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Author Topic: Help with R390A audio section  (Read 17999 times)
KC4MOP
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Posts: 960




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« Reply #30 on: December 22, 2013, 04:44:07 AM »

I don't think that I've ever had a choke go bad, so it's interesting that you've lost three. Could be someone trying to 'cheapen' things in production without reference to engineering......Someone in purchasing doing that in buying the dynamotor/cooling blower motor in a radio led to about 7 RAF jet fighters being lost back in the 1960s....
I looked back to the beginning of this thread and the OP stated that he has two 390A's and one or both had a ripple problem and one or both radio sets were solid state P.S. So the higher voltage and todays "110 VAC" which is really close to 130 VAC is way beyond the original specs.
I run my 390A on an old TV isolation transformer set for 110 vac., since I have owned the radio. Runs flawlessly 24/7. There have been age related issues with a tube here and there. The 26 Huh? tube rectifiers needing replacement. Still available at Antique electronic Supply...Price doesn't stop me....always have spares in my tube caddy.
The filters on the audio module replaced and some RF coils burning up from stray RF getting into the front-end. (my bad). It's like a Timex watch. Keeps ticking and ticking.
And N3DT you are very resourceful to actually re-wind those filter chokes.
You should lower the input operating voltage to 110 vac. and re-install the tube rectifiers
Fred
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N3DT
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Posts: 1345




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« Reply #31 on: December 22, 2013, 06:08:35 AM »

I'm pretty sure it was a short somewhere causing lots of current through all the chokes.  The AF B+ choke was burned and swollen and lots of stuff in the AF area was charred/dark, so it may have been something in that area.  And that would suck current through all the chokes.  Probably no fault of the chokes themselves.
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