Help with SB-301

[Mark Graalman WB8JKR]

  Thanks for the input Dave, I think I got her
going now. I couldn't really find anything "wrong"
So I took out the original AGC diodes (D3 D4)
and replaced them with two Shottky diodes
and changed C114 to 20 pf, re tuned the I.F.
transformers and WOW, the AGC action is
absolutely perfect!
 The original AGC diodes had a junction
voltage of .670 volt (measured) and the
Shottky's have a measured junction voltage of
.360 volt, the lower turn on coupled with a little
extra input to them by the increased coupling
really makes it work well.

Mark  WB8JKR


On Sat, 6 Jan 2001 21:48:20 -0500 "KD2E" <ham at cybercomm.net> writes:
> 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>
> 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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