HW101 oscillation/carrier supression

[Stu Lyon]

I'll bet it's a bad carrier balance pot. This is a 200 ohm pot and is
infamous for going bad. My 34 yr old SB-101 that I built back then suddenly
showed up with the same problem. The fix is to replace the pot with a
19-turn 3/8" x 3/8" trimpot. They have three wires out the bottom and a
screwdriver adjust out the top. There are other arrangements but this is the
one you want. The wires are spaced at .1" which is a little narrower than
the original but you can spread the wires to match. The pot should mount on
the component side of the board. You should also replace the 220 ohm
resistors at the same time.You can find the pots in the Mouser catalog (on
pg. 239) for about $1.20. P/N 72-T93YA-200

I have replaced about 10 of these pots in various -401s & -101s and it is
always the fix for the problem you describe. If you can find them, the HP
5082-2805 quad-matched diodes are a good replacement for the balanced
modulator diodes.

Good luck
73, Stu W6CUX
Winnetka, CA
slyon at pacificnet.net

----- Original Message -----
From: "John Wb5Oau" <johnmb at MINDSPRING.COM>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Saturday, July 21, 2001 1:23 PM
Subject: HW101 oscillation/carrier supression


> I'm working on a recent acquisition that "worked perfectly" (and might
> have, if CW is all one used).
>
> The issue is, on 20m (have not checked other bands) if I set the driver
preselector such that it peaks the output (and the receive
> sensitivity) there's about a 10W carrier that is present when
> keying the mic in either sideband. Tuning slightly off frequency
> (w/driver preselector) makes it go away...but then it  takes
> the drive away too!
>
> I vaguely remember such a problem with my original 101 (that this
> is to replace).
>
> Any hints? I know that the two variable caps that the Driver/Presel
> tunes are "in synch".
>
> Where to go first to fix such a thing? I have not tried it on
> other bands to see if this is an issue. I just fixed the dirty bias
> pot that prevented proper setting of the bias. There's lots of signal
> (nearly 100w out on 20m) so the rig is working well. Modulation looks
> fine too, if I could just get rid of the oscillation/unwanted carrier.
>
> Any and all help gratefully appreciated.
>
> Rgds
> John wb5oau/4

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