Date: Tue, 24 Nov 2015 00:41:41 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] Alpha 76 question
Ted,
> My Alpha 76 periodically "snaps" loudly (arcs?) when idling...maybe
> every 20-30 minutes. Any ideas what this may be?
I don't know anything specific about that Alpha, but I have seen this kind of
arcing at regular intervals when there is a simple power supply that has no
bleeder and no load on it. There are very often lots of very narrow but tall
spikes riding on the power line. When there is no load at all on a power
supply,
these will slowly charge the filter capacitor to such an overvoltage that
something arcs.
So I would suggest to check all bleeder resistors, first of all.
Manfred
## IF ANY of the EQ resistors across ANY of the electrolytics ever opened
up, that one electrolytic would blow up, its voltage drop across it, with NO eq
resistor,
would rise to the full B+ level. If any of the EQ resistors value, drifted
way up in value,
its V drop across that cap would also rise sky high.
## It would be wise to check all the caps anyway, and perhaps replace the
entire string
with modern new variety. I would check and probably replace the EQ resistors
on
spec with modern 100K @ 3 watt MOF types, like 1-5% tolerance. You can
get the
100K @ 3 watt resistors from Rich measures, AG6K, who will also hand match
them for you.
You can also buy them from mouser, in 1% tolerance. The 1% ones I bought from
mouser all ended
up being the exact same value, 99,980 ohms...all 300 of em, in boxes of
100..and 3 different lots.
## Find out where the arcing is coming from 1st. It could be as simple as
dust bunnys, or other debris in there.
Or misc junk in there somewhere. You could also pull the tubes, and see if
the arcing still occurs. It could also be
HV wiring that has shifted. I have also heard the arcing myself, on a drake
L4B diode board....and one of the oem diodes
was arcing on the outside off its casing, with blue sparks snapping away. easy
fix, just replaced that one diode.
These days, I would replace the entire mess of diodes with either
1N5408s.....or 6A10s. Both use the same gauge wires
coming out each end. Both are the same body length. Body diameter is
double on a 6A10. Both are cheap to buy.
Jim VE7RF
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