[HBR] Restoring old receiver

[Dan Merz]

Stan,  I would argue against spending too much time refining old receivers and
ending up with something that might work a bit better but will be of little interest
to anyone in the future.  I have similar radios that I have resisted the temptation
on "improving".  I've found that I can find an unmodified set of later vintage and
appreciate it for its features.  There's always going to be some maintenance duties
to make it work like it should without changing the basic circuitry to satisfy the
tinkering urge.  AC/DC sets are pretty safe,  particularly the ones made by
National,  Hallicrafters etc.   You can always use an isolation transformer for
added peace of mind and safety when working on them and operating them.   I can
appreciate that you may have what looks like a beater that no one would want to
collect,  though I hardly recognize the term "collectible grade" since for every
condition there's a price and someone who would want to have it at that price.  I
don't get too excited about having a radio that  looks like it was never used unless
I made it that way from something less attractive.    By the way,  I once replaced
every original 55 year old capacitor in a National NC-200  and found that the
improvement was nil over replacing the two or three that had obviously failed and
were causing obvious problems,  like hum and grid voltage. Of course, some of them
might have gone south the next day but I operated it quite a bit before taking the
plunge.   For ssb,  a product detector is a godsend,  not that it sounds that much
better or gets you more signals than a diode detector,  but because it can handle
big signals without distortion and is friendlier to AGC.  Don't ignore the agc
aspects of ssb product detection if you are going that route because that's what
makes it so nice in my opinion.  Otherwise,  you'll be riding the gain control just
like you have to do for a diode detector with weak bfo injection.

After all this,  I would say that it is appealing to make something perform better
like you propose - I'm probably not very good at it so prefer to work with the
original designs and satisfy my interest mostly in that manner.  I have done some
homebrew stuff but not too different than handbook published sets.  If I were going
to be "stuck" with the set you have,  I would build an external power supply (i.e.
isolation transformer).  One very good radio that is AC/DC is the Hallicrafters
S-22R which is even older than yours - it's only annoying flaw is a bit of
modulation hum on ssb signals that I haven't been able to get rid of,  gets worse on
20 meters.  Of course its selectivity is  bad but it's still fun to use.  Good luck
- I can't offer any advice relative to adding a Q5er to your set from my
experience,  Dan.

Stan Wilson wrote:

> I recent acquired an old receiver from the late 1940s that is not
> collectable grade.   Every cap in it needs replaced plus several  tubes.
> It is a National and the  basic design was no doubt state of the art for
> a AC/DC receiver in that era.  I am considering redoing all of the caps
> and rewiring the tubes for a filament transformer and also using a
> reverse filament transformer to generate the DC.   Other choice is what
> to do about the detector stage.   My first thoughts were to replace the
> 6H6 with a 6BE6 product detector, but after consideration think maybe
> the better choice is to restore everything electrical with the improved
> power supply circuit and add a RF connector to go to an external Q5er.
>
>
>
> After all of the rework it will still not be a collectable quality
> receiver, however, it will look original, and be an excellent test
> receiver (and safe with the isolated power supply) for my work bench
> that I can also use to listen to SSB activity on the bands or the local
> AM stations.
>
>
>
> Wonder what others have done in similar cases ?  Have you used a oldie
> as the foundation for a HBR or improved one ?
>
>
>
> de stan ak0b
>
>
>
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