[ARC5] Using BC-454 as backend

[D C _Mac_ Macdonald]

I used an R-25/ARC-5 for the fixed I.F. for a Morrow 5BR-1 converter as my primary station receiver for several years in the mid-1050s.  I believe you would be happier from a selectivity standpoint going that way instead of trying to convert your BC-454 I.F. to 1525 kHz.

73 de Mac, K2GKK/5
(Since 30 Nov '53)
Oklahoma City, OK
USAF Retired 61-81
FAA Retired 94-10


________________________________
From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> on behalf of Ian Wilson <ianmwilson73 at gmail.com>
Sent: Wednesday, January 24, 2018 20:45
To: ARC5
Subject: [ARC5] Using BC-454 as backend

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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