How to fix a classic American AM tabletop tube radio

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.

Dear Sir: I would be grateful if you or any kind person could help me fix my old GRUNDIG RADIO MODEL 4670 U/STEREO AM 7 CIRCUITS, FM 10 CIRCUITS of Germany. The radio was in running condition for AM. But the FM transmission would stop after a minute or two. One mechanic tried to fix it, but the radio is now working at all. The magic eye is not on, no sound. I thought the magic eye tube was damaged. So I procured a magic eye tube and replaced the old one, but no remedy. I will be grateful if someone could help me. I am in Bangladesh. I would be traveling to USA on May 8. I wonder whether I can get any help in USA. But I cannot carry the radio all the way to USA. I can send photograph of the radio and the model numbers of different tubes. Please also send a copy of your message to my personal address: Sincerely, Maswood Alam Khan

ke4mcl (author)  maswoodalamkhanyesterday
it sounds as if your technician may have done something to disconect or disable the power supply, in which case the whole radio will be dead as you describe. the magic eye tube is expensive and rarely goes bad unless physically damaged (break in glass).

i would suggest you open an account on and try to locate a schematic there. the schematic is the electrical diagram. you can definitely get a schematic via radiomusuem but joining cost money and the process is slow.

once you have a schematic, any good electronics tech that has some experience with older electronics should be able to save it. those radios used a selenium rectifier that is encased in a flat aluminum rectangle about the size of a thick playing card. that part and the power supply capacitors should be replaced. the rectifier fails and destroys the capacitors.

Thank you, sir, for your response. The power supply is there as the dial lamp is on, and the tubes are also glowing as usual. But there is no sound. In Bangladesh it is impossible to find tubes or other parts of the old radio. I am thinking of taking notes and images of all the parts and tubes of the radio. Or, if you suggest, I can bring the chassis to USA to replace the parts as I am coming to Maryland, USA on May 08. I would be grateful if I could get your contact numbers and email address. Thanks again. Maswood A Khan (

JakeL61 month ago

Thank you. The article was informative and very helpfiul. I was specifically looking for info on the electrodynamic speaker and got it.

glennby6 months ago

Hi, I'm needing a little help. i have this 1962 Silver-tone console stereo. i'm having issues with am/fm it'll receive am with a lot of static and tune to one station. fm will not work at all. i have antenna hooked up. This is a tubed console the record player works great. can any one of you folks point me to the tube or area for t/s. thank you!.


glennby glennby5 months ago

Thanks for the input, what type of equipment do i need?.

Thanks again.


ke4mcl (author)  glennby5 months ago
you would need a copy of the Sam's Photofacts for your model, a stable RF signal generator that can go all the way up to the FM broadcast band, a set of RF tuning screwdrivers, and a decent VOM.
glennby ke4mcl5 months ago

Hi and thank you for the info. i've purchased a signal generator and will be here shortly. from a person who had it since new. has the instruction book with it as well. i'm still buying some tools, i would like to do this as a hobby, i love vintage HiFi's. i'll be retiring shortly and want something to do. i see that your a Ham, so am I. my call is WD4HVY. 73's again thanks for the info.

ke4mcl (author)  glennby5 months ago
this sounds like an RF issue which unfortunately may require special test gear.
MarkS48 months 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.

ke4mcl (author)  MarkS45 months ago
btw... when working on any tuner its EXTREMELY important that you install all replacement parts in the same position as the old ones. all leads should be in the same exact place. this greatly lessens the need to realign the tuner when you're done.
ke4mcl (author)  MarkS45 months ago
i rebuilt one of those. didnt need the schem. not much different than working on AA5's.
kong25509 months ago

