A DVM on AC could show the effectiveness and balance of the power supply elyticaps for starters. If the amp is passing a signal, but with him, check for hum with the level controls fully down to find whether fault is internal or external to the amp.
the top orange one is just a bent right hand lead. it is connected very well.Third pic down then..have a look..cap on the lower left...looks like a resister....lead on the right hand side...
A DVM, Oscilloscope, and in-circuit ESR checker are handy for basic checks, many hobbyists might have only a DVM.
The o'scope can show you if the power supply is sufficiency "clean", and the residual hum and noise level.i have a dvm. i'm used to working on tube guitar amps so this is a different animal to me. i did just recently buy a used heathkit oscope but i have not done any beginners practicing. i believe it is a 40ms scope and i have a 10x probe.
i hope to do my testing tomorrow. i've built a load box with 4 and 8 ohm resistors and cheapo 6" speakers when i need to hear something.
thanks,
Have you called AudioClassics?i broke down one of my two mc250 amps due to a hum. i have not run any voltages yet. i'm enclosing some pics. though old, 1967, the can caps and axials all seem fine. i don't see any burn spots anywhere.
any recommendations?
thanks,
mikeB
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DC imbalance as well, check both.yep, agree with Pio1980, you need to measure the power supply caps. If you don't have an ESR meter,. you can use a DVM set to AC mv and look for AC ripple on the meter. Anything over a few mv would suggest the caps are shot.
can you elaborate on what you mean by a DC imbalance - between positive and negative rails with reference to ground? As I bring mine up on variac the offsets are not the same even if I switch the 9300uF cans.DC imbalance as well, check both.
DC and AC voltages should be essentially identical between them, a balanced condition.can you elaborate on what you mean by a DC imbalance - between positive and negative rails with reference to ground? As I bring mine up on variac the offsets are not the same even if I switch the 9300uF cans.