On Sun, 14 Sep 2008 19:09:45 -0500, Ken Bessler wrote:
>When I key the new amp, the plate voltage drops from 2,350vdc to about 1,800vdc
>with the current 117v stock setup. I'm worried about the drop.
That's also a symptom of one or more bad filter caps in the HV string. Usually
there
are 8-16 of them in series, with resistors across them to equalize the voltage
across them. It's not uncommon for one or two to be bad when an amp has been
sitting
for a few years. Another symptom is a report of hum.
It's VERY easy to test these caps if you have an traditional mechanical VOM
like a
Simpson 260. Using a high Ohms scale, you should see lots of charging current
(low
resistance) when you put the probe on a cap, then decaying to high resistance
(low
current) as it sits there. That should repeat when you reverse the leads. Do
that to
all the caps, one at a time, and make a mental note of how they act. A weak cap
will
draw MUCH less charging current.
I've done this several times and replaced only the bad caps. The amps have
continued
to work well. Sometimes I'll replace one and then find a second. I've never
found a
third (in a string of 16). I've also replaced all the caps in a string when I
felt
rich. That doesn't happen often. :)
73,
Jim K9YC
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