[R-390] 3TF7 Substitutes

[Dallas Lankford]

Thank you, Tom.

No, I have not seen a spec on frequency shift vs. line voltage change.  If
you find it, I would like to see a copy.

For a stock R-390A and the usual applications exceptional stability is not
necessary, just as my BFO vernier fine tuning mod is not rerally necessary.
But if you like your SSB to sound like AM, then the fine tuning mod is a
step in the right direction.  And the remaining step (there may be a 3rd if
I can figure out where this slow +/- 1 Hz or so drift is coming from) is the
3TF7 replacement with a 12 VDC regulator.  Then when your AC or 50 amp
electric CH kicks in, the SSB tone (or CWS tone) won't change.  And when the
fellow you are listening to drifts off 5 or 6 Hz, you will know it is him,
and not because your house line voltage drifted off several volts.  For ECSS
(which hams seldom use, but which is a mainstay of AM DXers), staying on
frequency is important for obtaining the best recovered audio from difficult
DX.

As for spookland, there is no telling what they are up to.  But it wouldn't
surprise me if they didn't still have some rooms full of R-390A's.

Best regards,

Dallas

----- Original Message -----
From: <wwarren1 at nc.rr.com>
To: "Dallas Lankford" <dallas at bayou.com>
Sent: Friday, September 24, 2004 12:38 PM
Subject: Re: [R-390] 3TF7 Substitutes


> Dallas,
>
> 10,000 thanks for publishing your results.  Those are exactly the types of
experimentation and subsequent analysis that help the hobby. (That is, as
opposed to some witchcraft that somebody thought appropriate, seemed to work
for him, but was fundamentally wrong all the time.  We see enough of those.)
>
> I think I ran across a spec for the R-390A as built by Hammarlund (thus
EAC) where they quoted 30 Hz or so shift in received frequency when the line
voltage varied from 90 volts up to 120 volts.  I'll see if I can find that
spec and pass it on.  You may already have seen this spec yourself.
>
> But except for really critical applications (I don't know, maybe 16
multiplexed TTY channels) in the 1950's, even 30 Hz shift shouldn't be too
much of a bother.  But then in some Black application of the radios, I could
be way off base.
>
> Very best and thanks for your report,
>
> Tom, W4PG