SAFETY FIRST!

So, you find yourself the proud new owner of some not-quite-so-new tube radio or amplifier and you have made the choice to try to bring it back to life. NEVER! plug in an old tube radio or amplifier that you found in the garage/attic/flea market/wherever without first performing a careful and thorough electrical inspection (detailed below). Many people want to plug it in "just to see if it works" or "just to try things out." NO, NO, NO! This is a MONUMENTALLY BAD IDEA!

DO NOT PLUG IT IN! This is the single worst thing in the world to do with antique electronics! If you are lucky (and few of us truly are), all it will do is hummmmmmm. If you are not lucky (yes, this probably means you), a rush of electricity after decades of sitting around and deteriorating is likely to kill old capacitors, creating cascading failures that can blow a rectifier tube, destroy other downstream components, or start a fire... A shorted rectifier can permanently destroy an irreplaceable vintage power transformer or power supply inductors. A typical power transformer for a tube radio produces about 700 Volts! Dried, cracked, and missing insulation from old wires can come into contact with the metal chassis and can electrocute you!

The BEST practice for dealing with old tube radios is to CUT OFF THE POWER CORD right away! First, it probably needs to be replaced anyhow, and second, this keeps anyone else from plugging it in until you've been able perform a thorough inspection.

Where it All Started:

My wife and I were browsing the local antique market one day when I came across this nice little gem. So, here are a few photos of its "found" condition. Yuck, all covered in dirt, of unknown functional condition, and the push buttons on the front look like Crasins. My goal was to make it look and sound like new - I suspected this would take some effort. Both the wooden cabinet and the electronics chassis inside need some attention and care, though the cabinet is in fairly nice condition for its age. This radio was introduced in the later half of 1939 and production continued into 1940. The radio features seven tubes and receives AM broadcasts from 550 to 1500kHz, police band from 1.55 to 3.4 MHz, and shortwave from 6 to 18MHz. The original selling price was $69.95 (interestingly, this is the equivalent of nearly $1,200 in 2013 dollars) and 129,076 were produced. I have always had an interest in music, old things, and electronics. What an interesting convergence point among these interests... Plus, I LOVE to tinker with things to learn how they work.

Some Forum Discussion about this project can be found here and here.

Wooden Cabinet Cleanup:

There are several paths to returning the cabinet to its original appearance. At the easy side of the spectrum is a thorough cleaning and restoring the little bumps and bruises that it has accumulated over the years. The other end of the spectrum is reserved for the worst of the worst and involves performing a total strip and starting all over again. Like most things in life, there are many intermediate stages that require some work, but that do not necessitate the intensive labor of a full strip and refinish. Although there are MANY little nicks and what appear to be water spots/drips down the side of the cabinet, there are no major gouges and more than 95% of the original finish appears to be intact. The overall surface is a bit rough in a few places, but there doesn't appear to be any structural damage to the wood at all.

Here is a close up of some of the front of the cabinet. The lacquer has some minor cracks and areas of separation from the wood on the front panel. I decided to leave this area alone and keep the entire cabinet in original condition. Most of the minor damage in the images above appears to be the result of water or some other liquid that splashed and ran. There are also a million little scrapes around the bottom of the cabinet that are visible in the images above. Overall, this 70+ year old cabinet is in pretty nice shape! All it needs a little clean up... 

After Some Cleanup:

The great folks over at the Philco Phorum and Antique Radio Forum recommended cleaning the cabinet first. You want to use a non-water based cleaner for this, so it doesn't damage the wood. Products like Goop and Gojo are ideal for this task (be sure NOT to use the kind with pumice/grit in it!). Work outside, or at least on a drop cloth. Start with a clean, soft cloth and ALWAYS wipe WITH the direction of the grain, NEVER across it! Spread a thin layer on, gently work it into the crevices and corners, let it sit (or run as may be the case) so things soften up a bit and then wipe it away. Being GENTLE is the key here. Rub too hard and you'll scratch up the lacquer finish. So, after spending about an hour with a tub of Goop, my radio looked almost new again! WOW - Just look at what was hiding under the built up crud! If you have a choice, I recommend using Gojo as it has a much less offensive odor than does Goop... If your radio is especially dirty, it might take several applications of Gojo to get all of the dirt off. It it took 70+ years to build up, it won't all come off at once... If you still have a fair amount of the original lacquer left on the wood, your first application of Gojo will leave a very impressive and shiny surface behind and you'll think "wow!"  But, you'll look at things again in a day or two and think "hey, where did the shine go?"  It's a terrible tease... Let things dry for a few days and carefully inspect the cabinet under a bright light or outside in the sunshine. This will reveal places that need more cleaning - typically in corners and cervices. An old toothbrush, used gently with some additional Gojo, can help clean out some of the harder to reach places. Now you need to let it dry for another few days. 

