Instructables

How to fix a classic American AM tabletop tube radio

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Picture of How to fix a classic American AM tabletop tube radio
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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Step 1: Got radio?

Picture of Got 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.
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MarkS41 month ago

I recently restored my first AA5 radio, a GE model 101 made in 1948. Many thanks to KE4MCL for writing up this Instructable. It was quite a help. I replaced all the paper and electrolytic caps. I also had to replace the dial cord. I was surprised that I did not have to adjust the alignment any at all to pick up even the weakest stations in my area. Prior to this I have done very little with tube electronics, mostly chips and transistors.

This project turned out so well, I will try to bring a '50's Pilot AF-605 AM/FM mono only Hi-Fi tuner back to life next. That Pilot tuner looks clean under the chassis but I think I might have to replace quite a few more parts than on the GE. I am just starting research on the Pilot trying to find a schematic or service manual. Would anyone know where I can download either one? Thanks in Advance.

kong25502 months ago

thank you

bob303012 months ago
Wow, this is cool. I was born in 1960 so I remember tube TVs and Radios although transistor Radios seem to be more abundant when growing up (1970s). I do remember Drug, hardware and grocery stores having the station to check tubes and replacements for sale. You've now given me a bug to look for old tube radios to repair. Thank you for posting.
Wyle_E1 year ago
Memories... I'm of the last generation of techs who trained on tube equipment before we encountered transistors. At one time I had the standard AA5 schematics and all of the parts values and tube bases memorized. Repair shops used to have isolation transformers to make these radios less dangerous, but another solution was to measure the voltage between the chassis and an external ground. If the chassis was hot, reversing the power plug put the chassis on the neutral side of the line. Dial cord was just fishing line. Not monofilament, but nylon braid. Hardly anyone sells it as "dial cord" anymore, but fishermen still use it. Waxed dental floss will also work, but it's harder to tie. "Loctal" tubes have a glass envelope with a metal base that has a little bump on one side. Pushing on the bump, to move the tube sideways, releases the lock so you can pull the tube. This system was invented to keep tubes in aircraft electronics from vibrating loose, and it's pretty rare in AA5 sets.
mlmccauley1 year ago
Excellent explanation of a technical topic in a manner understandable by non-technical people. This is where we geeks almost always fall short.
i have a question i have a 59 zenith 7 tube radio when i turn it on it gets decent reception but it fades in and out after a while.....im using a pair of rabit ear antennas what could be my problem
I've got a tallboy radio with 9 tubes in it... would any of the instructions here be significantly different? Any chance of dangerous charge being stored in any of the capacitors?
ke4mcl (author)  gravityisweak1 year ago
It would be very similar. Still have all the same parts to replace. Your radio might have a power transformer in it thats all.

Leave it unplugged and switched on for a few hours and they will surely be discharged.
carchub2 years ago
Hello again! Just finished this step and got some tubes to in line to buy, except one. I can't find the number on it (by the way it's glass), and it looks like the inside is completely blacked out. I do see a sort of stamp on the top, but it's too worn-away, and all I can make out is a 19 and a 6. Oh, and a prong is missing on the bottom (there were two missing on another one, but I was able to get the number on that one). Thanks for your help, this is a really fun project, and I can't wait to set this thing up for listening!
ke4mcl (author)  carchub2 years ago
wipe the tube off so the glass is clean. go outside in the sun. give the area of the tube where you believe the numbers are, a nice slow exhale of hot balmy air from your mouth. this should cause condensation to form on the glass. while the condensation is there, try to catch some light reflecting off the area where you think the markings are. you may be able to read the markings off the tube as the condensation will appear slightly thinner on the areas that were marked thus giving you very faint but legible data.

this is an old radiomans trick
carchub ke4mcl2 years ago
Totally worked, and I got the number, 50L6! Thanks again
carchub2 years ago
How would you suggest removing the front knobs? My wont budge =( By the way thanks for this instructable, I just got myself a Magic Tone 500.
ke4mcl (author)  carchub2 years ago
some knobs had set screws that are visible on the edges. you will see a very small hole and if you look inside with some light you should be able to see either a hex or flat head screw. some military radios used 2 set screws per knob and they may be splined. you will need a bristol wrench set to remove those. most consumer radios though used a flathead.

