As a kid in Virginia (a state in the United States), I remember my father had a Novice Amateur Radio License (Update: His callsign was KN4JRF. Now I have it).
Back then, in the 1950's, a person (usually a veteran from World War 2, using the glut of relatively inexpensive equipment sold after the war, and military surplus ham-adaptable gear available then) could get a ham license, and, as long as they upgraded to Technician Class or higher within one year, they could keep it.
The means of amateur radio communications widely employed at that time was CW (Continuous Wave or Morse Code), but there was also lots of AM stuff to listen to on the "Short Wave" bands. And this was way before "transceivers", ham radios that could receive on a receiver, then transmit on a separate transmitter .
Dad never progressed past the Novice license, but the memory of that 1 year, with his QSL cards (distinctive postcards acknowledging contacts with distant ham stations) stuck on the side of the boiler in the basement, the Hallicrafters S-38A receiver, the Globe Scout transmitter and the CW key screwed to the desktop, still sticks with me today.
(Now, this is coming from somebody who remembers party line telephone networks, pay phones where a local call was 10 cents, rotary dials, 6 volt automobiles, farm tractors where the driver sat in the open, under the blazing sun, and drifting snow, no air conditioners, no color TV, no GPS or internet.)
Yeah, that's what they call the "good old days" (hell, the smartphone I have in my pocket is about a million times smarter than the stuff they trained me on in the USAF).
When I volunteered for the USAF in '68, they guaranteed me a job in the field of electronics. And after the mandatory basic training, I was sent to Chanute AFB, IL to study electronics (it was so damned windy and COLD then, I swore I'd never come back to Illinois again), to be followed by bombing and navigation trainer training for 9 months. After that, I got sent to Nellis AFB (Las Vegas), Nevada until August 1972.
During all that training, Uncle Sam attempted to teach me electronics, half of which was in the form of vacuum tubes, which were still in common use then.
(Because tubes operated by heating up a "cathode", which caused the electrons in get loose and start flowing - which is why it's called "ELECTRONics" - we were taught "electron flow". Later we were told to forget all that, because it actually flowed the other direction, which was called "conventional" flow, or "hole flow". I figured that's one of the reasons I'm so confused.)
And then from 1972 to 2015, I forgot most of it what I learned. Life got in the way.
But I got my ham license in 1993, and stayed with the hobby, trying to remember all the stuff I forgot.
Finally, at a hamfest, I stumbled on someone who was attempting to sell some old tube-type receivers (Hallicrafters S-38B and C) like the one Dad had when I was a kid (he had an S-38A). I offered the man $25 for one. He said for $25 I could have both of the ones he had.
Thanks to my ham license (and a BIG thanks to the resources available on the Internet), my refresher education was just starting (and some in ham radio said that the Internet was killing ham radio. Yeah, sure!).
Check out these links if you're into restoring old radios, or electronics in general:
So there I was, the new owner of a receiver manufactured in the late 1940's. Luckily for me, I did some reading before attempting to plug it in.
For a variety of reasons, the old radios that one would find "nostalgic" weren't ones that you could take home, plug in and expect to work.
Also I found out that the radios I knew as a kid are now known as "killers", because they were designed so that the chassis MAY have full wall AC voltage on it.
At the time there wasn't much concern about polarity and grounding, and the chassis was electrically isolated from the outside world just fine, as long as one didn't open the case.
But as the years went by, the rubber grommets keeping the chassis and the metal cabinet separated deteriorated, causing the potentially "hot" chassis to possibly come into contact with the cabinet, and the unsuspecting user.
Also the paper capacitors that were used at that time may have broken down and become "leaky". The term "leaky capacitor" means that it no longer functions as a capacitor should. A good capacitor passes AC and blocks DC. A leaky one passes DC or low frequency AC. Which causes hum and may damage or destroy vacuum tubes.
By the way, in my obsession to restore old radios, I got a Hallicrafters S-53A recently at a hamfest. The first thing I did when I got it home was measure the resistance from both prongs of the power cord to the chassis, WITH THE POWER SWITCH ON (very important)!
Even though this radio has an isolation transformer (a transformer that isolates the chassis from the grounded neutral), it still had AC voltage on the chassis. Back when this radio was built, there was a standard paper/wax capacitor between AC and ground. The purpose was to bypass any weird stuff floating on the AC line to ground. The "safety capacitor" wasn't invented yet. Now we have AC line voltage which is generally higher and has lots more weird stuff on it, so safety capacitors were introduced and they are required for device certification. For more information on safety capacitors, go to
www.justradios.com's discussion
here.
Update: Even though the 53A has an isolation power transformer, there was still AC voltage on the chassis. Turns out there is a .01uf capacitor that is connected before the on/off switch, intended to filter out any noise and other "garbage" from the 110VAC (now 120+VAC) input. At 60 Hz there was supposed to be 265 kohms capacitive reactance. The capacitor is rated at 600 volts. What could go wrong, huh?
