[ARC5] Using BC-454 as backend

[Ian Wilson]

Or - at last! - a use for the RBM that has been sitting here forlornly for
a while!

73, ian K3IMW

On Thu, Jan 25, 2018 at 6:57 AM, Ian Wilson <ianmwilson73 at gmail.com> wrote:

> 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 that I made for the XYL to listen to BCB news - superseded by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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