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.
carchub ke4mcl2 years ago
Thanks so much! I can totally see the set screws on them =D
jjjjwiz3 years ago
Hello, I have an old philco that i just recapped. The radio will pick up all stations and sound good at low volume. When I turn it up - it gets lound but very distorted - any help would be great "I am very skilled in electronics and tubes, so get as technical as you like" THANKS
ke4mcl (author)  jjjjwiz3 years ago
check your speaker for cracks. these old speakers can also unglue from the metal frame causing buzzing when played loud.

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.
stienut3 years ago
Super ible. I can't wait to see what's up with my 1936 American Bosch. Very well done, indeed!
CBTman013 years ago
The lack of transformer was not for savings purposes, but to allow the radio sets to work on DC power lines, like those used in those days in many countries, including the US, in addition to AC power lines. Surprisingly, although there are virtually no DC power lines at the 115 or 208 voltages, many long distance transmission lines now carry DC, not AC, because it is cheaper (and feasible) to do so.

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.
ke4mcl (author)  CBTman013 years ago
i cant argue the dc aspect of your comment however the lack of power transformer is a different issue. it's widespread knowledge in many antique radio resources that the AA5 was born out of the desire to make radios more affordable when the depression hit in the 1930's. one of the most expensive single components in a radio was the power transformer. do away with it and you have a substantial cost savings. atwater kent chose to close his plant down instead of produce "cheap" sets when this issue became a big thing in the radio industry.
Great pic! Thanks! I never knew what a great invention the circuit board was. Some of my industrial controllers, still in use, from the 1980-90s have screen printed boards that look so quaint. Now I know... that quaint is great.
yeah,imagine a computer built like that...whew he ah ha! circuit board-less!
yea the whole thing would be as big as a refridgrater literally!!!
Ha yeah
I think you guys need to get to know ENIAC http://www.cs.dartmouth.edu/farid/teaching/cs4/summer.08/notes/historyofcomputing/eniac.jpg
jernlee4 years ago
Thank you very much for taking the time to help the people that do not know Thanks again jerry
Excellent instructable!  Very accurate, knowledgeable and, with only a couple of goofs, even spelled correctly.  I have a few old tubers here and am still waiting for the gumption to get off my *ss and fix them.  But I wonder about the cabinets.  I cannot find much about restoring that part.  Do you know any resources about fixing up wooden radio cabinets?

ke4mcl (author)  BasinStreetDesign4 years ago
i got nothing on woodwork. infact, im a lousy woodworker. i've saved a few wooden cabinets but im probably a 5 on a 1-10 scale at that aspect.
hey ke4mcl i just got a philco model 42-380. Fixed it and turned on speaker and on high it was not very loud ,any help?
ke4mcl (author)  fender-electric-guitar4 years ago
possible weak tubes. there are two tubes that are really the consumable ones and wear out faster than the others, the rectifier and the audio output. the audio tube usually wears quickest. look for the tube who's socket is wired to the output transformer for the speaker. on many radios its like a 25L6, 35L6, or 50L5 but theres other possibilities. if you look up the number of the suspect tube it will come back as a beam power tube or audio output tube.

they are usually cheap and can be found at antique electronic supply
ke4mcl (author)  fender-electric-guitar4 years ago
providing you have replaced all the old caps, the possibilities could be an out of spec resistor, an rf problem (circuitry that handles the radio signal), or a flat (worn out) output tube.

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.
hey not the tube checked it and not the best but works lots of static have to put hand on antenna by the way what is a speck resister? :(
ke4mcl (author)  fender-electric-guitar4 years ago
an out of spec resistor means that its actual value on an ohmeter is way off from what it should really be.

