i am not sure. ITs a black poweramp, with a horrible yellow 'neon' switch. a21a. Looks latte 80's. I checked the caps, they all seem fine (nothing dry etc). time to looks at joints. the sound distorts pre cutting out. could this potentially be bad output trannies, i know sugden bias the hell out of them.
adamus said:i am not sure. ITs a black poweramp, with a horrible yellow 'neon' switch. a21a. Looks latte 80's. I checked the caps, they all seem fine (nothing dry etc). time to looks at joints. the sound distorts pre cutting out. could this potentially be bad output trannies, i know sugden bias the hell out of them.
Probably right at the front end.
If it was in the power section, something would have blown !!
Sounds like one of the supply rails in dropping out.
Andy
Do you have a meter etc. You are going to have to take some measurements, possible comparing left/right. The output midpoint is as good a place as any to measure first as any power amp problem will probably show up here first.
Does it seem heat related, going duff after say 30 mins from cold.
Is the speaker output AC coupled on this one --- single rail supply.
When it goes faulty is it "tapable" if you poke the PCB with it on.
When it goes faulty does it stay that way until you switch off.
Does it seem heat related, going duff after say 30 mins from cold.
Is the speaker output AC coupled on this one --- single rail supply.
When it goes faulty is it "tapable" if you poke the PCB with it on.
When it goes faulty does it stay that way until you switch off.
Mooly said:Amazing what a good whack will fix.
I had a similar problem on a new build.
The amp would power up but the output would then very slowly go to B- ! The amp sounded fine with music through it to start with.
Turned out to be a dry solder joint on an input resistor that tied the input to ground.
A21a single ended class A
Had this one sitting for a while waiting its turn... one channel was dropping out. Turned out to be a faulty bridge rectifier B80 C3200/2200; replaced it with B500 C7000/4000. Tricky / intermittent. The amp appears to be soldered & put together in a back-shed. Unbelievable...
Anyway, if there's a drop-out -> check bridge rectifiers as well.
Nick
Had this one sitting for a while waiting its turn... one channel was dropping out. Turned out to be a faulty bridge rectifier B80 C3200/2200; replaced it with B500 C7000/4000. Tricky / intermittent. The amp appears to be soldered & put together in a back-shed. Unbelievable...
Anyway, if there's a drop-out -> check bridge rectifiers as well.
Nick
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