SB-104A problem

Fri Sep 21 09:40:55 EDT 2001

Dear R. Schmitz:

Since your unit is an "A" version, a design change was installed on the
TX/IF "C" board output bandpass filters for both the 20 and 15 meter bands.
This change placed trimmer caps to tune these two filters for a flatter
response across the band.

Originally, these filters were wider in the SB-104 (so there wasn't a
problem here), but were made narrower in the "A" version to further reduce
the spurious output. By so doing, the tolerances of the components in this
filter now required a tuning "tweek" procedure. I'd check here and align
them according to the manual. This would be C333 for the 15M band, and C337
for 20M. NOTE: In some early "A"-version "C" boards, C337 was a fixed 15pF
mica. If this is the case in your unit, I'd change it to a small variable
ceramic as well.

You can try adjusting these two trimmers at the geometric center of each
band and then check the band edges for output. A re-adjustment back and
forth may be in order to maintain RF power output across the band.

Some of the early "A"-version manuals discussed this alignment procedure;
later, the "C" board was shipped factory built and aligned. There were two
manuals shipped with the SB-104(A): an assembly and an operation manual.
Anyway, this is a start towards fixing your SB-104A. If this doesn't fix
your problem, we have other places to "hunt". But then, that's half the fun.

Regards,

Dave Kechkaylo, W8DLK/9 

-----Original Message-----
From: R. Schmitz [mailto:HeathlinerSB at AOL.COM]
Sent: Thursday, September 20, 2001 7:47 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: SB-104A problem

Hello Heathkit-Owners!
Got a used SB104A and made some repairs.
Rig is fine now in RX all bands.
But TX there is a problem: Full output (SSB/CW with or without Filter) on
80,40,10 m.
Only abt 40Watt on 20 and 15m.
Driver (Power switch to LO) also only half Power on 20 and 15m.

Have only one Manual,believe there were original two?
Mine is that,with all the circuits to fold out.Miss also the Extender Board.

So repairing is a bit difficult,but hope You pass some good ideas to me.

 Power is increasing from abt 20W to 40W, if i key down a while.
So , i think, the problem could come from a switching-diode?
Or could it be in the  Bandpass in the output-line to Antenna connector?

Has anybody Ideas or (maybe) had the same problems??

Wonder why 10m has full output?

Any help is welcome!
Best 73´s de Randolf,DL6KAI

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