Tremolo issue - AB763 amp

[überfuzz]

The tremolo doesn't fire properly.

The tremolo works fine when it's on, but it doesn't fire properly. First when the amp is turned on and cold the tremolo is hard to get going. Then after some minutes it works, or fires, when the foot switch is pushed.

Id like some pointers on this... If I've understand this correctly the negative bias voltage is killing the oscillation hence stopping the tremolo. Does the bias voltage alter when the amps is getting into proper temperatures? I'm puzzled, what should I be looking for, trying to fix this..?

[txstrat]

Have you considered a cold or broken solder joint around the tremolo circuit, which makes contact only when the amp has warmed up?

[überfuzz]

Well, I've consider checking the solder joints, but I didn't know that a bad one could behave like that. Thanks!

[Enzo]

Never think up reasons not to check something, yes solder joints can act that way. SOlder and resistor leads are all metal and are going to expand and contract with temperature. PLus parts can do that internally.

If this is a real AB763 rather than something you built, there are old parts in there. The three feedback caps in the oscillator are suspect, as are the cathode bypass caps there. And did you try more than one trem tube?

[JHow]

I had cold solder joints (came that way from factory) on the wiper motor controller on my 1997 Chevy S-10 pickup. During warm weather (no rain) the wipers worked fine, during rain (cold weather) the joints contracted and the wiper failed to operate. Basically the wipers worked when I didn't need them and failed when I did. Eventually I read about the problem on the internet, re-soldered the board and that fixed it.

[überfuzz]

Enzo - LOL How could I do that when I didn't even know about this issue.

JHow - It's alive and it has a soul, right!?

[JHow]

JHow - It's alive and it has a soul, right!?

I knew it was an inanimate object, but it behaved spitefuly, like it had a mind of its own.

[überfuzz]

Well ,you really know how much you loved it when you part from it. I had a bass which I sold some 10 years ago. I still miss it.