Pearce Simpson Bengal SSB Low AM Sensitivity

[Justin B.]

Howdy, y'all! Just picked up the above radio with a few problems. It was totally dead when received and I found two exploded diodes on the PS board along with a 25A line fuse!! After replacing the diodes everything seemed fine until I keyed the mic and ka-boom, diodes fragged again. I replaced them again and found the final transistor had an E-C short so I have ordered a new transistor. I de-soldered the 2SC1307 final and am able to key up without blowing diodes and in AM mode I can easily get 100% modulation on the meter.

While waiting on the transistor I figured I could at least listen to some stuff and after a while the AM signal started fading in and out like bad QSB. I can "talk" to it with my talkie and get a good swing on the meter on all channels. There is hardly any background noise when the signal fades out. Both LSB and USB sound fine.

I see in the block diagram there are separate AM and SSB AGC sections so I am leaning toward something going on there.

Any suggestions on what I should check?

73,

 

[nomadradio]

I would start at the emitter of TR11 and see that the 7.3435 crystal isn't weak. Should see around 1 Volt peak-to-peak RF at TR11 emitter.

There are other possible culprits, but they are all downstream from the AM-only mixer TR12 where this signal feeds to. This crystal is in a socket. If you had a spare, swapping it to compare would be the quickest thing to try.

73