[Hallicrafters] Hallic. SX-24

[Joel R. Hallas]

I think Roy is on target here. I had problems with grounds on my (former)
SX-25, especially with respect to the riveted tube sockets. I suggest measuring
the resistance between each tube socket ring and chassis. If you get ANY
resistance greater than 0.0 Ohms, corrosion has occurred and/or the rivet has
loosened. My fix was to run a lead from one of the socket lugs to a solid
ground, preferably one with a bolted lug, such as on a terminal strip. I also
found resistance between the tuning capacitor rotor and the frame which yielded
to contact cleaner on the wiping springs. Just 'cuz it looks grounded doesn't
make it so!

Hope that helps!

GL & 73, Joel Hallas, W1ZR

Roy Morgan wrote:

> At 01:43 PM 8/7/02 -0700, k7mks wrote:
> >Am restoring a SX-24 and find that Vg to the 2 IF tubes (6sk7s) run -9
> >to -20VDC instead of the usual slightly negative.  Vp & Vsg are OK.
> >Removing the 6H6 DET/AVC has no effect on this high negative voltage which
> >also appears on the RF amp. grid.  All caps have been changed. Tuning
> >through an AM station it sounds like the BFO is ON  when it is not.
>
> BINGO!!
>
> Your IF is oscillating.
>
> Check bypass caps, all ground points and especially whether the radio has a
> glass tube installed where a metal one with pin one grounded should be.
>
> You have a feedback path you must find and cure.
>
>    The
> >source of the high negative voltage on AVC line has me puzzled.
>
> Negative grid bias caused by an oscillation.
>
> Roy
>
> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> roy.morgan at nist.gov --
>
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