The AM Forum

Ran this SX100 for four years now with my Champ.

Recently I have noticed a problem. 

When AM signals come in strong like 30 to 40DB over, The carrier is strong but the audio from the station comming in is weak and low. So low that I have turn the volumne way up to half or more on the dial to hear them.  The Stronger the station the worse this condition is. If a station comes in at 20 DB or less, The audio is louder. This seems to be a function of the AVC.

If I turn the RF gain down, I cant hear at all.

If I turn the AVC off,  I get a HUGE increase in sound (normal).  I can then dial the RF gain around to get people very clear like the set used to do.

I checked tubes.  What would cause the AVC to really lower audio down that low?

Leaking coupling cap from the detector to the first audio.  AVC voltage is starting to cut off the audio tube, I'm willing to bet.  Or could be leakage to ground in the AVC circuit.

Also there's a .047 in the ANL circuit, that if clipped out, will greatly improve audio distortion at the expense of ANL action. 

Thanks alot for the help.. I guess its time for an overhaul. It worked for years sitting here..   I will check and or replace the caps. 

For now, I hooked up an old FRG7.. Hey.. Not a bad little RXer!  In comparison to the broken SX100!

C

But you will miss the handy selectable sideband until you get your SX-100 again.

If the caps are original, you probably have a lot of black beauties in there.  To get to the ones on the selectivity switch, you only need to unsolder one lead from the back of the switch and then it slides back far enough for easy access to the caps.

Check your 1600/1700 KC second conversion crystals  to make sure they are on frequency.  The second IF must be aligned at 1/2 the difference between the two crystal frequencies plus .75 khz. for the adjustable selectivity and selectable sideband to function as intended.  If the crystals have not drifted very far it is easy to slightly readjust the alignment frequency for the low IF and BFO to account for this drift.

Rodger WQ9E

Ok thanks for the tips.   Maybe this weekend I will find time to go through the Rig.  The Frog is not bad but my side band does not work on it. Just am.  Pobably has missing filters..


C