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Cap substitution in Rockola 414 amp rebuild

Posted: Fri Nov 07, 2014 7:48 pm
by cmangeng
In the amp a can type cap has 4 similar taps at 20uf/475v each. I can find no voltages higher than 375v marked on the circuit schematic. I have 22uf/450v caps in my supply. Can anyone familiar with that amp tell me if there would be a problem using the lower voltage caps in this amp? I know you should not go lower with the voltage, but did they just use that cap because that was what was available at the time?
Thanks, Craig.

Re: Cap substitution in Rockola 414 amp rebuild

Posted: Fri Nov 07, 2014 7:58 pm
by MattTech
The measured "initial" peak voltage right off the rectifier upon startup is the key here.
If it stays below 450 volts, I see no reason to worry about using caps with that value.

Re: Cap substitution in Rockola 414 amp rebuild

Posted: Fri Nov 07, 2014 9:28 pm
by cmangeng
MattTech, I'm guessing the listed voltages are not the peak ones, which would require removal of the power distribution assembly to bench test the voltages in the amp? I can do that but was hoping I could use the posted voltages as a guide for what the circuit sees. I missed the center tap voltage at 380v on the output transformer as being the highest voltage shown. It is not a big deal to step up to the 500v cap....its just money. :D
Craig

Re: Cap substitution in Rockola 414 amp rebuild

Posted: Sat Nov 08, 2014 12:06 am
by MattTech
It's not difficult to determine.
Simply hook a DVM onto the 1st cap from the rectifier and power it up.
The initial startup voltage will peak, then level off as the circuits draw current.

Re: Cap substitution in Rockola 414 amp rebuild

Posted: Sun Mar 15, 2015 9:04 pm
by cmangeng
MattTech, sorry about the significantly delayed response and thank you. I ended up replacing the cap with the recommended value and just ordered it. Amp is working great now. Always appreciate you and all the others that take the time to provide advice and guidance.
I am now working on a wurlitzer 2500 that is misbehavin and will probably need some insight into possible solutions after I have some time to try all the recommendations in the manual. Craig.