Posted October 24, 2001
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The Hallicrafters S-38C is a basic receiver, which tunes from 540 kHz to 32 MHz, either AM or CW (Morse code). The S-38 series was introduced in 1946, right after the end of World War II, and was definitely intended to be a cheap entry-level radio for a populace suddenly hungry for news. You can find far better-researched information about the S-38 series by searching the web than I can present you.
I picked up the above pictured rig at a Seattle area hamfest a few weeks ago for $20. When I asked the seller if it worked, he vaguely said, "I plugged it in a few months ago, and it powered up, but something wasn't working right, I can't remember what..." I talked him down to $20 and agreed to buy it, since I find myself with a growing interest in tube radios, and heck, it was only $20.
When I got the radio home, sure enough, it didn't work at all (as I had suspected might be the case). The main tuning dial cord was missing, so the main tuning couldn't be operated. The power cord was cracked and scary looking, and when I peered inside, I discovered that someone had cut off a previous power cord at about 1 inch from the solder points, and twisted/electrical taped the current power cord in place (no solder). Certainly scary enough.
So, I ran out to the fabric store and picked up some button thread, which is a cotton-covered nylon thread and plenty strong enough to operate the dial, and acquired a bare-end power cord at the hardware store. Unfortunately, those fixes were not enough to get the radio working.
A good deal of poking around later, and I determined that the power rectifier tube was dead (broken heater filament), and possibly other tubes were dead as well. I ordered a new set from ESRC, which arrived in decent shape, and apparently functional, for a fine price.
The new tubes went into the radio, along with a new set of metal-film capacitors to replace the old wax-impregnated paper capacitors. That should have taken care of all the problems, but there remains a great deal of noise whenever a strong signal isn't present. It sounds like AC hum, but not a pure sine wave signal, more like a rushing buzz. My guess is that it's either the RF or AF stage oscillating, but I'm not sure how to fix it. Check back to see what it turns out to be. Email me if you have an idea what the problem is.
It's not the AVC circuit, which I had thought it might be. I found this excellent site on troubleshooting superheterodyne receivers (excellent except for the stupid GeoCities pop-under ads), which has helped a fair amount.
It looks like the noise is probably coming from a previous stage, earlier in the conversion process than the AVC.
Further update, Nov. 16, 2002...
I finally got the radio working, more than a year after buying it. It eventually turned out to be that the adjustable inductors called "A2" and "A4" had to be adjusted to eliminate the resonance that was occurring. I'm listening to the radio even now, on some as-yet unidentified news program near 10 MHz. Woo!
Created by Ian Johnston. Questions? Please mail me.