Introduction: 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.

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.

Step 2: The AA5

Picture of The AA5

Sometime in the 1930's, somebody figured out that you could build a radio without a power transformer. Power transformers are expensive, maybe the most expensive single part in the radio. Do away with it and you save a bit of cash. This design became known as the All American Five. No transformer and five tubes. The voltage of the filaments all added up to about 120v. We'll refer to it as the AA5 from here on out.

The AA5 design was produced by the millions in many different incarnations using a variety of tubes. As new tube designs appeared, they made their way in to the AA5 design. You can find AA5 radios that use both 1930's designed tubes and 50's era miniature tubes on the same chassis! Despite the different tubes they used, they all follow a very similar circuit design and are an easy radio to learn to work on. There are derivatives of the AA5 that used more or less tubes but they all had the same thing in common, no power transformer.

Before cracking into that antique radio, we need to stress a few words of caution. An AA5 radio can kill you if you're not careful.

How can a radio kill you? Back to the history lesson! The AA5 radio and its derivatives use no power transformer. To pull this off one side of the line cord was connected right to the chassis. Keep in mind this was back in the day when natural selection was more the responsibility of the user and not the manufacturer. It's very important to not try to work on this radio while its plugged in. You also need be very careful not to touch any metal parts or exposed screws on the radio when its plugged in as they can be energized at line voltage potential.

Ready to dig in? Let's go!

Step 3: Remove the Chassis

Picture of Remove the Chassis

First we need to get the chassis (old time radio lingo for the metal frame that held all the electronics) out of the cabinet. This usually involves removing a back cover if there is one, removing the knobs, and removing the mounting screws under the radio. When removing the screws under the radio be careful when you loosen the last screw as the chassis could fall right out of the radio. Once all the mounting screws are removed the chassis should easily slide out. If it doesn't come out, check for mounting screws inside holding the dial area to the cabinet.

Once the chassis is out you may want to take some cardboard and cut out a circle that fits over the speaker. Carefully tape the cardboard over the speaker. You want the tape to stick to the metal speaker frame and not the cone or the cardboard edge of the speaker. This is going to protect the speaker cone from damage while you work on the radio. Once you become experienced in working on these old radios you might skip this step but if your clumsy, have a crowded workbench, or just want to play it safe, it's worth the effort to protect the speaker!

Step 4: What Is It?

Picture of What Is It?

Ok, radio is out. What am I looking at?
On the top side you should see the dial mechanism, the speaker, RF transformer cans, maybe a speaker transformer, tubes, maybe some filter capacitors, a dial lamp or two. Underneath the chassis you should see a myriad of capacitors, resistors, and other parts that may seem odd. Don't unplug or remove anything.

Step 5: Inventory the Tubes

Picture of Inventory the Tubes

Here's our first step in getting this radio up and running. Get a sheet of paper and writing utensil handy. Make a sketch of the top of the radio chassis as it looks from overhead. This is going to help you keep track of the correct placement of the tubes. Once the sketch is done and you've marked where the tubes are its time to ID the tubes and jot the info down in its corresponding spot on the sketch. You might get lucky and find that the radio already has such a diagram inside or underneath. Make a new one anyways as sometimes the old labels are brittle and come off easily.

One by one you are going to pull the tubes out and jot down their part number. Its very important that you do this one by one and don't loose track of where they go or mix them up. They are not interchangeable from socket to socket even if they fit!

To remove a tube grab onto it with your hand and give it a very gentle rocking motion as you pull on it. For very stubborn tubes such as LOKTALS you may have to carefully use a flathead screwdriver to pry the tube free of its socket. Be careful doing this so you don't damage the tube or the socket.

Once you pulled the first tube out look for its part number. The part number will consist of a number or numbers, a letter or letters, and a number all grouped together. An example of a tube part number can be 50L6, 12SK7, 35Z5, or 7C7. Write down the tube number in its respective place on your sketch.

