SB401 Problem

[Stu Lyon]

The advice Mike Bryce just passed on is excellent. (The tick is 50 mA.)

However, should it not help, another place to check is R401-47K which
provides the unbalance current to the balanced modulator in the TUNE mode. I
have found this resistor had drifted high in a couple of rigs. I recommend
that it be changed to something like 33K. The resistor is the front-most
resistor on Terminal Board 2

Once you get it working in the TUNE mode, you'll probably find that the 200
ohm balance pot has gone bad and won't balance in the SSB modes. As a matter
of course, I replace this pot with a 10-turn trimpot mounted on the top side
of the board.

Good luck es
73, Stu W6CUX
Winnetka, CA
slyon at pacificnet.net


----- Original Message -----
From: "The Pollacks" <rinkies at CTS.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Saturday, December 29, 2001 5:16 PM
Subject: SB401 Problem


> I am putting my old SB401/303 back on the air after several years of
> storage.  Got the RX going great, but the 401 has some problems:  Mostly,
> the output is very weak (100 ma plate current) and unstable.  I cleaned
the
> switch contacts and relay contacts with tuner cleaner, but no help.  Could
> the finals be weak, or ???
>
> Any ideas appreciated.
>
> Thanks
>
> Ron K2RP
> Rinkies at cts.com
>

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