It took a little time and effort, but I was thoroughly surprised at what was hiding under 75 years worth of crud and dirt! 

After a good cleaning, you can see that some of the marks on the cabinet have eaten into the finish a bit. Since so much of the original finish is intact (I'd estimate the original finish is about 97-99% there), I used some Howard Restore A Finish to even out some of the color issues. It comes in a variety of colors to match different lacquers - Cherry is a pretty close match to this specific radio. Let the cabinet dry for a few days after using Gojo/Goop - it leaves a "wet" and shiny residue behind that will slowly evaporate with time. When using the Howard product, just follow the directions on the container. Always wear rubber gloves, old clothes, work outside, and ALWAYS rub in the same direction as the grain. Have a look at the before (as found) and after (first Goop, then Howard). The Howard Restore-A-Finish is just about the closest thing to "magic in a can" that you can buy for restoring old finishes! Be sure to use the Howard stuff OUTSIDE, though- it stinks! 

Both images of the cabinet above are lit by flash and were taken from roughly a similar vantage point. If you look from an angle where the light reflects, you can still see the disturbances in the finish, but the color issues have significantly evened out. The cherry colored Howard might just be a pinch dark for this cabinet, but perhaps I'm also reacting to the differences in surface reflectivity. Overall, I'm tremendously impressed how such a little bit of effort made such a nice improvement in the appearance! With all of the distractions gone, you can see the nice patterns in the wood grain again! What an improvement!

If you've got bare wood after a good cleaning, you've got a bit more work to do. Howard Restore-A-Finish works best if you've only got some light marks/scuffs in the lacquer finish. It has solvent-type ingredients that will allow some of the existing lacquer to "re-flow" somewhat and even out some of the minor scratches and abrasions. The dye in it will help even out some of the color issues you might be experiencing, but it may not do quite as much where the existing lacquer finish is just plain gone. Depending on how bad things look, you've got a few options. Pick some place on the bottom trim around the side to experiment on, and do so only in a small area to see how things turn out. The trim, though, is hardwood, so it will behave differently (likely absorbing less color) than the larger and flatter spots that are wood-veneer (likely to be more porous, thus absorbing more color). Everything in this game is an experiment until you gain some experience.

What you choose to do also comes down to personal preferences. Some people prefer to keep things as "original" as possible. They have an experienced eye and are highly selective about what radios they will acquire in the first place. These types of people will not acquire a radio that has been refinished as a matter of principle. Others choose the nastiest cabinets they can find (bonus: they also tend to be inexpensive) and have honed a skill set at serious restoration (replacing trim, filling in chunks of missing veneer, repairing cracks in the wood, wetting and reforming curved wood, etc).

First option: have a look at what Ron calls "the treatment." This can go a long way to evening out the color of a scratched wooden cabinet. He has several comments where he describes his technique for blending in missing colors and scratches. I've not have much success duplicating his results. I've tried it on an old Freed-Eisemann radio wooden cabinet and after a short while (few days), the light spots are back like I never applied any of the scratch cover at all. Perhaps the finish on this cabinet is just too far gone... Perhaps I'm not scrubbing hard enough... It's hard to tell...

Second option: pick up some Howard restore-a-finish. Cherry color is a pretty good match (but ever-so-slightly dark) for this cabinet. Use a paper towel and just dab some on in a small spot to see what the color looks like. Let it sit for a few minutes, then give it a gentle wipe with a clean cloth. If you've got what appears to be raw wood, the results will be a bit unpredictable, so stick to a small spot until you see what happens. This stuff will also leave behind a "wet and shiny" look until it fully dries/evaporates (another few days). Additionally, you might want to try different colors. Perhaps start with a color lighter than Cherry to see what happens. You can always go darker, but once applied, you'll never make it lighter again... This stuff costs about $10 a can, get the smallest can you can find - a little bit goes a long way and the contents will last you a long time.