While you have the tube in your hand, lets look for obvious signs of tube failure. Tubes can be glass, metal, or both. If they have a glass top it may have a silver mirror like spot on it. This is normal. If the tube has a white haze inside, its cracked and lost its vacuum. It's bad. Obviously this check is only good on glass tubes. Next visual check is to look for loose stuff inside the tube. Any loose stuff inside the glass is bad. Once again you cant see inside the metal envelope tubes so you may have to result to shaking them and listening attentively for any little rattles. Don't tap as this will make the insides of the tube rattle and cause a mis-diagnosis.

The above method will help find blatantly bad tubes but it wont help much with worn out tubes. You need a tube tester to perform proper tests on a tube. The good news is tubes are more rugged than people sometimes make them out to be. Even with worn out tubes your radio will still play, just not as loud.

Got a known bad tube? An amateur radio fleamarket or the web are good places to find replacements.

Once all the tubes are out inspect the sockets for cracks or burn marks. A cracked tube socket will more than likely need to replaced. A burnt/overheated one will definitely need replacing and that's beyond the scope of this instructable.

Step 6: Wax and Paper

Picture of Wax and Paper

Next step, turn it over!
Find a way to support your radio while its upside down so as not to stress or damage any parts and lets dig in!

Underneath you'll find a multitude of obsolete parts. Some are easy to read, some are not. First we'll worry about looking for physical damage. We're looking for burnt or overheated parts. Charred stuff is bad. If you find any charred parts its pretty much game over. You'll need to get a schematic for your radio to figure out what burned. A good source for free radio schematics on the web is nostalgia air.

Look Ma! No circuit board!
Most tube radios where built by hand and used point to point wiring.

While you are in there do not poke and prod. Old wiring becomes brittle. Unnecessary poking and prodding will result in unnecessary loss of insulation resulting in necessary replacing of more stuff! some of the rubber they used back then survived just fine, some got very brittle. The good thing is that if you don't move it, it wont flake off and the wire will retain the shape it has taken. If you feel uncomfortable with the brittle stuff you can replace it but be very careful to route things back where they were and connect them back to the same exact spots. You'll need a good soldering iron for this. Little 15 watt irons wont work.

While on the topic of wiring, lets talk about power cords. If the power cord is brittle, dry rotted, or is cloth, replace it with a new 2 wire cord. When you remove the old cord strip some of it and make sure it's a plain old copper lamp cord. If it looks like some kind of spiral wound silver colored stuff it may be resistance cord. Resistance cord was used in early AA5's to drop some of the voltage feeding the radio. The stuff is hard to get. There are workarounds but they are beyond the scope of this instructable. Doing away with the resistance cord and just wiring in regular cord will result in a very short lifespan for your tubes!

Back to working under the chassis!
If your radio is mostly or all original the first thing that may stand out as that don't look right are the wax paper capacitors. They get a dusty, dirty look to them and sometimes blow their innards out the ends. All wax capacitors should be replaced regardless of how new they look. If they haven't already, they will fail. Wax capacitors look like little paper cylinders that have been dipped in wax. They are usually rated somewhere between 0.001 and 0.7 mfd (micro farad) and have a voltage rating of several hundred volts. These must ALL be replaced. They are what is commonly used to couple the different section of the radios circuitry together.

Along with the wax caps, the next item that must be replaced is the electrolytic filter cap or caps. Here you are looking for a large cylinder that can be made of metal or metal encased in cardboard. The value will usually be somewhere around 20-50mfd at 150 or more volts. These are very important as they are what filters the DC voltage that runs the radio. Bad filter caps will result in loud hum or even damage to the radio.

Back to the note pad!
Get your notepad out and make an inventory of all the wax and electrolytic caps you will need to get. Write down the values (mfd and voltages). While reading the caps be very careful to cause as little disturbance to adjacent components as possible. Any wire you move may lose its insulation. A set of long nose thin needle nose pliers are excellent for this task. Feel free to grab the body of the capacitor and carefully turn it to facilitate reading its values. If the wax is too dirty to read the value on the cap just use a small flathead screwdriver to scrape away the exposed wax layer. I strongly advise against cutting out caps in order to read them. One can very easily forget where they went and end up causing more damage.

