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Back in the day somebody always knew somebody else that could fix minor things on radios and that's what I'm going to cover here. In this instructable I'm going to walk you through the basics of getting an old tube table top radio up and running. Finding a repair shop that can fix old radios can be real tough. If you do find one, the bill may be pretty daunting. This will not cover 100% of all problems but will get most radios that aren't severely damaged back in operating order. This instructable assumes that you have some electronics background, you can read values on parts, and you can solder. This instructable is geared towards getting a common 5 tube AM table top radio working but the info presented is applicable to a multitude of old tube radios.
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Signing UpStep 1Got radio?
So you just inherited a cool old radio from grandma, or perhaps you saw this neat looking old radio at a yard sale and couldn't resist the price. You lug that wonderful behemoth of American craftsmanship home and get ready to plug it in... STOP! DONT EVEN THINK ABOUT PLUGGING IT IN!
Plugging in an old vacuum tube radio thats been sitting for years will usually result in bad times. You might let out the magic smoke (burnt component), damage tubes, short stuff out, trip your house breaker, or maybe even catch fire. Think I'm kidding? Read on and I'll walk you through a little radio history and some electronics lessons.
Plugging in an old vacuum tube radio thats been sitting for years will usually result in bad times. You might let out the magic smoke (burnt component), damage tubes, short stuff out, trip your house breaker, or maybe even catch fire. Think I'm kidding? Read on and I'll walk you through a little radio history and some electronics lessons.
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this is an old radiomans trick
if your radio doesn't have set screws and the knobs wont budge your going to have to turn the radio so the knobs are facing down. take a can of wd40 and use the straw to get a shot of wd40 onto the knob shaft. let it sit a while. it should break free.
if the speaker is ok, my next target would be the output tube. its consumable and does wear out. the good thing is that most output tubes on table radios are not expensive. there's plenty of types of output tubes used but google is your friend here. google search each tube number. the one that comes back as "audio amp tube" or "beam power tube" or "audio output tube" or something along those lines may be your culprit. you can usually find radio audio tubes as New Old Stock on ebay for just a few bucks.
If the voltage of the filaments did not add up to 120 or 220 V (used outside the US), the manufacturers added a resistor for extra voltage drop. In many cases, to save space and reduce internal heat, such resistor was wound inside the power cord, which made it warm to the touch when the radio was on.
The safest way to work with a "Five" is to use an isolation transformer (1:1) of the right volt amp rate (around 200 VA). This way, none of the power cord wires would be related to ground and it would be possible to touch the chassis without a 50/50 chance of getting electrocuted.
they are usually cheap and can be found at antique electronic supply
turn radio on in a dark room and keep an eye on the tubes. if the large metal cylindrical structure in the tube slowly begins to glow orange after maybe 5-10 minutes of use you may have an out of spec resistor. keep in mind im not referring to the filaments of the tube, those are supposed to glow.
make sure your antenna is ok. a broken antenna loop will cause lousy reception.
a worn out output tube will cause low audio. listen closely to the radio. if it sounds good at low volume but just wont play very loud before distorting, you may have a worn out tube. most small radios used 25L6, 35L6, or 50L6 output tubes.
get back to me here and let me know what you find.
you mentioned that when you put your hand on the antenna you get lots of static. many old radios used loop antennas. the antenna has at least two wires, sometimes 3 or 4. whatever wires it has they must be hooked up, if not the radio will pick up lots of random noise at stations will be drowned out.
you can check the loop antenna by disconnecting it and measuring continuity with a meter. its rare but sometimes rough handling causes one of the wires to break in the loop.