tremelo problem

pula58 · Post by **pula58** » Sun Mar 23, 2014 9:18 pm

Guy brings-in his silverface Deluxe reverb. Reports that the tremelo stops and starts while switched-on. I listen and hear what he's talking about.

So, I take the chassis out and put in on the bench and test the crap out of it and it works perfectly. So....I put the chassis back in the cab, and the trouble re-appears.

So I think, maybe the metal (shielding) screen on the roof of the cab is causing the oscillator stop/start due to the capacitance between part of the oscillator and ground (the shield is at ground since it contacts the amplifier chassis).

So, I lay a piece of flat aluminum (a blank amp chassis) on top of the fender chassis and connect the blank chassis to ground (so it acts just like the screen in the fender cab...and the oscillator behaves normally.

I am at a loss on this one...for now!

Phil_S · Post by **Phil_S** » Sun Mar 23, 2014 9:32 pm

Something to do with the chassis bolts flexing the chassis? It could be ever so little, but enough to trigger something.

pula58 · Post by **pula58** » Sun Mar 23, 2014 10:58 pm

Phil_S wrote:Something to do with the chassis bolts flexing the chassis? It could be ever so little, but enough to trigger something.

update: If I cover the top of the chassis with a cardboard sheet, the tremelo stops.

pula58 · Post by **pula58** » Sun Mar 23, 2014 11:54 pm

it was a bad tremelo "bug"....All I can figure is that the bug resistance was too high and light needed to be on it to get its resistance low enough to work. In other words, the 2nd half of the 12ax7 that drives the bug couldn't drive it hard enough without some assistance from ambient light. At least, that's my theory!

Stevem · Post by **Stevem** » Mon Mar 24, 2014 11:05 am

yea, I`ve had that same thing with a bug doing that, but first I had to remember that the reverb foot switch RCAs got to be plugged in also, not just the trem RCA.
If I am overhualing a whole amp for someone and they use the Trem, I just replace the bug during the process anyway.

Cliff Schecht · Post by **Cliff Schecht** » Mon Mar 24, 2014 4:36 pm

I had an issue last night where a real 5C2 Princeton was self-oscillating but not like a loud screeching noise, it was literally like I set the depth on max and speed on minimum on tweed amp with trem! Never had that one happen before, but it was also very evident that the two signal caps were dead.

The Amp Garage

now here is an interesting tremelo problem

now here is an interesting tremelo problem

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