Step 7: More Caps

Picture of More Caps

Other caps in the radio.
There are other types of capacitors in the radio. There may be plastic encased paper, plastic encased mica, ceramic disc, variable air, variable mica and ceramic tubular. The plastic encased paper caps should be replaced per several sources I have read but I have never had a need to. The issue with those types is that the markings on the caps may be non standard and even if they are the standardized color dot system, they changed over the years. I own several radios that play just fine with their molded plastic paper caps still in them. If you have your heart set on replacing every single cap in the radio I suggest you obtain a schematic for the radio and also a vintage RETMA capacitor color code chart. Allied radio put out a radio data book in the 50's and 60's that had those charts in them. They are an easily found book at amateur radio fleamarkets and online auctions.

A list of some of the different color code charts can be found here..

Where to get the capacitors?
If you're not lucky enough to know someone that has a well supplied junk box then your best bet is Digikey, Jameco or Mouser. You're not going to find paper caps. There are plastic, mylar and mica replacements. High voltage electrolytics like what's used in the filter caps for the radio can be scrounged from old CRT monitors. Try to match the capacitance value as exactly as possible but don't settle for less than what was in the radio originally. The voltage spec can be a little higher than what the radio had but never lower. Using a cap that is underrated voltage wise will result in a bang and a foul odor!

The easiest way I have found to replace old caps is to snip out the one I'm working on leaving as much of the original leads in the radio as possible. I then take fine point needle nose pliers and make a tiny loop in the old lead. I take the replacement part, cut the leads to the size I need and slip the leaps into the loops then solder in place. Always double check after every cap you replace to make sure that you haven't inadvertently moved anything out of its place and caused a short.

Replacing the filter cap.
Polarity (orientation of + and -) is extremely important here. Its not important on the small coupling capacitors but on the filter caps it is. Read the old cap before removing it and note the polarity of the wires. Failure to observe correct polarity on electrolytics may result in exploding capacitors and bad odors emanating from your work bench!

Due to its size, the filter cap was sometimes fastened in place. The modern replacement may be half the original size or smaller. You may need to attach the replacement filter caps inside the radio to keep them from flopping around and shorting things out. I have found zip ties, rtv silicone, and 5 minute epoxy all to be worthy candidates for the task.

Ok, at this point we have replaced the wax paper caps, replaced the electrolytic caps, physically checked our tubes and sockets, and replaced our power cord if needed.

Step 8: Lamps, Switches and Sockets

Picture of Lamps, Switches and Sockets

Next stop the dial lamp!
What's so important about a dial lamp? You'd be surprised!
The dial lamp on AA5 radios was actually figured into the voltage drop of the filaments when they designed the radios. When you turn on a properly working AA5 radio you'll see the dial lamp go really brite for a short second, then dim, then slowly back to brite. If the dial lamp is missing or burnt out, it will shorten the life of the tubes. Type 47 bulbs were commonly used as dial lamps on AA5 radios but double check yours before replacing it. The bulb number may be stamped into the base of the bulb.

On to the switch and sockets!
Now would be a good time to spray your volume control with contact cleaner and work it back and forth a few times. You may see a little hole around where the leads enter the pot. Thats a good spot to get a shot of cleaner in. Spraying the tube sockets might be a good idea also. There are mixed feelings here on what to use. I personally use WD40 instead of contact cleaner on all my scratchy pots and tube sockets. Some purists cringe at the thought but I have never had a problem with it. WD40 is easily available and costs much less. When spraying the tube sockets take the tube and work them in and out of the sockets a few times to loosen up any corrosion. Once again, contact cleaner is the recommended tool, WD40 happens to work fine for me.

