[ARC5] Using BC-454 as backend

[Ian Wilson]

Thanks all for the helpful suggestions.

I have a setup here with a BC-946-B + power supply/speaker
that I made for the XYL to listen to BCB news - superseded by
superior quality news online from NPR :(

Just did a quick tuning test - the 946 will tune at least 10kc above the
dial end-marker indication (1.5Mc). So this is obviously the simplest
solution, and will achieve the goal of giving the Morrow converters some
air time.

I will still see if I can get the BC-454 working as a backend because
I don't feel like giving up. And there are several hacked BC-454's
around here that would be happy to see some life as future projects.

Will report when/if the Morrows are working.

73, ian K3IMW

On Thu, Jan 25, 2018 at 1:09 AM, Leslie Smith <vk2bcu at operamail.com> wrote:

>   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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