Based on my limited experience, you might have more success with Howard than with furniture scratch cover. Give it a try and see what happens. It might take several applications over the course of a few days to get the colors to match more closely. If things are going well, give the entire cabinet a good wipe down with Howard after evening out some of the lighter colored spots. Patience is the key. Don't try to accomplish too much too quickly. This cabinet is nearly 80 years old, a few more days or weeks (or months - you know how life gets in the way of things...) of careful and patient work will pay dividends.

Once your color is evened up a bit and you are happy with how things look, you have a choice to make: do you leave it as is now, or do you apply some clear lacquer to seal up the finish and even out the surface appearance? Lacquer, like paint, comes in different colors and different finishes (matte/satin, semi-gloss, and glossy). Each radio had a different original look and very few radios were finished in high gloss - it just looks too shiny and won't be "right." I tend to go with matte/satin or semi-gloss. Using lacquer is also something that needs practice on a scrap of raw wood first. The temperature needs to be right (50-70F) and the humidity needs to be LOW (30-50%). Cold temperatures make lacquer take a long time to dry. High humidity will cause a milky color to appear in your finish. Before you apply lacquer, make sure the wood has "acclimated" a bit first by keeping in the house where you can control humidity and temperature. You don't want the cabinet to suck up humidity from a stretch of rainy days and then seal it in on the very next day when it is sunny and warm.

A third option (which applies only to a limited situation) is to attempt to reamalgamate the original finish. This applies to what is often described as a "crazed" finish where the original lacquer is still in place, but looks like it has dried and cracked in all random directions. This technique requires a little bit of practice first, but can work rather well if you've got a significant amount of the original finish still intact.

A fourth alternative gets more involved: to re-finish just part of the original surface. Sometimes, depending on the surface of the cabinet and the location of the damage, it might be possible to "mask off" a small area where the wood changes and apply some clear lacquer to seal the wood, add some toner lacquer to reduce the visibility of the missing color, and then add a few coats of clear lacquer on top. Do this only at the transitions of physical pieces of wood, never "in the middle" of a wooden panel as the results will be completely obvious and not look right. This is just like painting a wall in your house - to get good results, you always have to paint the WHOLE wall, never just a patch in the middle. Some time ago, I stripped and refinished just the top surface of an old table. It took a bit of effort to get it looking nice, but was a successful project that only took a few days of on and off work.

Finally, if you've got a cabinet that is just beyond hope, you might be looking at a complete strip and re-do. This often involves a GREAT deal of work and is really only an option of last resort. If your cabinet needs a complete refinish, I recommend doing some reading and practicing first. There are several great threads about creating beautiful lacquer finishes. One of the best is here: Philco 90 Cabinet Refinishing. This thread is a complete start-to-finish tutorial on how to refinish a wooden cabinet properly. Read it several times. Then read it again. I have completely refinished an RCA Radiola cabinet and documented my work here. There is a LARGE learning curve associated with refinishing a cabinet. Other threads on cabinet finishing are available here and here.

Each case will be different. I got lucky with my Philco find, the wooden cabinet only needed a good cleaning. The electronics, however, received a complete restoration.

Restoring Photo Finish:

The two outermost vertical bars that flank the speaker (the diagonal stripes) are called "Photo Finish" and are typically not a "standard" veneer. If these are damage, the repair is somewhat easier than replacing veneer itself. Here are a few resources about how to repair a photo finish: Do it Yourself Photo Finish, Jamie's thread on Photofinish Restoration, and another resource for photofinish.

Misc Cabinet Parts Cleanup:

Above is a before and after comparison of cleaning the speaker grille cloth. I used nothing more than a soft old toothbrush and my air compressor. Be careful how close you get to the fabric with the air compressor as you can alter the pattern of the weave with too much air pressure. 100 PSI from your air compressor is NOT your friend in this case. Start further away and gradually move closer to the fabric while gently scrubbing with the tooth brush until the dirt and grime are gone. Working this way, I didn't need to separate the cloth from the cardboard, or use any water at all which makes things much easier! 

Finally, above are before and after images of the escutcheon. A little bit of Goop and a gentle brushing with an old toothbrush on this removed years of grime, but also revealed a few speckles of rust here and there. Darn! I am not sure if I want to do anything further with this or not. The same brush and Goop treatment was used on the knobs as well to good effect.

At this point, I think I might be finished with cabinet work. I ordered a new set of decals for the knobs when I originally had thoughts of refinishing the cabinet, but I'm not sure that I'm going to use them now as this would require additional coats of lacquer to be applied. The online community urged that I leave the original finish alone and I have to say this was good advice. As one person said, "It's only original once."