Step 9: Tuning System

Picture of Tuning System

Dials and dial strings.
Many a radio serviceman would curse the lowly dial string. They are a pain in the rear to restring and the only place I am aware of that sells dial string is antique radio supply. Best thing to do is not mess with it unless it's broken. Lubricating the pulleys and tuning knob shaft are a good idea. Something like CRC on a q-tip is a good way to accomplish this. Do not get it on the string. You want to lube just the pulley shafts and the tuning shaft bearing.

While working on the tuning system it's a good idea to clean and inspect the the tuning capacitor. On some AA5 radios the tuning cap was mounted on rubber bushings. Make sure those rubber bushings are still in place. If not, you'll have to get creative with rubber grommets or something similar. If everything is intact go ahead and clean up the fins of the tuning cap using either a can of compressed air or a soft bristle brush. Be careful not to bend them. If you see a bent one, carefully straighten it out using your finger nails.

Step 10: Speaker

Picture of Speaker

Finally, the speaker.
Vintage radios used electrodynamic or permanent magnet type speakers. Electrodynamic speakers used a field coil instead of a magnet. Permanent magnet speakers don't have the external field coil. They both have pros and cons. The electrodynamic will never lose its magnetic field unless it goes open but if the speaker cone is damaged it can be a challenge to repair. The permanent magnet speaker is easy to replace but many of the old ones have weak magnetic fields due to a poor understanding of magnetizing metals at the time. If you have a permanent magnet type and it requires replacement, a trip to radio shack or a car stereo shop may solve the problem. You don't need anything fancy as the AA5 produces maybe 1 watt of audio.

A word about electrodynamic speakers.
They are not directly interchangeable with regular permanent magnet speakers. The field coil in the electrodynamic speaker is actually part of the radio's power supply circuit. It's used as a choke. If you have an electrodynamic speaker that is absolutely trashed and can't be saved you have two choices. Find a similar replacement (good luck) or do a little bit of re-engineering.

The re-engineering consists of removing the whole thing and installing a choke coil of similar value and using a permanent magnet speaker OR keeping the old electrodynamic speaker in place (so the field coil is used) and finding a replacement permanent magnet speaker that fits inside the radio.

If you opt to keep the old electrodynamic speaker in place AND install a new permanent magnet speaker you'll have to disconnect the leads that go to the old speakers voice coil and run wires to your replacement speakers voice coil. In some radios there is plenty of space to mount a replacement speaker, in some there is not. Typically the old speakers were in the neighborhood of 3-4 ohms so pretty much any full range speaker you find will work except for some oddball Bose speakers that where 1/2 ohm impedance.

If you find yourself tight on space you might want to consider removing the old cone and voice coil from the electrodynamic speaker and finding a replacement permanent magnet speaker that will fit inside the basket of the old speaker. Yes, you'll end up with something that has a smaller cone but it may be the only viable option. I have taken this route on a Philco radio and it worked out for me. The thing to watch out for here is that the new speaker fits into the basket of the old speaker without sticking out too far.

My cone is torn but looks savebale, what to do?
It's arts and crafts time my friend. If you have an electrodynamic speaker, your best choice is to try to fix it. I have successfully used paper towels, rubber cement, and spray paint to fix old radio speakers. Use a fresh container of rubber cement so it flows easy. Gently apply a thin coat of rubber cement to what's left of the speaker. Once its coated with glue, cut a piece of paper towel to fit the repaired area and carefully lay it in place. Gently press the paper towel in place with your finger tips being careful not to make any further tears in the old cone. If the cone is brittle it makes sense to do the whole cone and be done with it. The sound will change and the radio will be more mellow and may not play quite as loud since the cone is now heavier. Mellow sound is better than no sound.

Spray paint the cone brown so your repair is better hidden. Some AA5 used a speaker grill with no cloth so a white speaker will attract attention to itself. Make a cardboard cutout with a hole for the speaker and carefully spray paint the speaker right where it's mounted. Do not remove the speaker unless absolutely necessary. The cutout will prevent overspray. Let the whole thing dry overnight.

