Allied AX/SX-190 Amateur and Short Wave Receiver Info
When I was a kid I liked to listen to short wave radio stations from all over the world on radios I built from kits and later from scratch. I eventually got a amateur radio license (expired now) and collected a lot of old radios because at the time that was all I could afford. I had old Halicrafters sets, a bunch of different military surplus radios, and eventually I got an Allied SX-190 short wave radio.
The SX-190 is a really nice SW receiver. The huge, heavy tuning dial spins ever so smoothly and it is the most precise analog tuning I have ever seen in a radio. I think it was the last of the quality analog tuned radios. After that PLLs and digital tuning took over.
A few years ago I started to wonder what ever happened to that SX-190. I guess that I must have traded it or sold it. I got the itch to get another so when I spotted one at the monthly electronics swap meet in Dallas I bought it. I think I paid $75. You can usually find them on ebay for about $100 or so.
My "new" SX-190 worked well for several months, but then suddenly died. I started looking around the web for service info and found the schematic and eventually the entire service manual. I kept looking and ran into copies of reviews and modification articles from radio hobbyist magazines. I started collecting all the info and eventually put it all together into a .rar archive file you can find here and at a couple other locations around the web.
I eventually managed to repair my radio. I traced signals through the circuits and found that one of the crystal filters in the IF stage was not passing the signal. I thought that I had a dead IF filter and started looking for a replacement. After giving up in frustration, I decided to unsolder the filter and see if I could spot anything wrong with it (fat chance!). Nope. So instead of risking losing the thing I soldered it back on the PCB. The radio started working like new again. It was a bad solder joint! Unfortunately this happens to most old equipment, and a lot of not so old equipment, especially if it uses printed circuit boards.