The little burgundy buttons that poke through the holes in the escutcheon for push-button tuning are available at Renovated Radios for a reasonable fee. Use the ones marked "Philco Short Buttons." They are 5/8 inches long by 1/2 by 1/2 with a rectangular slot in the bottom 1/16 in. wide by 3/16 long. When you order these, be sure to pick up a set of Philco Chassis Corner Mounts (PHS-COR) as well. These rubber feet mount on each corner of the metal chassis and make sure that the push buttons line up appropriately with the holes in the escutcheon when you put the chassis back in the cabinet.

Electrical Chassis Restoration:

A Special Note of Caution: a number of radios like this have a speaker that plugs in to the back of the chassis with a 4-prong plug. NEVER power up the radio without having the speaker plugged in. The field coil in the speaker is often part of the power supply to the rest of the radio (nifty engineering move here- killing two birds with one stone). Powering the chassis without the speaker plugged in will cause a voltage surge on the rectifier that is likely to cause cascading failures in the rest of the circuit.

Before you do ANYTHING with your new antique radio, there are some safety protocols that you need to be aware of. Some of these protocols are intended to protect you and some are intended to protect your radio from further damage.

Safety Protocol for YOU:

First, there is a protocol to follow for testing tube radios/amps that needs to be followed BEFORE you plug the power cord into the wall outlet. Failure to follow protocol risks destroying old equipment, starting a fire, or killing yourself. A tube radio power supply harbors LETHAL voltages, often in the range of 200-400v. This voltage can be present EVEN WHEN THE POWER CORD IS UNPLUGGED. This voltage CAN KILL YOU. There are a few basic safety rules that apply here:

1) REMOVE ALL jewelry. ALL of it! NO rings, NO necklaces, NO bracelets, NO danglies, NO nothing that will accidentally conduct electricity!

2) UNPLUG THE DEVICE AND DISCHARGE ALL CAPACITORS. This is typically achieved by using a specially made (by you) insulated wire with insulated alligator clips at either end and a 10k-100k power resistor rated at 1 to 3 watts in the middle. USING ONE HAND ONLY, clip one end of the wire to one side of the capacitor. Using that SAME HAND again, clip the other end of the wire to the other side of the capacitor. Let it sit there for a minute and then move on to the next cap. Repeat this procedure for EVERY cap in the device. Use ONE HAND ONLY! Keep the other hand behind your back AT ALL TIMES. Exposing yourself to high voltage that spans both hands (and your HEART in the middle) is just asking for an ambulance ride! Tube amp power supplies make excellent defibrillators. A properly beating heart does not respond well to being defibrillated! You've been warned... Also, you'll find many people online just say "short the cap with a screwdriver." DO NOT DO THIS! This is potentially damaging to the screwdriver, to the equipment you are testing, AND TO YOU. This much power can literally blow chunks off the tip of your screwdriver. If this flying chunk of screwdriver tip hits you or someone else in the eye, you have a major problem. DON'T BE DUMB!

Safety Protocol for your RADIO:

DO NOT PLUG IN YOUR RADIO! No matter how tempted you are to "try things out" or "see if it still works" or whatever else, DON'T DO IT! You need to carefully and methodically inspect your tube gear FIRST so that you prevent doing even more damage than time alone has already caused. Here is my short protocol for things you want to inspect first. A much more detailed and thorough protocol can be found here: Trouble Shooting Antique Equipment.

1) You will need to remove the metal chassis that contains the electronics from its wooden cabinet so you have access to the electronics. Once the chassis is freed, take lots of pictures - closeup pictures from different angles. Photograph each tube and each connector to document its original orientation/placement. Recognize that tubes with similar pinouts may not be located in the proper sockets (thanks to the previous owner). Some tubes might be missing. Make notes on how things are wired and connected to each other. Note colors of wires, positions of wires. Label all of the tubes with masking tape. Draw a diagram of the chassis and label where each tube goes. Now remove the tubes, get yourself a old bath towel and lay it down on the table. Turn the chassis upside down on the towel and take lots of pictures of the underside before you touch/disturb anything. Use good lighting, take close ups that show details of where wires travel and what they connect to. Only then should you begin to poke further into the chassis. Your notes and images will become an invaluable resource when you start removing and replacing things. If you have an air compressor, this might be an excellent time to use it to clear out some of the old dust/dirt/debris. As always, use a bit of care not to dislodge weak/brittle wires or other structures. It might be best to blow some air across the chassis before your compressor hits maximum pressure to avoid unintended damage. 100 PSI is NOT your friend in this situation... Old wires and components dry out and become fragile/brittle over time and hitting them with the full force of your air compressor might break and dislodge things are aren't ready to disconnect just yet. Be gentle...

