AMP QUESTION ? SKIPPER BY PALOMAR AB1

[loosecannon]

hey switch,

could that PCB be doublesided?
if so, and if someone replaced some parts, there is a chance that a component lead on the bottom of the board is either touching, or too close to the metal chassis under it.
maybe try removing the PCB and look underneath for signs of previous repair.
you might even find a cold solder joint or something.

i also agree that unsoldering a couple of leads from the transistors and testing them using the diode function of your multimeter is an easy first test.

freecell, you are one of the smartest people on this forum, but you are by far the least helpful.
yes, this is a technical forum.
it is not a forum for debate, unless the thread was started with that intention.
with all of your knowledge, im sure you can see that switch kit did not start this thread to create a debate.
he started it to get some help.
your primary goal seems to be proving yourself right.
that helps no one.
so, are you here to help people or not?
LC

 

[Switch Kit]

Got a little costly for me but it was just one of those things I had to know . turns out it was not the transistors , it was the mica caps on top of the large transformer , gets tricky , those caps may check out OK on the meter but once power is applied , they can unknowingly change on you.

Very hard for me to explain why ? or why this happened ? but that was the problem , they simply needed to be changed to different values. I'd like to thank all that tried to help me with this one. I now have two good 2879's for a rainy day , my luck , it seldom rains in So.Cal. Thanks

 

[mackmobile43]

Got a little costly for me but it was just one of those things I had to know . turns out it was not the transistors , it was the mica caps on top of the large transformer , gets tricky , those caps may check out OK on the meter but once power is applied , they can unknowingly change on you.

Very hard for me to explain why ? or why this happened ? but that was the problem , they simply needed to be changed to different values. I'd like to thank all that tried to help me with this one. I now have two good 2879's for a rainy day , my luck , it seldom rains in So.Cal. Thanks

I see just by the picture that when this amp is switched to ab biasing then it also switches off any feedback for the output transistors.

 

[kc8adu]

I see just by the picture that when this amp is switched to ab biasing then it also switches off any feedback for the output transistors.

how?
the feedback parts are hardwired.
and i dont see anything on that switch other than a crude step attenuator.
where are the parts for the bias regulation?
on the underside of the board?most likely it does not have any!if not its just marginally better than class c.i suspect it is just a class c amp with a filter for harmonics.