[R-390] r390 carrier pot faliure

[David Wise]

That fixed resistor will be fine until a couple of tubes age or get
replaced.  Then you will be stuck with a not-quite-zero and no tweak.

There are two or three different low-ohm pots available cheap from Fair
Radio that are appropriate for the R-390(*).  Check their website.
Exact model numbers are in the archive, I posted on this about a month
ago.
It doesn't need to be an exact replacement in this particular
application,
anything from about 10 to 20 is fine.  (Above that will work too, but
the
adjustment gets progressively more finicky as you go up.)

It's also possible to modify the circuit so that a low-ohm pot is not
necessary, but the final writeups aren't out yet.

Dave Wise


-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net] On Behalf Of Scott Bauer
Sent: Friday, October 12, 2007 8:21 PM
To: R-390 List
Subject: [R-390] r390 carrier pot faliure


 The carrier pot wiper fell out of my R-390 and I have been having
trouble locating a new16 ohm pot. I put in a 100 ohm 10 turn pot and
then zero'd the meter. I then removed the pot and ohmed it out. It
measured 8 ohms.
I had a 7.5 ohm resistor in my junque box so, what the hell. I soldered
it up and my meter sits exactly on zero when I turn the rf gain all the
way back. I am thrilled and plan to keep it in place. I may put the pot
in just for looks. Nobody will ever know. So there is my 16 cent science
project for the day. I can now use my 390 without the needle pegged
against the 100 stop.
  AES used to sell a 16 ohm pot but no longer stocks them. Fair stocks
them but they are used. Who knows how long it will last.
 
Scott
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