2) Inspect the power transformer with your ohm meter. Check the primary (AC power cord) for resistance - make sure the switch is turned "on" first. The primary winding should not be open (mega-ohms of resistance), nor should it be a dead short (zero ohms). Check each of the secondary windings for resistance. They, too, should not be open, nor should they be a dead short. These will typically measure tens, hundreds, or thousands (<10) of ohms. Check to make sure multiple secondaries are still isolated from one another. You should find mega-ohms of resistance (or infinite resistance) between different pairs of secondary windings.

Alternatively, you can use a dim-bulb tester to check the health of your power transformer. This protocol comes from Leigh from the AntiqueRadios forum.

One test would be to remove all tubes, then power up with your dim bulb tester. Searching the web for "dim bulb tester" will reveal many examples. They all work the same way - a light bulb is placed in series with your radio to protect the radio's transformer from a shorted condition. The bulb might light up very briefly at first but should settle down to dim or almost dark after a few seconds. If it shows any significant brightness for more than 10-20 seconds or so, you have a shorted transformer or shorted circuitry connected to the transformer. At that point you would need to disconnect all secondary wires, then try again. If the bulb still comes on, the transformer is bad. If not, trace the loose secondary wires to find the problem.

If everything looks good at this point, re-install all tubes except the rectifier. Bring it up again on the dim bulb bester. The bulb will light, hopefully not too bright. Measure the voltage at the transformer primary. Calculate the percentage (60v / 120v = 50%). Apply that factor to your nominal filament voltages. Then measure those filament voltages. If any are not close to your calculated value, that points to a possible problem.

Using a dim bulb test is only a SHORT-TERM (several seconds) test to verify the operation of the power transformer, to make sure your transformer, power supply capacitors, and rectifier tube are not shorted. Your radio will likely not work with a dim bulb tester in the loop because it won't allow enough electricity to flow to make the tube rectifier function properly (most have a minimum voltage requirement). Do your power up, take a few pre-planned voltage readings, then power down again. This whole process should take no more than 30 seconds.

3) This is probably a good time to make your first two modifications to your old piece of gear: add a polarized AC plug and add a safety fuse. Old AC power cords have plugs with two blades that are the same size so you can plug it into the AC wall outlet either way. This is a bit dangerous with old gear (switching the neutral line leaves the rest of the circuit in the chassis energized with 120v), so replacing the plug with a new polarized plug is a good first step. Then, follow the power cord back into the chassis and add a fuse to the "hot" wire. Do this somewhere AFTER the cord strain relief (where the cord physically enters the chassis) and BEFORE the AC power line hits the transformer, the switch, or anything else. You can use any type of fuse holder here, depending on how "original" you want to keep things looking under the hood. Typically, a 1A "slow-blow" fuse will provide adequate protection. I would not recommend using a fuse rated at more than 1A at all unless you have a "large" radio with more than 6-8 tubes in it. Some radios may directly indicate the power consumption of the radio on the metal plate that is riveted to the chassis.

4) Check each of the tubes for resistance. Identify what type of tube you have, the numbers are usually stamped in silver on the glass envelope, either on the top or the side. You might need to wipe the tube with a damp paper towel to remove the dust and grime before you can read anything stamped on the outside. Look here at Frank's Electron Tube Database or Google the tube number and find a pinout diagram or data sheet for it. This will help you identify the pins and their function. Start with the heater/filament pins - these are typically the pins that are connected to one another with a thin line in the tube diagram. Test them with your ohm meter for conductivity. Conductivity between the heater pins should reveal a small resistance - typically under 10 ohms. Make sure there are no other shorts across the remaining pins. Test the remaining pins in pairs, all combinations, one pair at a time with your meter. If any other pair of pins besides the heater pins show connectivity, you probably have a shorted tube that needs to be replaced. Ebay is a good source for replacing old tubes...

