[Hallicrafters] SX-101 Mk III Overload / Desense

[Ian]

Jim,

Well, wouldn't the with and without AVC mean that the "with AVG" isn't
really working????

What did you find when you measured voltages in the AGC circuitry?  

Ian, K6SDE




>-----Original Message-----
>From: hallicrafters-bounces at mailman.qth.net [mailto:hallicrafters-
>bounces at mailman.qth.net] On Behalf Of Andrew, Jim - BD
>Sent: Thursday, December 02, 2010 5:42 PM
>To: 'hallicrafters at mailman.qth.net'
>Subject: [Hallicrafters] SX-101 Mk III Overload / Desense
>
>Hello All,
>
>I have been restoring an SX-101 Mark III. The good news - this is a hot
>receiver, looks great, and with a small exception everything works. The
>bad news - when I tune through a strong signal ( like the crystal
>calibrator output) something overloads in the receiver and the signal
>goes to near zero. I can recover the signal by simply tuning away (10-20
>kHz) or by turning down the RF gain. The problem is noticeably worse on
>LSB than USB even though I recalibrated the BFO to 50 kHz and signal
>strengths are similar for both sidebands.
>
>At first I suspected an AVC problem, but the event happens both with and
>without the AVC engaged. It sounds precisely like what happens during
>alignment of the 1600 and 1700 kHz 2nd Converter Oscillators so I have
>gone through that procedure several times, only to find I have
>aggravated the situation.  Adjusting the crystal activity slug while the
>signal is muted does not seem to help.
>
>Have only peaked the 50.5 kHz IF by ear - wondering if that might have a
>role in this. I have a replacement 12AT7 2nd Converter Oscillator tube
>on order, but in order to properly troubleshoot I would appreciate
>comments anyone might have on the circuit theory, either in this stage
>or elsewhere, that might cause such a problem.
>
>Thanks in advance for any thoughts or similar experiences you might have
>had.
>
>Two steps forward, one back. At least the tubes keep the shack warm.
>
>73,
>
>Jim, K5UI
>
>
>
>
>
>______________________________________________________________
>Hallicrafters mailing list
>Home: http://mailman.qth.net/mailman/listinfo/hallicrafters
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:Hallicrafters at mailman.qth.net
>
>List Administrator: Duane Fischer, W8DBF
>** For Assistance: dfischer at usol.com **
>
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html