Step by step antique radio repair and upgrade

I actually have a 3 very similar radios. I think I need to do this.[M3talhead] takes us through a very informative repair of an old tube radio. In this case, his radio was from the late 30s. He was able to find the original data from Radiomuseum.org. He painstakingly dismantles the radio components and the cabinet. Instead of completely modernizing the internals, he replaces the bad parts and brings it back to functionality. He wanted to do an MP3 upgrade, but rather than wire directly into the radio, he built an AM transmitter for his mp3 player.

Comments

  1. wouter says:

    I’m going to mod my brAun 199 (1975) so it will be sort of like a squeezebox.. but the restoration is taking far more time than I thought..

  2. Joe says:

    It is great to see someone restore a nice looking old radio. I have done quite a few myself and would like to add a few comments.

    First, NEVER plug in any old tube equipment to “see if it works”. Most likely, the electrolytics are dried out and may be shorted, which could cause damage to the rest of the radio.

    Second, assume that ALL the capacitors in the radio are bad and need replacing (except the silver mica caps). The electrolytics are dried out and the paper/beeswax caps have absorbed moisture. I’m not sure why the OP used mylar caps when replacing the electrolytics. You can keep the electrolytics (the big cans) on the chassis for looks. just cut them out of circuit and replace with modern parts underneath.

    One place to get these high voltage caps is an outfit called justradios.com. He stocks the values needed for old tube gear.

    I would do a restoration in a slightly different order than the OP. The first thing after a general cleanup is replacing the caps. Then go through and check the resistors. They will probably drift high in value over time. Replace as needed. Only then should you worry about checking the tubes. Most of the time, the tubes are fine. Use a good quality tube checker, not the type that was common in stores for use by the average customer. Those were designed to fail good tubes. Unless you like wasting money, don’t just replace all the tubes.

    In radios with power transformers, make sure the transformer is still ok and the windings are not shorted. On the common AA5 radios, there is no power transformer. Speaking of AA5 radios, you should use an isolation transformer when powering these up so you don’t electrocute yourself.

    One last step that is often needed is an alignment of the radio’s RF and IF stages. You will need some basic equipment like a signal generator and some alignment tools. The procedure is not hard and is usually documented in the radio service data that you will find on the sites mentioned by the OP. For pre-WWII radios, look for “Rider’s”, which was like the later “Sam’s Photofacts”.

    Some early radios used rubber insulated wire (late 30’s Philco in particular). If so, the rubber will have hardened and cracked, leaving lots of bare wire. Moving this wire to replace parts will make things worse. The best course of action is to simply sleeve every wire with heatshrink tubing by unsoldering one end. It’s a pain, but necessary with rubber insulated wire. If you have cloth covered wire and it looks ok, leave it alone.

    If you have a variac, you can slowly bring up the AC power to your just repaired radio. This is a good idea, in case something is shorted or something is miswired. Remember, you’re dealing with high voltage here. If you don’t have a variac, make a simple “dim bulb tester” (google it).

    There are other subtleties involved in restoring old tube equipment, but the basics I’ve outlined will take care of most situations.

    Some of these old radios were very attractive. It is very cool to listen to your favorite music or programs on a classic tube radio. Just like Dad, Grandad, etc. used to.

    If you want a high quality AM transmitter to broadcast to your newly restored radio, I can recommend the kit from sstran.com. Any of the less expensive transmitters are junk and will drift badly.

    Joe

  3. Truthhertz says:

    @Joe-

    I *would* check the tubes… at least to this extent:

    First, make sure that they are the *correct* tubes in their *correct* positions. You never know if some dufus before you– someone who thinks that all old radio problems stem from tubes– didn’t mix them up or even insert the wrong kinds because he had some extras lying around.

    Second, I would at least check filaments for continuity… something easily done with an ohmmeter. Of course, if you turn the set on and visually see that they are all lit, fine, but that’s not always the case.

  4. Dave says:

    Re. Any ideas about plugging or wiring modern audio kit (like an mp3 player) into an old radio – DON’T! Well, not unless you know exactly what you are doing in the way of isolating the connection. Early UK radios had a “live” chassis, i.e. one side of the mains was directly connected to the chassis, which could prove lethal at the UK voltage of 240, a resistive dropper being used to supply the voltage for the valve (tube to you folk across the pond!) heaters. I imagine USA versions would be no different in principle, so be careful. There was nothing in the way of mains isolation in “the old days” !!

  5. Joe says:

    @Truthhertz

    I didn’t say not to check the tubes. Just that this isn’t the first concern, as most people think. The tubes should definitely be tested.

    I have a 1932 Philco cathedral-style radio. As old as it is, I only replaced one tube because it was weak, not totally bad. OTOH, I recently did a car radio for a Nash and it had three bad tubes.

    Joe

  6. Joe says:

    @Dave

    Good advice. I was going to mention that as well, but forgot. Interfacing modern electronics to old tube gear can be very hazardous to you and your equipment. The safest method would be some type of optoisolator.