5) Inspect the power supply capacitors. You can perform one or two tests with your typical inexpensive Digital Multi Meter, and you can perform a few more if you have an expensive DMM. but NO digital multi meter (unless you've dropped a few grand on a bridge tester) is equipped to help you test what really needs to be tested in antique tube radios and amps: do any of your capacitors "leak." This is a simple test: caps are supposed to allow AC to pass and are supposed to block DC from passing. If DC passes through your cap, you have a leaky cap. The ONLY way to test for this is to remove the cap from the circuit, apply a working voltage (200+ volts DC) to your cap and see if any of the current leaks through. See here for how to build your own capacitor leakage tester. In general, "can style" electrolytics and rolled wax paper caps should just be replaced as a matter of course (see below). Sometimes, though, the power supply capacitors are somewhat non-standard (like in my RCA Radiola 17 radio). In this case, directly replacing caps is an extreme chore, so checking them for leakage before doing anything else with them is clearly worth while.

In case you missed it above, here is an EXCELLENT detailed writeup for how to thoroughly inspect a tube-based power supply BEFORE applying AC power. Be sure to read Max Robinson's write up about Trouble Shooting Antique Equipment. The first one-third of this document is very detailed and definitely worth a read to help keep you from screwing things up even worse than they are already likely to be from the simple passage of time. There are many, many things that go wrong with old electronics and each needs careful and methodical attention. Simply plugging in an old radio can lead to any number of complication including fires and ambulance rides! Be smart - do some reading and learning first!

An Excellent Video Series:

There is an EXCELLENT video series that someone put together for YouTube about restoring an old radio chassis. If you are new to this, here is a great resource. The link is the first of a 35 part series, so it's very thorough.

Philco 40-180 Electrical Restoration:

Before we go too far, I want to share a treasure trove of Philco service hints & tips that are worth a read! While specific to Philco radios, there is a ton of general wisdom here that is an excellent learning resource!

The chassis appears to be completely original, though the power cord is clearly newer that all of the rest. Removing the chassis from the cabinet revealed a bit of a mess. Looks like some liquids have found their way into the cabinet over the years. Ugh, lots of work here - both above and below the chassis. A quick inspection reveals the chassis to be in original condition with the exception of a "newer" AC power cord being added some number of years ago. All of the wires, resistors, and capacitors appear to be original. This is a good sign - no one else has worked on the set to screw things up for me... I'll have to do that on my own.

So, very slowly, very methodically, making lots of hand written notes and taking hundreds of photographs, I began to remove just about everything from the radio. Start with the tubes and be very gentle. The two tubes in the lower left of the image above are called "loktal" tubes - there is a center pin that locks the tube into the socket. This holds them in place VERY securely, but makes them a pain to remove unless you know the trick. There is a small, round bump stamped into the metal band that goes around the bottom of the tube (see below). Tip the tube in the direction of the bump (push from the top of the opposite side) and the tube should just pop out. A small drop of penetrating oil from the bottom of the tube socket on the center pin might help with this. 

As you begin to take apart your radio, be sure to LABEL everything - use little pieces of masking tape to identify tubes, capacitor cans, etc. DOCUMENT everything - describe what connects to what, which resistors, wires, caps connect to which tube pins, devise a counting mechanism for the pins (or follow the schematic) and use it consistently. Take PICTURES of everything - from multiple angles because wires often hide under other wires that obscures where they really connect. Then double check your notes for accuracy before you remove anything. Use separate plastic bags for screws and parts and then label the bags according to what those screws hold in place. Be methodical and careful, and you won't run into any problems when it comes time to put things back together again!

Once the tubes are removed from the chassis, this is a good time to inspect, clean, scrub the pins. A little steel wool or a fine sand paper works well here to scrape the oxidation off of the pins. Some electrical contact cleaner might help the process as well here. The tube sockets are likely to feature copper contacts and these should get a bit of a cleaning as well, but be careful not to use too much fluid here, see my note below.

Be extra careful removing the dial glass from the chassis. The glass is held in place by a metal bracket on each side and the brackets are attached to the tuning structure with a screw (shown above). After removing this screw, I needed to use a sharp screwdriver to gently pry the clip off of the frame. After removing the clip, I found out why it was such a challenge - the support frame for the tuning dial had a raised lip on it that was inserted into the clip and it was nicely stuck in place. There is also a very thin wire clip (visible in the picture above) that holds the white plastic strip behind the dial pointer that diffuses the light from dial light. This plastic sheet is also VERY fragile, so remove the clips with great care. I also soaked the metal clips in some Naval Jelly to clean them up. A little soap and water on the white plastic sheet cleans it up nicely. Go VERY gently on the dial glass itself as sometimes water can dissolve the painted markings on the back of the glass. 