Step 11: Antenna

Picture of Antenna

The antenna.
Most if not all AA5 where equipped with wire loop antennas. These antennas consisted of many feet of enameled thin copper wire in the form of a coil about 6-10 inches in size. The coil was usually mounted on the back cover of the radio but sometimes was even part of the cabinet. There isn't much to go wrong with these other than maybe a broken wire. Close inspection will reveal where the broken wire went. Replace it with something similar. If you cant get enameled wire, a single strand unwound from an old copper lamp cord (maybe even the cord you replaced) will do the trick.

Step 12: Feeling Lucky?

Picture of Feeling Lucky?

Get ready to reassemble and cross your fingers!
Double check that all your tubes are in their correct sockets. Turn the radio over and look over the wiring making sure that things that shouldn't be touching aren't. Carefully visually inspect all the original wiring and make sure you haven't inadvertently flaked off any critical insulation and shorted something out. Once all your repairs and inspection are done and the radio is all put back together, it's time to cross your fingers and plug it in.

Remember this is a live chassis radio! Do not touch any metal parts after its plugged in!

Flip the power on for about 5-10 seconds and then back off. The dial light should have come on brite and then dimmed down before you shut the power off. Give the radio a sniff test. If nothing smells like it blew up then go ahead and flip the radio back on and turn the volume control up about half way. You should have audio in about 30 seconds or so. A loud 60hz hum or squealing noise indicates a problem.

If you get a rushing noise (static) you're doing good. Go ahead and try tuning something in. if you get stations coming in go ahead and jump around a bit and feel good about yourself. If it's receiving stations, let it play for a couple of minutes then shut it off and give it a sniff test. The only thing you should be smelling is WD40 (if you used it) and old radio smell. Any burnt smells or smoke are a bad thing and you'll have to dig back in to see what's wrong.

A word about what an old radio smells like...
Tube radios exude a particular smell unlike any modern equipment. The heat of the tubes on the dust inside the radio, the contact cleaner you used, the insulation on the wires, the old waxed fabric cord, all exude their own smell. Most old radio fans immediately identify it as tube radio smell. Its normal. Its part of the nostalgia. Don't confuse it with burning smells or overheated smells. Unfortunately this is something you learn from being around old radios and you cant learn any other way. Don't be afraid to blow one up trying to fix it. You have to learn somewhere!

Step 13: Troubleshooting and Enjoyment

My radio doesn't quite work right!

It hums! If you replaced the filter caps, there's a chance you have a weak rectifier tube or a bad audio amp tube.

It's deaf! Make sure your antenna is ok and wired properly. Try turning the radio. The antenna is directional. If that doesn't solve it you may have a weak tube.

It doesn't play very loud before it sounds fuzzy. You may have a weak audio amp tube. Peek inside the cabinet while the radio is on (remember not to touch any metal so you dont get shocked!) If you have a tube that has a deep violet or deep blue glow inside the glass while it's powered up it may be a worn audio amp tube. Note the position of the tube on the chassis, UNPLUG the radio, get the tube out and look up it's number on the web. If the tube comes up as being an audio amp tube it probably needs replacing . A common audio amp tube on AA5 radios is the 50L6 and the 35L6. They are cheap and easy to get from tube vendors.

I get a raspy buzzing noise between stations. Electric eye lamps (lamps that turn off during the day automatically) have been known to create nasty noise on AM. Check on a known good AM radio to see if you get the same noise. If you do, your culprit is not the radio itself.

Radio sounds good at first then begins to sound distorted as time passes. You may have an out of spec resistor. While the radio is on, peek inside the cabinet being careful not to touch any metal so you don't get shocked. Look for a tube who's metal structure inside is glowing orange or red like its gonna melt. I'm not referring to the heater filaments as those are supposed to glow orange. If the tube structure itself is glowing from heat you may have a bias problem which is more than likely in the audio amp circuit of the radio. Obviously you can't perform this visual check on all metal tubes. Either way, it's time to get out the schematic and meter.