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.
thanks i'll check right now i'll let you now in a short time! :)
usarnie15 years ago
Good instructions! I recently redid a 1940 Canadian made Westinghouse, model 556A, All American Five tube radio that I purchased at an estate sale in California for $1.00. Since it was Canadian made, the schematic was not available on Nostalgia Air's web site. I obtained the correct schematic from a Canadian web site, www.JustRadios.com, for $7.00. The big difference between the Canadian AA5 Radio and an American made AA5 model of a similar type, is that the Canadian set used a 35L6 Audio tube and an 88 ohm, 2 watt, voltage dropping resistor, used in the filament string to drop an additional 13 volts, so the total voltage dropped on all the filaments nearly equalled the AC line voltage. The American made AA5 sets used a 50L6 audio tube without needing a voltage dropping filament resistor. Since the voltage dropping resistor on my Canadian made AA5 was previously destroyed, I decided to remove what was left of it and replace the 35L6 tube with a 50L6 tube that I purchased on ebay. I also decided to do some re-engineering to make this set operate safer. I removed the original 2-wire non-polarized rubber covered AC cord and plug and replaced it with a modern molded plastic covered 2-wire polarized AC cord and plug. I used my multi-meter, switched to continuity, to make sure that the neutral wire was connected to the chassis ground and not the hot wire! This eliminated the possibility of having a hot chassis and possibly receiving a shock! I also repositioned the on-off switch so it was now on the hot side of the AC input voltage instead of on the chassis ground side. My Canadian set uses a 6.3v pilot lamp connected in parallel with 1/2 of the rectifier's filament. As a safety precaution, so as to not burn out the 35Z5 rectifier tube's filament in the event the pilot lamp ever burnt out, I connected a 220 ohm, 1/4 watt, resistor in parallel with the pilot lamp's filament. Since current always flows through the path of least resistance, the pilot lamp did not loose any of its' brightness! I replaced all the paper covered capacitors and both of the electrolytic capacitors with modern ones. After I completed all the repairs and modifications, I plugged in the set and attempted to turn it on. Nothing happened! I unplugged the set and connected my multi-meter, switched to continuity, across the terminals of the AC plug, turned the on-off switch to on and I did not have any continuity! I determined that my 68 year old on-off switch was stuck in the open position, as I previously checked the filaments on each of the tubes and they were all good! I corrected the problem by spraying WD-40 into the cover of the on-off switch and worked the switch back and forth about a dozen times. Presto! Now I had continuity! I then plugged the set back into the AC outlet and turned the switch on. After about 15 to 20 seconds the radio came alive! It worked and I was able to tune in many radio stations. The only problem remaining was with a 56 ohm, one watt resistor, that was very hot to the touch. I replaced it with another resistor of the same ohm value and I increased the wattage of the new resistor to seven watts. The new resistor operated much cooler! While I was tuning and listening to the vintage radio, I found a radio station that played music from the 1940's. It was almost like going back in time!
desertdog5 years ago
Excellent and informative. I can now feel more confident about purchasing a used radio knowing that it may be repaired. I also liked the "natural selection" comment. Whatever happened to personal responsibility.
If you find a model number for the radio, do a search online for it. You might find schematics, parts info, parts, tuning info, etc. An example of such sites is http://oldtech.net/RCA.html
tundrawolf5 years ago
Hello, I have a couple of old tube radios and tube guitar amplifiers (All vintage). They all work very well, and all the capacitors look good (original) and don't leak. Do I have to replace them? There's an awful lot of them.
nickbuls5 years ago
tube radios are soo cool. they look and sound better then transistor radios. I'm now building one at home. It has a ECF80 tube with a triode and pentode in one tube.
radio1.png
I would appreciate if you would tell me how you were able to add a schematic to your reply on this post.
just copy the picture and paste it in the reply box
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