So here is the nearly naked chassis. Note the contrast between the covered and exposed areas and the two rust spots - these are pretty easy to clean up with some Naval Jelly that is available in just about every hardware store. Just slather some on, let it sit for a little while, scrub gently with an old toothbrush, and reapply as necessary. After a few applications and a few hours of sitting, the rust should be gone. 

What you will be left with, though, is a bit of a rough surface. I smoothed this area a bit with some fine steel wool. It is important to cover the tube sockets with tape BEFORE you begin cleaning and scrubbing the chassis. Tear lots of little pieces of tape and place them on the socket so the entire socket is covered, but the surrounding metal is exposed. This keeps your cleaning chemicals and resulting dirt slag from getting down into the sockets where it can be very difficult to remove. Some sockets are comprised of layers of phenolic plastic. If liquids and debris gets in between these layers, it will be next to impossible to remove it. Depending on what gets down in there, it might cause a short between tube pins later on when you power it up again. 

So, where to start? I did a total tear-down and refit of just about everything. I am not sure that all of this was necessary in order to make the radio work again, but I figured if I was going to restore it to enjoy listening to it again, I would be thorough with my work. After unsoldering a few wires, I removed the tuning condenser shown above. To clean in up, I just dropped it into some SimpleGreen concentrated cleaner. A few days later, it came out shiny clean!

I did the same for the chassis itself. I bit of the SimpleGreen cleaner (alternatively, WD-40 works just as well) on a small 0000 steel wool pad removed years with or dirt and grime with relative ease. Go slowly, no need to splash it around. You only need enough to wet the pad. Scrub a little, wipe clean with a paper towel and see where things stand. Keep going and you'll have a beautiful, shiny chassis in no time.

New Capacitors:

Next in line for some attention were the electrolytic capacitors, now that the tuner, the dial structure, and the tubes had been removed. These are the components that are most likely to completely deteriorate over time. There are three types of capacitors that were used during this time period: wax paper rolls, wet electrolytics, and mica caps. The first two are the ones that need attention as the mica ones are pretty stable over time.

There are a few good references on this topic, one is a great writeup about identifying and replacing capacitors in old radios and another about replacing wet-electrolytic caps (like those pictured below). Here is another good example of making old wet-electrolytic caps look and work like new.

First a note about capacitors and their values as marked on schematics and the caps themselves:

Waxed paper and electrolytic capacitors are usually specified in units of microFarads. A microFarad is one thousandth of a Farad and is denoted as uF = UF = mF = MF= mfd = MFD.

Mica capacitors (small, brown, solid blocks that look like plastic and often feature colored-coded dots) are usually specified in units of picoFarads. A picoFarad is one millionth of a uF and is denoted as pF = mmF = uuF = MMF = mmfd = MMFD.

In between a pF and a uF is a nanoFarad (nF) which is one thousandth of a uF.

Converting units back and forth is fairly straightforward: 0.001uF = 1nF = 1000pF

The image above shows the only two electrolytic caps in this radio - both of them are part of the power supply that help smooth the recently rectified DC voltage. They contain a coil of metal and insulation that is suspended in an electrolytic fluid that often leaks out and allows the contents to dry out and form a short circuit. Replacing these is the easiest job. Just desolder the wires, make notes of which wires attach where, and then remove them from the chassis. Note the image above shows a cap that has two phenolic insulating washers included (one for above and one for below the metal chassis) for electrical isolation. I used a dremel tool to cut the bottoms off of them (just below the threads) and then cleaned up the outer surface with some of the same Goop you used to clean the wooden cabinet. I made a little hook from a metal coat hanger and used this to remove the old guts from the caps. This took a little while, but eventually it came clean. My original plan was to restuff the empty containers with new caps, but I decided against this (the bottoms were already cut off). Thus, it is just easier to desolder the wires and leave the original cap intact. The nice thing about these caps are their values are conveniently printed right on the barrel. The part number for these caps appears on top (30-2405S) and the electrical value is listed right below (12uF and 350v). Just find a new electrolytic cap of the same capacitance (or somewhat higher - for example it is generally OK to replace an 8-10uF cap with a 10-22uF one, but don't go much higher) and the same or higher voltage rating (NEVER use a lower voltage cap - caps that are subject to over voltage conditions have been known to explode!) and tuck it away for later when you put everything back together. In my case, I used 12uF and 16uF caps rated at 450v to replace the ones shown above. I never did measure these before I cut them apart, so their original condition is unknown. From all of the discussion about how prone these types of caps are to problems over time, I just removed them and cut the bottoms off. The empty cans will go back on the chassis to maintain the original look of the radio. Remember that electrolytic capacitors are polar devices; they have a positive and a negative voltage lead. It is extremely important when replacing wet electrolytic caps that you get the orientation of the new capacitors correct. Most often, the metal can is the negative lead and the center post is the positive lead. Check the schematic to be sure!