But the original wax/paper caps start failing after they get a few decades old. A survey of most YouTube sites dealing with old electronic equipment HIGHLY recommend replacing old paper capacitors with new ones. This capacitor at the input of the power transformer was originally intended to pass RF AC and block the 60 cycle AC. This capacitor is referred to as the "death" capacitor, and was commonly used on old radios and amplifiers (including guitar and P.A. amps... hint hint hamfest folks). There are many stories of people getting shocked off the guitar strings or mics. Remember that next time you fire up that "boat anchor".
Once I brought home the S-53A, I removed all of the paper caps. Then I tested them with the inexpensive tester described below. The results are shown below:
If there's any doubt as of the accuracy of old capacitors in old radios, and the wisdom of assuming they'll work in the circuit, see the following table:
| Old (Nominal) | Old (Measured) | +/- 20% tolerance | New (Nominal) | New (Measured) |
| .01 uF “Safety”(600V) | .0274 uF OT | .008 – 012 uF | .01 uF Safety X1/Y2 (250V) | .01033 uF |
| .01 uF | .0272 uF OT | .008 – 012 uF | .01 uF | .01004 uF |
| .01 uF | .0148 uF OT | .008 – 012 uF | .01 uF | .009834 uF |
| .01 uF | .016 uF OT | .008 – 012 uF | .01 uF | .009937 uF |
| .01 uF | .0281 uF OT | .008 – 012 uF | .01 uF | .0128 uF |
| .1 uF | .562 uF OT! | .08 - .12 uF | .1 uF | .1072 uF |
| .05 uF | .057 uF | .04 - ,06 uF | .05 uF | .0475 uF |
| .05 uF | No value OT! | ? | .05 uF | .0506 uF |
| .02 uF | .059 uF OT! | .016 - .024 uF | .02 uF | .0202 uF |
| .02 uF | .027 uF OT | .016 - .024 uF | .02 uF | .01991 uF |
| .02 uF | .038 uF OT | .016 - .024 uF | .02 uF | .01933 uF |
| 50uF Electrolytic | 84.6 uF OT! | 40 – 60 uF | 47 uF Electrolytic | 46.5 uF |
| 10uF Electrolytic | 21.4 uF OT! | 8 – 12 uF | 10 uF Electrolytic | 11.07 uF |
| 10uF Electrolytic | 25 pF (25uuF) OT! | 8 – 12 uF | 10 uF Electrolytic | 10.18 uF |
| 10uF Electrolytic | 21.6 uF OT! | 8 – 12 uF | 10 uF Electrolytic | 10.40 uF |
| | | | |
OT = Out of tolerance. OT! = WAY out of toleranceAs you can see, even disregarding DC leakage concerns, and assuming any capacitor measuring within 20% of its marked value is within tolerance, 14 of the tested 15 capacitors were out of tolerance. In fact, 7 were
EXTREMELY out of tolerance.
“Nominal” in the above table means the value printed on the component.
Another of the possible measurements, and this is critical, is the voltage rating of the capacitors in an old radio. An old paper or electrolytic filter capacitor (which is usually also made with paper) can still read good, capacity-wise, but be "leaky", in that it passes voltage lower than its rated breakdown voltage.
Why? Because I can’t justify spending a lot of money on stuff, that’s why (Also it comes in a kit. And I love kits).
In spite of its being called a "Transistor Tester", it also tests capacitors, inductors, resistors, etc.
It’s good enough for me.
Please note the “nominal” values (or the values that are marked on the old capacitors) vs the measured values. For example, the existing old one marked ".1uF" actually measured 0.562uf.
And one could argue that inexpensive measuring equipment could give erroneous values, thereby making assumptions invalid. However, the new capacitors were measured with the same inexpensive “Transistor Tester”. In other words, the new one marked ".1uF" measured .1072uF. Pretty close for a cheap tester, I think.
My conclusion was that if the old cap reads more than 20% off the rated value, change it out for a new one. No need to waste time or money building any other test equipment to help you make a decision. Just change it out. Like running an oil analysis on an engine that's 10K miles overdue for an oil change. Why go to the trouble and extra expense. Just change it.
Update 2/11/2022: Also, I gotta stress that ALL capacitors have to be discharged before testing. Capacitors are similar to batteries, in that they hold a charge. It may be big enough to hurt you, or scare you into jumping back into another dangerous voltage in the radio you're working on, or, most likely, shoot a brief voltage charge into the delicate piece of test equipment you're working with, or destroy it.
The "Shell" (the enclosure. It's very handy. It needs to be part of the device. Many kits made in China don't include an enclosure) in the link above has a warning on the front saying that "Allways be shure to discharge capacitors before connecting them to the Tester!..." (It's not a typo. That's the way it's spelled.)
Ok, their spelling leaves much to be desired (how 'bout those Americans who misspell "your" when they mean "you're". Or "whose" when they meant "who's". Anyway, their English is way better than my Chinese). And the English text is buried beneath the Chinese text. And the "Warning" could have been printed better so as to catch your eye. Well, welcome to the new normal.
They're serious about this stuff. Take it from somebody who's been there. I've blown several expensive fuses in my DMM that also checks capacitors because of doing this.
