Help with SB-301

[Mark Johnson/Ontario/IBM]

I've had two AGC problems with my SB receivers. My SB-310 had an
intermittent problem where the AGC would just quit, then come back.
Needless to say it was making the radio difficult to use. In the end, it
was the 6BA6 1st IF AMP tube (V6). After some time on the scope, I got it
down to the tube, replaced it and problem solved. By the way, the tube
tested Very Good on my tester.

Second problem was on my SB-301. After going from transmit to receive (I
have SB-301/401 combo), the receiver was very slow to come back...Like the
RF from transmit was/had knocked out the receiver. It had! I did some
voltage measurements with the radio hooked up and transmitting into a dummy
load, and saw that the AGC line had very high voltage on it from RF getting
into it. Traced it back to terminal strip "A" (under the RF gain pot). The
actual AGC line had never been soldered (since day one) and the line was
floating. Rig never worked right since it was built. Soldered the lead,
problem fixed.

Mark V. Johnson
VE3DJU
---------------------- Forwarded by Mark Johnson/Ontario/IBM on 01/07/2001
10:11 AM ---------------------------

KD2E <ham at CYBERCOMM.NET>@LISTSERV.TEMPE.GOV> on 01/06/2001 09:48:20 PM

Please respond to KD2E <ham at CYBERCOMM.NET>

Sent by:  Heathkit Owners and Collectors List <HEATH at LISTSERV.TEMPE.GOV>


To:   HEATH at LISTSERV.TEMPE.GOV
cc:
Subject:  Re: Help with SB-301



With the function switch on standby, the receiver mutes when the short is
REMOVED from the mute connector.
As far as the AGC....I have an SB301 whose slow agc acts like fast after it
warms up. I have another SB301 that works beautifully!  On the good one, I
opened up the LMO, and cleaned/lubricated it. The dial now turns smooth as
butter. A lot of the SB radios had kind of 'sticky' tuning. It actually
performs quite similar to my SB303.
...Dave

----- Original Message -----
From: "Mark Graalman WB8JKR" <wb8jkr at JUNO.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Saturday, January 06, 2001 9:27 PM
Subject: Help with SB-301


>   I have a Heath SB-301 that I've been slowly bringing
> back to life, I got it working pretty good but there is
> a problem with the AGC and muting. In short, the AGC
> is just about worthless, not enough AGC voltage is
> developed even with VERY strong signals and the
> receiver overloads terribly, unless I run the audio
> gain up and ride the RF gain constantly. I have
> checked the AGC diodes and even increased the
> coupling capacitor to the I.F. from 5 pf to 10 pf and
> it did almost nothing to help. Also the receiver
> doesn't mute when the mute jack on the back is
> shorted to ground.
>
>   Is this a common problem with this receiver?
>
> Mark  WB8JKR
>
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