[Amps] Strange Problerm

[Tom Rauch]

> Twice within the past six months we have had amplifiers fail due to
> the loss of all of the power supply filter capacitors in one "bank" of
> the supply.  Both amplifiers (an Alpha 76 and a SB-220) were being run
> on 240 V AC.  In both cases the filter capacitors were "relatively"
> new.  

Whenever capacitors are changed, equalizing resistors should be 
tested. The dividing resistance should be tested AFTER the wiring is 
completed, because it is easy to damage many resistor types.

You can do that by connecting a low-voltage (voltage<500 volt) dc 
supply or low-voltage AC supply to the finished system, and measuring 
drop across each capacitor.

Carbon resistors of ANY type do NOT belong in a voltage equalizing 
system like this. They should be metal film or high reliability wire 
wound resistors. 

 However, a recent comment by an experienced HV power supply builder,
> has brought up the subject of a possible "wild leg" in the 240 V AC
> line to which the amps were attached.  According to this suggestion, a
> large transient VOLTAGE swing on one leg of the 240 V mains put an

Bad answer. He might be a good builder, but regretfully he must not 
fully understand how supplies and power mains work.

You most likely either had defective additional components that you 
missed, or installed bad capacitors. On occasion defective new 
capacitors do show up. 

By the way, I hope you changed all the capacitors with units from the 
same manufacturing batch.73, Tom W8JI
W8JI@contesting.com