thank you

bob30301 year 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 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!
CBTman014 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)  CBTman014 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
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)  BasinStreetDesign5 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-guitar5 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-guitar5 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-guitar5 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,, 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
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.
nickbuls6 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.
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
Hi ke4mcl, I have a tube radio at home.I am not sure what time period it is from(I think 1940's-50's).All I know is that it is a German Hornyphon radio. You access the chases from the bottom of the cabinet when you unscrew the two screws. It has five trioiron radio tubes two have EF89 the rest are all different EZ80,EL84 and EM84. Also one that is from different place I can't read the words all gone other then ECH81.IThe radio has four Frequencies lw,mw,swI and swII.One suggestion take the radio tubes out so you don't bump or break them.Also my radio is on this site search for Tube the title will be Tube Radio by icoaster. Bye P.S.I gave you five out of five:)
w8znx6 years ago
well done dit dit
tinkernaut6 years ago
Great i'ble!!!! I've had this old Philco I picked up on ebay for a couple of bucks. Now maybe I can get to actually fix it!! Here's an idea: Build a low-power AM transmitter and connect it to an MP3 player playing old time radio shows. Then listen to them on your restored tube radio. Nothing like the ambiance of tubes glowing while listening to Suspense with the lights out. :-)
perlpower6 years ago
Something I would personally recommend is instead of plugging it strait in after doing the replacing is to plug it it though a variac to slowly warm up the tubes.
Coati6 years ago
Very nicely done,I have an old Motorola five tube that I like to turn on in the evening while eating dinner.The glow of the tubes and the usual lack of top 40 music on the AM band makes me feel like I am in a different era.Thanks for the info.
Just found this site! Very well done. I can't wait to tear down my old radio and see what happens.
jomaro6 years ago
Gee... thanks! I just happen to have one of those in the garage waiting to get fixed! I just didn't know where to start. I do a bit of digital electronics but I feel I'm to far away from "super heterodine" stuff. I'll put another comment and photos when I will get working! Great 'ible!
canerods6 years ago
You covered the process very well. Easy to read and understand. Thanks very much! You may want to add this tip in future: Since speaker cones are very fragile. One way to keep from damaging the paper cone while your working on the radio is to cut a thin cardboard shield and tape it to front of the speaker to protect it. Be sure your tape only contacts the metal frame and your cardboard shield -- not the speaker cone material itself.
ke4mcl (author)  canerods6 years ago
good tip! added to the instructable
Cool! Great Instructable!
bustedit6 years ago
Thank you, great ible. I inherited a Grundig from my grandmother, and it has a lot of memories for me. It is actually an AM/FM/LW/SW, and when we would visit, at night my cousins and I would tune in europe and bath in the glow of the lamp and the gentle hum! it has a small cool blue lamp for reading signal strength, two lines that meet together for a stronger signal. How much different would this be than an AA5, other than mode selection? jeez, it even has a sort of EQ - talk, jazz, and orchestra maybe? Smells great, too.
ke4mcl (author)  bustedit6 years ago
its more complicated but has alot in common. you actually have a real power supply and more tubes. the main thing to worry about is the big electrolytics in the power supply. im not sure if they used paper caps in those radios. those radios sounded real good and are worth fixing up. some used electrostatic tweeters which are considered audiophile stuff nowdays.
bustedit ke4mcl6 years ago
so my loss of life is less of a factor if i stick my wet finger in there, as long as i dont discharge a cap? the reception on that set is amazing - at night I get quite distant FM and even further AM. I live in Mass and I hear southern states. The music selection, usually talk radio, plus the sound of the radio feels like I'm stepping back in time. Thank you for the tips.
Calorie6 years ago
Neat description. However, it leaves me more scared of tube stuff than before :-)
ke4mcl (author)  Calorie6 years ago
not all tube radios were built this way. the better ones used an actual power supply and dont have the dangers of the AA5. theres still high voltage inside though.
ke4mcl (author)  wierd idiot6 years ago
why not? its a relic from when we made just about everything in this country. when radios cost a weeks pay and were built to last many many years instead of disposeable.
gmoon6 years ago
Nice job. Only one nit-pick. The field-coil of an electrodynamic speaker is (like the dial lamp you mention) also an integral part of the circuit, and does double-duty. The field coil not only magnetizes the speaker, it almost always serves as a choke for the power supply. Replacing an old blown field-coil speaker with a modern permanent magnet speaker requires additional modification. You certainly didn't advocate replacing one type with another...but maybe a warning that they aren't interchangeable?
ke4mcl (author)  gmoon6 years ago
i'll clarify that in the instructable.
carpespasm6 years ago
Very cool instructable. I've always wondered some about those old tube radios. I grew up taking apart old (to me at least) solid state boom boxes and stereos. Still quite the learning experience with turn tables that had melted belts and stuffing a head unit into a speaker box sans 8 track and turn table guts to make some room on my dresser.
gmoon6 years ago
Added this to the "Vacuum Tube" group...
Great 'ible! I have restored many old radios and you've summed up the process quite well.

I would suggest checking resistors while you're going about replacing capacitors. The resistors used in those old sets tend to drift upward in value as time passes and this will affect bias voltages on tubes.

It should also be mentioned that service data for these old sets were published by two companies- Beitman and Rider. Their multivolume radio service manuals can be found in many public libraries. The manual pages usually have full schematics, tube pin voltage levels, and tune-up instructions. Scans of Rider's manuals are found on-line here:
If you want your own original set of the manuals or DVDs full of scans you can check ebay.
brainwise6 years ago
I loved this 'ible.
Phil B6 years ago
Very well done! You covered a lot of things in a little space and did a complete job of it. Modern transistor radios are virtually trouble free and give very good sound, but, if you grew up with top 40 hit lists during the 50's and 60's, there is nothing like an old tube radio. About 20 years ago someone gave me two old tube radios and I got one of them working. Something is missing from listening to top 40 hits if the original cracks, flutters, and wows are not there. You get those only with a tube radio.
shooby6 years ago
Richard Feynman style. Great 'ible