[Hallicrafters] SX-101 Mark 2B -

[Peter Bertini]

Sounds like the BFO energy is leaking into the AM detector, and causing a
bit of AGC voltage. As information, most CW operators run these old
receivers with the AGC off and volume set on the high side, and manually
ride the RF gain for a comfortable listening level. What you are seeing
isn't unusual.  A cure would involve shielding the BFO circuits with better
decoupling, and perhaps going to a balanced product detector to minimize BFO
blowby.

Pete

On Sat, May 22, 2010 at 12:33 PM, jsloss <k7mks at comcast.net> wrote:

> Would appreciate commments from those  Mark 2 owners who have corrected the
> following glitches:
>
>  With antenna grounded to chassis, RFG full CW, AM mode selected, the
> S-merter can easily be set to indicate zero.  When switching to CW/SSB mode
> the meter pointer moves upscale to S 2 or so.  It can be re-zeroed but then
> the AM zero is off.
>
> I should mention that I have replaced V7 6BJ7, V8 6SC7, C-93.  The PITCH
> control slightly affects the S-meter zero when in CW/SSB mode.
>
> The set has been given a correct 1650 and 50.750 Kc IF alignment.
>
> Second concern is mechanical stability with in CW/SSB above10 MCs or so.  A
> light tap on the panel, cabinet or chassis will cause a "warble". .  This
> may be a characteristic of the S-76, SX-96 and SX-100's as they are similar
> and warble with a mechanical "tap".  At least mine do!
>
> Thanks for forthcoming advise.
>
> Joe k7mks
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