    Many American tube radios also were connected live to the AC wall outlet. This design is called an AA5 (All American Five). It has no power transformer and uses five tubes. The tube filaments were connected in series, so that the total voltage drop was aproximately 115V. This saved the manufacturer the cost of a transformer. What is even worse is that in this design, usually the metal chassis is hot and the neutral is switched — DANGER WILL ROBINSON! This is the reason I suggested using an isolation transformer.

    Joe

  7. hoodoo says:

    fuck instructables.. stop posting links to instructables

  8. Joe says:

    Again about interfacing your MP3 player to the radio. The original OP was smart and used an AM transmitter, which requires no hazardous interfacing and is the safest method.

    The transmitter design that he used will do the job, but is on the level of a Mister Microphone toy and will sound like crap. It also can’t be tuned to another frequency if 1KHz is in use in your area.

    The SSTRAN kit that I mentioned is the least expensive, good quality AM transmitter that I have found, and I have looked. I bought two over the years.

    Joe

  9. Joe says:

    @hoodoo

    I agree with your sentiment. Instructables is a nuisance unless you’re a member (I’m not).

    If you don’t need the pretty pictures, just follow the good advice posted in these comments by myself and others.

    Joe

  10. Jordan says:

    I got a Philco 16B cathedral radio for almost nothing in the summer. It’s in horrible shape but I figured it might be a good project to restore the thing some day. The wood cabinet is trashed :(
    The rectifier is burnt out, likely from it being turned on after however many years of sitting untouched.
    Anyway the article and posts here are great and I’ll be checking back if I ever get around to working on it!

  11. Joe says:

    @Jordan

    Here are a few sites with info about your radio. There was also a later Philco 16B that was a “tombstone” shape.

    http://www.tuberadioland.com/philco16_cathedral_main.html

    http://www.philcoradio.com/phpBB2/viewforum.php?f=12

    Here is a picture of my Philco 52: http://goo.gl/CGee8

    Good luck on the radio.

    Joe

  12. Fallen says:

    Agreed on the instructables. That site is a pain to navigate.

  13. Mike says:

    Joe is an idiot. Go hack something and shut up.

  14. AussieTech says:

    I had a British set marked “AC Only” with a (heater) transformer which nearly killed me because it still had direct on mains live chassis HT, so don’t just assume a tranny means an isolated chassis!

    Happy and safe restoration fellas.

    (Instructables – a good idea badly done.)

  15. strider_mt2k says:

    Agreed.

    Great project.
    and
    Instructables BLOWS

  16. lwatcdr says:

    For most people I would think that they way they would interface modern electronics to an old radio would be replacement.. I found an nice old that was missing all of it’s electronics. I was very tempted to fill it and MP3 player and modern radio. A friend of mine is into old radios and had a one that would fit so I gave it to him.

  17. Toob Noob says:

    I started with a project like this, intending to replace the old electronics with new. Went with a close visual inspection, removed the original unit, spent a couple of hours gently cleaning the accumulated dust, googled around for the schematics, found them (!) and started getting curious about this thing. I’d never worked with anything tube-based before, and probably wouldn’t again, so… no time like the present.

    It already had an isolation transformer built into it. Most of the wiring looked OK, so I tested a few caps (in-circuit, which is poor practice) to see if the values were sane, and they were. Dog-bone style resistors were correct (had to Google around to figure out how to read ‘em!) Got really curious and decided to grab a Variac and fire it up (against good practice) “just to see” what would happen (I GOT LUCKY. DON’T DO THIS!) But after a few moments, when the tubes started getting warm, I turned the lights out (so I could see which tubes were glowing) and turned the Variac up.

    At around 3 in the morning, this hunk of 75-year-old unrestored hardware was producing a dim orange glow from the tubes behind it, a pretty white glow across my bench from the light bulbs that illuminate the dial… and music for the first time in about 30 years.

    At which point I forgot about the MP3 player. The line cord was slightly frayed and was replaced the next day.

    Since then I’ve done some googling to find out ways of making replacement caps that looked like the originals, and have replaced ‘em. The only change to the unit is a little sticker placed inside the metal frame for the next servicer/restorer to see it: “Tested/working 2009. Embedded modern electrolytics in wax/cardboard tubes, replaced original caps 2010.”, and a small bag stapled to the cabinet, labeled “original capacitors ca. 1935″)

    One spot didn’t get cleaned – the part where I saw my grandfather’s initials and a date written in pencil – he must have worked on it some time in the 60s. There was also a thumbprint nearby. So I put a big greasy thumbprint next to his, along with my initials and a “2010”. Over the next few decades, that thumbprint etch itself into the metal, just like his, and said “Thanks, Gramps”, as I contemplated that he’d been hacking hardware before I was born.

    Thanks for this project. (Dammit, something in my eye. Must be all the solder fumes…)

  18. Joe says:

    @Toob Noob

    Aren’t you glad you didn’t gut that radio and make it “cool” with modern electronics? I’m sure it means much more to you in restored condition. Your Grandfather would be proud.

    What is the make/model?

    Joe

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