HW-9 ?s

[John Clifford]

Greetings,

Ran into a problem today with my HW-9, and am wondering if anyone out there
can help me.

I had the HW-9 and my Drake R8A connected to amplified speakers via patch
cords, tying both headphone outputs together.  Evidently, too much
voltage/current got back into the HW-9 as its audio stopped working.
Separating everything shows that the HW-9 can barely be heard even with the
volume cranked all of the way up.

I pulled the schematic out, pulled the sheetmetal off, and started probing.
The first candidate upstream was the LM338N audio amp IC.  Sure enough,
testing for the expected voltages showed everything fine EXCEPT that the
'bootstrap' pin (#9) was putting out .5v instead of the schematic's
suggested 7.0v.  The voltage didn't change even when I tuned the radio to a
strong signal on 40m.

I'm pretty sure the problem's not upstream in the RF stages, since the front
panel meter jumps when tuning across a strong signal (verified on the R8A).

I went searching for a new LM338N, figuring that for a few bucks I'd swap it
out and see what happens.  Of course, this part is no longer made, but I've
found a source on the Net and so should be up and running soon.

My ?s:

 * If anyone with experience with the HW-9 or with electronics
troubleshooting has any suggestions on what I should be checking out, I'd
appreciate it.

 * If anyone knows of a pin-for-pin substitute for the LM338N, please let me
know.

Thanks, and please cc me a copy of your post since I may not yet be signed
up on the Heathkit list.

 - jgc


John Clifford
Weapons Safety, Inc.
13215 SE 30th St.
Bellevue WA  98005

  vox: 425-649-8623
  fax: 425-644-5302
email: johnclif at weaponssafety.com
 http: www.weaponssafety.com
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