HX-20 Low Audio

[Guy G. Giacopuzzi DDS]

Al Waschka wrote:
>
> Fellow Heath'ens -
>
> I am restoring an HX-20 to go with a Drake 2-B to replicate my first SSB
> rig.  I got the HX-20 along with an HR-20 receiver and an HP-20 power
> supply at the local hamfest for $50.  They are a little rough, but they
> should clean up OK and after a little touch up paint on a few front
> panel scratches and repainting the cases they should look like new.  The
> receiver had a problem in the S-meter which I fixed and could use an
> alignment.  The power supply was missing the indicator lens.  The
> transmitter didn't seem to work at all.
>
> I have been through the HX-20, found and fixed several problems (open
> resistor, bad LSB crystal, cracked slug) and aligned it. Power output
> seems low (40 watts on 80, 40, and 20, decreasing to about 10 watts on
> 10 meters.  The heterodyne oscillator voltages are low (about 60% of
> what the manual says) but the tube checks good.  Except for the low
> output it seems to be working on CW but not very well on SSB.  At the
> moment I do not have an LSB crystal, so I have performed all steps with
> the USB crystal in the LSB socket.  Since this oscillator is after the
> crystal filter, I don't think it makes any difference.  After all
> alignment I returned the crystal to the USB socket and operation in USB
> is identical to that previously in LSB.
>
> I have been through the entire alignment process with no abnormal
> indications.  The "carrier null and sideband frequency adjustment"
> process on page 82 where you set the carrier oscillator so that the
> power output is 1/8 scale works.  The power output with the modulator
> unbalanced and the frequency tuned off is about the same as with the
> audio gain set at CW which bypasses the filter.  This all seems to
> indicate that the filter and V4A are OK.  The carrier also nulls out
> which seems to indicate that the balanced modulator is working OK.  In
> SSB I can just barely see the output meter wiggle with the audio gain
> wide open. The meter is full scale with the audio gain set at CW.  V1,
> the audio amplifier and modulator driver checks OK on a tube tester and
> by substitution. Two microphones work about the same.
>
> Maybe a coupling cap bad or something.  Does anyone know what level
> audio should be getting coupled into the balanced modulator?
>
> Does anyone have any other ideas?
>
> Thanks,
>
> Al K5TAN
>
> --- --- --- --- --- --- --- --- --- --- --- --- --- --
> To subscribe: listserv at listserv.tempe.gov
> and in body: subscribe HEATH yourfirstname yourlastname
> To unsubscribe:  listserv at listserv.tempe.gov
> and in body: signoff HEATH
> Archives for HEATH: http://www.tempe.gov/archives
> --- --- --- --- --- --- --- --- --- --- --- --- --- --I'm not so sure that "40 watts" is low.  You only have 90 watts input.
Have you tried changing the final?

ggg

--- --- --- --- --- --- --- --- --- --- --- --- --- --
To subscribe: listserv at listserv.tempe.gov
and in body: subscribe HEATH yourfirstname yourlastname
To unsubscribe:  listserv at listserv.tempe.gov
and in body: signoff HEATH
Archives for HEATH: http://www.tempe.gov/archives
--- --- --- --- --- --- --- --- --- --- --- --- --- --