SB-401 Problem

[Edward Swynar VE3 CUI]

Ed...

Is it a problem only on USB? LSB? Both...?

Those HC6/U carrier crystals DO change over time---perhaps if it was only
one sideband, versus the other, I'd suspect that the ssb carrier frequency
is out of (or close to being so) the passband of the crystal filter.

I had similar trouble once with my SB-400---first sign of trouble was that
I never could adjust the LSB frequency to match that for USB (by way of the
variable inductor at the back of the LMO).

If I recall, LSB audio on recive was tinny & thin---ditto for transmit. A
check proved that the carrier crystal for LSB had SHIFTED some 1.8 KHz over
time! The repair was simple enough, i.e. a new LSB crystal.

Try listening for the crystal carrier frequency on a well calibrated,
digital read-out general coverage receiver to verify this---it will be
quite weak, so you will need to run a short wire from the receiver antenna
jack close to the crystals inside the Heath rig.

Good luck, & keep us posted on your progress!

~73~ Eddy VE3CUI - VE3XZ




----------
> From: Ed Richards <k6uuz at JUNO.COM>
> To: HEATH at LISTSERV.TEMPE.GOV
> Subject: Re: SB-401 Problem
> Date: July 17, 1999 12:34 PM
>
> I don't know what you have tried but SSB power is hard to measure. Try
> whisteling a sustained note while checking power , plate current, etc. It
> is normal to get less power indicated on SSB.
>
> Ed Richards
>
>
> On Sat, 17 Jul 1999 17:47:24 -0400 "Paul R. Young" <youngpr at HIS.COM>
> writes:
> >I've got an SB-401 with a problem that is stumping me.  I get full
> >power
> >out on CW but only a small percentage of full power output on SSB.
> >Microphone trips the VOX normally.  I understand that the SB-401
> >unbalances
> >the balanced mixer in CW mode.  Anyone have an idea for me to try?
> >I've
> >substituted tubes, changed out the balanced mixer diodes, etc.  I'm
> >open to
> >suggestions.
> >
> >Thanks.
> >
> >Paul
> >
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