Tremolo Issue

[gbono]

I'm working on a Acoustic model 150 amplifier which appears to have been built in 72-73'. The tremolo on this amplifier does not use the opto device but it has a discrete (JFET/bipolar) design.

The tremolo works okay for about 5 min then it cuts out. Adjusted the trimmer pot and have "shot-gunned" some of the critical components but the problem still exists. I was hoping someone was familar with this circuit and could point me in the right direction? THX

[Rob Mercure]

Until someone more familiar with this amp such as Enzo replies I'd suggest looking at solder joints and electrolytic caps. Solder joints heat up expand and break contact. Electrolytic caps fail with age and heat and if old and leaky produce their own heat.

Rob

[52 Bill]

When the tremolo stops, does the oscillator still run and there is no effect, or does the oscillator die out?

If you look at what is happening to the circuit when the symptoms start, you will know where to start looking for the problem.

[Enzo]

Bill is on it, I don't know the 150 off the top of my head.

But does the trem stop like a switch was thrown or does it peter out over a second or two or does it come and go?

Every trem has an oscillator and an interface. If the trem stops, it is either the oscillator stopping or the interface failing. The osc will be based on a tube, a transistor, an op amp, something with gain. At the output pin of whatever type it is, ther is either hte low frequency signal or there is not.

The interface can be an optocoupler, an LDR, or even just a cap, but it must transfer the low freq osc signal to the rest of the amp.

Find out just what is the nature of the trem failure and it should be easy enough to track down.