Looking for some suggestions on what to check before I send my Alpha 86 to
Colorado for repairs. It's been reliable workhorse since around 1990.
In CQWW SSB it was being used as the run station on 10m SSB (28.7 or so,
but SWR is fine) when smoke started to pour out of the top (through the
blower exhaust holes above the finals). It was quickly turned off - the
protection circuits didn't kick in. Inspection showed only one obvious
problem inside. The plate choke had overheated - and near the middle of
the choke it looks like the winding got very hot and the core material
(plastic of some kind) smoked. A particularly pungent smell...
So, I ordered a replacement plate choke the next day which arrived a few
days ago. Tonight I replaced the bad choke with the new one and turned the
amplifier on. After warmup, I fed it a 25w from my FT1000mp and things
seemed just fine. Increasing the power slowly it went past 600w output and
then blew the two 20a 250v fuses. The protection circuits didn't kick in.
So... I'm looking for some suggestions on what I might be able to check
out. Obviously I don't want to ship it to Colorado (what kind of
turnaround time can I expect if I have to?) and would like to have it for
CQWW CW in two weeks... The amplifier has the original pair of 3cx800
tubes. The power supply capacitors check out OK. The power supply
voltage is fine at 2500v+. No excessive grid current.
73 Tom
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e-mail: frenaye@pcnet.com YCCC --> http://www.yccc.org/
Tom Frenaye, K1KI, P O Box 386, West Suffield CT 06093 Phone: 860-668-5444
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