[ARC5] Using BC-454 as backend

[Leslie Smith]

  Hello Ian,

  I have a BC band receiver - ARA type, I think.
  When I got it, it worked fine.  
  Over a period of months, being in daily use it slowly became unstable
  - if it would oscillate when tuned to a station.
  The put the set aside without diagnosis.  If I had my druthers, I'd
  say a cap (or two) dried out over the months it was in use.  I put the
  instability (as a guess) down to the I.F. strip.  David Stinson's
  advice about re-capping is gold!
  All the best!

   73 de Les Smith
   vk2bcu at operamail.com



On Thu, Jan 25, 2018, at 13:45, Ian Wilson wrote:
> I am working on using a BC-454 as backend to a Morrow converter. The
> Morrow produces 1525kc for a BC band car radio as backend. My plan
> is to use the BC-454 with IF and BFO tuned up from its original
> 1415kc.> The idea is to make 100% reversible changes only.
> 
> So far I have dug out and reanimated a BC-454. This works OK as a
> receiver -> tested with 4MHz input. Tested all the tubes - all good except a
> dead 12SK7.> 
> So the next step was to remove the RF amplifier and converter
> tubes and> tap into the input to the first IF transformer. This appeared to be
> working OK.> 
> Next step is to retune the BFO, align the IFTs to 1525kc
> (obviously I don't> know whether they will pull this far. If not, have to think of a Plan
> B). However,> came across a problem - if I retune the BFO too far it apears
> that the IF> strip itself starts to oscillate. Not sure whether I am diagnosing
> this correctly.> 
> Perhaps a screen bypass capacitor in the IF stages? There is
> some sign of> leakage from some of the metal can capacitors.
> 
> Originally I left the primary of the 1st IFT floating. Bad idea.
> However, putting> a few kOhm (with series 0.01u cap to keep the HT happy) to
> ground made no> difference whatsoever.
> 
> I'm sure numerous people over the aeons have trodden this path.
> Interested> in any suggestions.
> 
> 73, ian K3IMW
> 
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