Following these same instructions I have resuscitated several old tube radios. The AA5 was built for simplicity thus there isn't much to go wrong and they are forgiving. Once your radio is up and running, enjoy it. Use it every so often. Just like an antique car, its bad to have it sit unused. Fire it up every now and then and show off your work!

into old tech? follow me on instagram as vintagetechguy to see random pics of interesting old tech.


cesperon (author)2015-07-27

I have to say. I have never read through a single instructable.. most of them are useless dribble or sharing information a 3 year old could figure out. BUT.... I not only learned something (a lot of somethings actually) but I actually read every single word and enjoyed the article! I actually enjoyed it so much I shared it with others! Perfect mix of information and humor... keep up the excellent work. (Did I flatter you enoug to fix my vintage radio for me? Lol)

jveazey (author)2017-07-24

One thing I would have added is using a dim build tester for initial powering.

Criticatlarge (author)2016-09-02

Very kewl instructable, kudos! FYI.. good old brown-paper-bag paper
works well also for speaker repair, it's stiffer and more closely
matches the tension in the cone.

Thanks for the lesson :)

Skipkeyser (author)2016-07-14

Very useful instructable. I would only add "take a lot of pictures - before, during and after." Especially easy in the age of digital photography and invaluable when you discover you forgot to make as detailed a set of notes as you thought you had.

IanO8 (author)2015-09-28

I am looking for a replacement bulb for my Zenith J880 radio/record player. However the only markings on the base were "USA". It has the bayonet style base, but it has 2 contacts instead of the one that the type 47 base bulbs I am finding online have. Any idea as to what type of bulb I should be searching for?


jackscrap (author)IanO82016-04-23

I found that my boxes of tubes, mostly nos, all have the labels printed on the glass. look at the tube, watch how the light reflects off it even though the paint may be gone you may see a shine ghost of the printed label. Failing this try looking at for the schematic that will have the tubes labeled, it is possible some of the tubes were re-arranged wrong, or replaced with something that doesn't belong(this is the only tube Grandpa had and it fits the socket, Bingo. WRONG) Remember when repairing something, the last person who had it couldn't fix it, don't trust their work.

130104 (author)IanO82015-10-04

i found all my tubes at the guitar center brand new

ke4mcl (author)IanO82015-09-29

look in the socket and make sure it has two contact points in the center. a two filament bulb in a radio is kinda odd. they did make bulbs that had two filaments, one side of each filament was connected to the socket and the remaining leads connected to each contact under the bulb. those bulbs though not the right ones, will sometimes work in a single center pin socket if wiggled around enough. i'm not familiar with your model radio but i'd want to make sure that bulb belongs there.

JohnnyM5 (author)2015-05-18

What do i need to read/watch so i can learn everything i need to know in order to fix this? Also could you tell me anything avout this radio like the year? I work for a moving conpany and a lady was throwing this away i thought it was really cool so i took it and niw i want to get it working. Any information will be greatly appreciated.

ke4mcl (author)JohnnyM52015-07-28

i think what you have is called a farm radio. for places that had no commercial power, they sold radios that looked just like their city brothers but ran on batteries. electronically they are very similar to the AA5 but the circuits were designed to be run off a battery bank that consisted of heater, plate, and sometimes a bias battery. they would be called A, B, and C batteries. A was plate, B was heater and the biggest, C was small if even present as not all radios used them.

JeffF48 (author)ke4mcl2016-04-07

oops--A is for filaments or heaters, low voltage typ 1.5V to 6V, usually able to supply more current than the other sections; B is the plate supply much higher voltage than A, typ 22.5 to 135V; C is the negative grid bias usually 1.5 to 15V doesn't need to supply much (if any) current.

The newest radios I can think of that use A,B,(C?) batteries are the pre-solid state Zenith Trans Oceanic models. ISR the batteries were built into a single block integrating A,B, and C together.

As far as exchanging A and B batteries-- some tube-type hearing aids had the same shape and size separate A (1.5V) and B (15 or 22.5V) batteries. Needless to say, ignoring the warnings and exchanging these batteries causes the normally almost invisible filaments to light up brightly, but only for a few seconds, before burning out.

