[AMPS] Bringing old amps back on line

Peter Chadwick Peter_Chadwick@mitel.com
Thu, 16 Nov 2000 15:33:37 -0000


Noel says:

	>What I would like to know is what steps should be performed when
>bringing an older amp back to service.

First thing I'd do is open up and give it a visual inspection. Have a look for
white gunge on the ends of electrolytics, cracked or even semi-distressed
looking resistors (especially the parasitic suppressors) and probably give it a
careful dust with a small brush. Measure the equalising resistors and change
them if they're more than 5% different. If it's got equalising resistors in the
diode chain, check those, too. Dust accumulations can lead to tracking, and dust
often gathers around the HV points. Also check things like the power cord hasn't
got insulation cracking.

If I remember that thing rightly, it's got an interlock which shorts the HV if
the cover is off the PA compartment, so make sure you put that back........

I'd then run the supply up very slowly with a Variac, monitoring the HV, and
checking for equal volts distribution across the electrolytics at something like
one quarter usual applied mains voltage. Probably go up in something like 400 or
500 volt steps in HV, and sit at each step for 5 minutes or so. When you get to
full line volts, let it soak for a while - say 10 -15 minutes before going to
tx. Don't go to tx without a dummy load connected.

I'd figure a reasonable rule of thumb is that RFout = 50% of DC in - give or
take a bit.

An extra fan blowing on the mains xformer doesn't come amiss on those boxes,
either.

Mayhap I'm just over cautious, though...

73

Peter G3RZP



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