[AMRadio] stock or mod


Todd, KA1KAQ ka1kaq at gmail.com
Wed May 31 15:03:07 EDT 2006


On 5/31/06, Donald Chester <k4kyv at hotmail.com> wrote:

> I have two 75A4's.  Bought them in the early 80's.  Paid $200 for one and
> $100 for the other.  In stock condition, the receiver has excellent
> stability, sensitivity, selectibility and dial calibration.  But
<snip>
> However, the 'A4 can be converted to as good an AM receiver as its
> mechanical filters will allow, with a few REVERSIBLE mods.

Some very good info in your post, Don. I have two A-4s right now too,
only because they both belonged to interesting individuals, one of
whom worked on the Manhattan Project. This is the receiver I'm using
now, and it has had some mods done to it that include different tubes
in some of the sockets and probably a lot more underneath the chassis.
I'm actually going to be digging into this one over the weekend at
'UJR's place to cure a few other issues, so I'll print this posting
and take it along.

The other receiver is stock and has a nasty hum that wasn't cured by
replacing the filter caps. I have a spare Hammond choke for it, just
in case. Time just hasn't permitted further work on it.

I think a lot of the modified units out there were done in a time when
the rigs were a dime a dozen, not unlike the Command sets hacked up by
the thousands. They were $2 or so NIB, and the supply seemed endless,
so what was the big deal? It's a much different world today, which is
why I'd just as soon pick up another receiver than try to re-design
one into something it wasn't designed to be. If I can make simple
changes as you've mentioned here, great. If it requires major surgery,
no thanks.

Collins does seem to have gone out of their way at times to restrict
audio. I understand not putting a lot of effort into the audio of the
51J, for example, by making it push-pull like the Super Pro or SX-28.
Not really cost-effective for gear made for communications, not
entertainment. Maybe that was the same thinking with the 75A-4?

Then again, Hallicrafters didn't use push-pull 6V6s in their FCC model
of the SX-28, either.

~ Todd,  KA1KAQ



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