Batteries from these old days were made from series connected multiples of 1.5V cells-- look inside a 9V battery for a contemporary example. You will find either stack shaped cells, or one or two brands use tiny quad-A (AAAA) cells.

acours (author)2015-12-29

Well i was going to sleep and instead found this gym. Just picked up a vintage RCA Victor 3-bx-671. The guy said it just had a bad tube, which i have the replacement on the way now. Got to redo all of the dial chords too. Can't wait to get the guy running though. Awesome instructable!

ke4mcl (author)acours2015-12-30

"Just has a bad tube" is generic for "I have no clue and thats what everybody used to say."

Be careful. If it hasn't been recapped yet, you're bound to end up with a buzzing radio best case, smoking radio worst case.

MatthewM87 (author)2015-10-05

This was great--thanks for sharing these tips with a new generation and demystifying troubleshooting tube electronics. Exactly what I needed to restore an old Philco 42-380 cabinet radio!

wbogen (author)2015-10-02

A great instructable, really well-written. Takes me back to when I was 10 or so and our big wooden console B&W TV would stop working. I'd pop off the back (while it was on! Amazing I didn't get zapped.) and see which tubes weren't glowing. I'd pop those out, take them to the 5 & Dime, and put them in the tube analyzer machine they had to verify they were busted. Open the cabinet in the analyzer to pick out replacement tubes, take them home, plug them in, and get back to watching 'The Twilight Zone'.

maswoodalamkhan (author)2015-04-29

The Vacuum Tube Number ECC 83 in my Grundig radio seems defective. I have one good tube called ECH 83. Can I replace ECC 83 by ECH 83?

ke4mcl (author)maswoodalamkhan2015-07-28

nope. ecc83 is same as 12ax7 which is available at most music stores. its popular in guitar amps.

oz5es (author)2015-05-14

Watch out, not to handle the tubes, touching the printing on them, on many tubes it just wipes off.

GL de oz5es Ebbe

ke4mcl (author)oz5es2015-07-28

fortunately thats mostly a euro problem. the brand on american glass tubes was often in easy to remove ink but the tube number itself was not unless it was a rebranded euro tube sold by an american company.

maswoodalamkhan (author)2015-04-22

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)maswoodalamkhan2015-04-22

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.

maswoodalamkhan (author)ke4mcl2015-04-22

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 (

JakeL6 (author)2015-03-15

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

glennby (author)2014-10-09

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 (author)glennby2014-11-09

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

Thanks again.


ke4mcl (author)glennby2014-11-09

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 (author)ke4mcl2014-11-16

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)glennby2014-11-03

this sounds like an RF issue which unfortunately may require special test gear.

MarkS4 (author)2014-08-06

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)MarkS42014-11-09

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)MarkS42014-11-03

i rebuilt one of those. didnt need the schem. not much different than working on AA5's.

kong2550 (author)2014-07-23

thank you

bob3030 (author)2013-09-25

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_E (author)2013-07-27

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.

mlmccauley (author)2013-07-27

Excellent explanation of a technical topic in a manner understandable by non-technical people. This is where we geeks almost always fall short.

sbloomfield1 (author)2013-05-31

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

gravityisweak (author)2013-05-30

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)gravityisweak2013-05-30

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.

carchub (author)2012-05-14

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)carchub2012-05-15

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 (author)ke4mcl2012-05-15

Totally worked, and I got the number, 50L6! Thanks again

carchub (author)2012-05-12

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)carchub2012-05-13

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 (author)ke4mcl2012-05-13

Thanks so much! I can totally see the set screws on them =D

jjjjwiz (author)2011-06-27

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)jjjjwiz2011-06-28

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.

stienut (author)2011-05-01

Super ible. I can't wait to see what's up with my 1936 American Bosch. Very well done, indeed!

CBTman01 (author)2011-01-09

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)CBTman012011-01-10

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.

maxstevenson (author)2009-03-06

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.

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