[R-390] Continuing on the R-390A .........
Bob Camp
[email protected]
Sun, 09 Feb 2003 19:38:06 -0500
Hi,
Odd thing about the 10 turn pot modification. You really need a different
value pot. Strange but true ....
If you take a look the pot has a 22 ohm resistor across it. When the pot is
set to the high end the parallel combination comes out to 18 ohms. The
combination is in series with a 680 ohm resistor so it's not like they had
to do it to keep anything from burning up.
I have checked a couple of radios and have yet to find one that comes up
with more than 15 ohms for the combination of the pot and the 22 ohm
resistor. Normally they seem to run around 7 ohms or so.
If you can get your hands on a 20 or a 25 ohm pot that should improve the
situation over the stock part 3 or 4 X. Of course you would have to change
the 22 ohm resistor but that's pretty easy to do.
Another way to do it would be 5 ohm pot with a selected resistor in series
with it. Again you could use a small single turn pot rather than a big ten
turn job. Getting the 10 turn pots under the bracket can be a pain.
Take Care
Bob Camp
KB8TQ
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Sunday, February 09, 2003 2:36 PM
Subject: [R-390] Continuing on the R-390A .........
> I now have this unit completely apart and am going through
> it looking for defective parts, etc. First, I'd like to thank all
> the people who made the Y2K R2 manual available on-line.
> Really great job guys. Unit sure comes apart easily ....but I
> guess you knew that (I didn't).
>
> What I'd like to know is, what are the suggested functional
> modifications (I'm a little confused by all the postings over
> the past few years) which I might as well implement while
> it's apart.
>
> It's a 1967-68 R-390A built by EAC (parts are stamped with
> around 9/67 date codes).
>
> So far I have:
>
> 1) replace the AC filter with one that does not make the chassis
> "warm" and trip GFIs
> 2) add a 3-wire power cord
> 3) substitute modern electrolytic "innards" for C603 and C606
> 4) replace the carrier meter potentiometer with a good 100
> ohm, 10 turn, potentiometer.
> 5) add Dallas Langston's two diode AGC fix for SSB
>
> What else ?
>
> 73 Kees K5BCQ
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