The AM Forum

If you are having a really bad luck day you don't even need tubes and high voltage to send copious amounts of smoke into the air.  My little transistorized Chinese 139A receiver made a lot of smoke for a battery powered radio that is only 7 inches tall, 10 inches wide, and 4 inches deep including the clip on battery case. 

This morning I pulled it out of its case to correct an annoying dial calibration error and gave it a complete alignment (fortunately you don't have to read Chinese to follow a schematic!).  After alignment I left it running on the bench while I went upstairs to refill my coffee and when I got back to the basement Siam Sam (the radio room cat) was doing his best mournful Siamese cry while heading away from the smoking radio.  One of the transistors in an intermediate audio stage developed a hard internal short and was melting the plastic sleeve over the transistor.  After killing the power I ended up replacing the bad transistor, a nearby electrolytic that got its case singed, and sleeved a connecting lead that had the insulation damaged. 

The 139A is a neat little radio and I used it a couple of days ago with my Viking 1.  It sounds pretty good on AM and works OK on CW although the selectivity is a bit broad.  The Chinese made it pretty easy to service with a complete manual and a separate long cable from the power supply to allow testing and alignment when the receiver is out of its case.

It is in the picture with is older relatives, a type 139 receiver and matching transmitter.  These are the "red" version of our "Angry 9".

Rodger WQ9E