Randell amp

I'm working on a Randell amp...I changed the 2 electrolitic caps in the
power supply..but it still has a hum when the volume is turned up
alittle...I esr'ed the other caps in circuit and they look ok......help
....... any suggestions ? thanks

 

Are you able to point to a schematic? I am thinking hum-loop, dirty
controls or a leaking bypass cap. As to the two electrolytics you did
replace, make sure that you followed the schematic exactly. In some
cases these caps are part of a voltage-doubler circuit, so (at least)
one will be above ground on both ends. Similarly for an LC circuit.

Peter Wieck
Wyncote, PA

 

Peter...thanks for your answer....I got this unit to repair and
whoever ...... replaced the 2 large caps in the pwr supply... but
they had them reversed....and it kept kicking the breaker out...I
rewired them and it don't kick the breaker now but the hum is
there..I checked the caps with an ESR meter and they look ok...but I
wonder if wiring them backwards ruined the caps....what other test can I
do on them.....thanks

 

It is quite likely that the caps are ruined. In any case, I would not
trust them given the (relatively) low cost of replacements. Additional
tests that I perform even on new caps right out of the box/bag is a
full-voltage test on a cap checker, as well as a simple confirmation
of basic capacitance.

Good luck with it.

Peter Wieck
Wyncote, PA