sb-303 LMO problem

[Edward Swynar VE3 CUI]

I wonder if there's a similar "fix" for the SB-300 receiver...?

Mine has the 6AU6 tube in it, & it has the most annoying habit of suddenly
drifting some 3-5 KHz in a matter of about 3 seconds after having been
warmed-up for a half to a full hour. I then replace the 6AU6 tube, & it
might drift a KHz or so, but then it stays locked on frequency for
(literally) hours & hours on end...

Now, when I turn on the rig the next day, the same thing happens with this
second tube in place---I swap in the ORIGINAL first tube, & history repeats
itself, i.e. I pull out the second tube, put in what was the original, & it
stabilizes...

I just don't get it! But, I like the rig so much, I keep both 6AU6s handy.
& merely swap them when the cursor needs a (sudden) drastic re-adjustment.

Say---what does that small thing-a-ma-jig that looks like an adjustable
inductor (right alongside the LSB LMO adjuster) do? Is it some kind of
temperature compensating tubular capacitor/inductor to prevent these sudden
excursions? Nobody seems to know in past queries I've made here---I guess
most folks equate the LMO "black box" with black magic (the warnings from
Heath regarding voided warranties didn't help!) and never venture
therein...

~73~ Eddy VE3CUI - VE3XZ




----------
> From: George T. Baker <w5yr at SWBELL.NET>
> To: HEATH at LISTSERV.TEMPE.GOV
> Subject: Re: sb-303 LMO problem
> Date: August 30, 1999 4:07 PM
>
> Tough news, Rick.
>
> I went through my SB-303 manual and nowhere could I find any details
> about the LMO, especially not a schematic.
>
> Sorry . . .
>
> 72/73, George        AMA 98452          R/C since 1964
> Amateur Radio W5YR, in the 53rd year and it just keeps getting better!
> AutoPOWER Systems, Fairview, TX (30 mi NE Dallas)  Collin County
> QRP-L QRP-ARCI FISTS NORCAL ZOMBIE ARS 10-X  33.2 N 96.6 W EM13RE
>
>
> Rick Booth wrote:
> >
> > I have a sb-303 with a LMO that appears to have gone goofy.  It works
ok for about the
> > first 25 KHz, gets severly distorted for about the next 25 KHz and then
gives up entirely.
> >
> > I need a schematic if that is possible.  That will save me the hassle
of tracing out
> > whatever is lurking in that dang box.
> >
> > Thanks in advance.
> > Rick
>
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