The next caps to go after are the paper rolled caps. All of my replacement caps and resistors came from Just Radios - they have tons of stuff available and even sell convenient "kits" of popular resistor and capacitor values. Here is where I made plenty of notes. Make a note of exactly where each leg of the capacitor is soldered. Rolled capacitors like these typically have two leads: an inner foil lead and an outer foil lead. You'll notice in the image below that wax paper caps often have a black band around one end - this band denotes the lead that connects to the outer-most foil. The black band generally connects to the low impedance side of the circuit. It is important that when you place the new film caps into the old cardboard tubes that you get the orientation correct and hook up the new caps in exactly the same orientation that the original caps exhibited. Maintaining proper capacitor orientation helps to keep interference and hum to a minimum. Make a chart, take notes, and make multiple images of each leg of the cap so it is absolutely clear where and how they go back. Follow the schematic diagram as you do this, it will help you begin to understand the circuit. Then, just snip each one out. Don't worry about the rest of the lead that gets left behind for now, you can remove these when you replace the old crumbled rubber coated wires...

This next step was a bit unnecessary for such a common radio, but I wanted to preserve the look of the original caps when the chassis was put back together again. So, I took the old caps, placed them on a sheet of tinfoil, and put them in the oven on low heat (about 200 degrees or so) for about 20-30 minutes. You'll know they are "ready" when your wife complains that the kitchen stinks... The centers of the caps are held in with wax "caps" at each end. With a little heat and a gentle tug with the pliers, the old centers pull right out leaving a nice hollow tube for you to restuff with the new caps. While they are still warm, wipe the cardboard tubes gently with a paper towel to clean them up a little. 

Before you insert the new caps into the old cardboard tubes, you need to determine the proper orientation for your replacement caps. The proper way to connect the outside foil is to the low impedance side of the circuit, which, in the case of coupling caps, will normally be the plate of the previous stage. If it is a bypass cap to ground, connect the outside foil to the grounded side. If it is a bypass cap from a signal to B+, connect the outside foil to B+. The outside foil will act as a shield against electric field coupling into the capacitor, so you want it to have the lowest impedance return path to ground. Randall Aiken explains this well: "Proper orientation of the capacitors will make the amplifier much less susceptible to outside noise, including hum, interference from fluorescent lighting, and tendency towards oscillations or frequency-response peaks and dips due to unwanted feedback from nearby signals within the amplifier, which can affect the tone of the amplifier (and is the reason why some people claim the amp sounds different if the caps are oriented in the opposite way - if there is no accidental coupling, there will be no tonal difference, but there will still be a noise benefit gained from orienting the caps the correct way)."

There are a few ways to locate the outer foil on new film or foil capacitors - each requires different types of test equipment and some basic care for dealing with electricity. We'll handle these in order of increasing complexity. For those of you who are more technically oriented, here is an excellent (though long) video that describes how to determine proper capacitor orientation.

The first way is the easiest: some manufacturers put different length leads on their caps. For Solen caps, the longer lead is connected to the outer foil and should be connected to the negative side or ground. Some manufacturers may use different colored leads - Auricap does this and provides some guidance on their webpage. The black lead on Auricaps should connect to the signal source (for coupling capacitors), to ground (for power supply decoupling), or to the speaker input binding post (for speaker crossovers). Be aware that each manufacturer may have its own convention, so unless you have specific insight provided by the manufacturer of your new caps, you're shooting in the dark and need to use one of the test methods below.

The next method requires access to a signal generator that can create an AC voltage source. Do NOT go anywhere near AC wall outlets for this! Put some AC across the capacitor (connect the cap and a small resistor in series across the signal generator output), and wrap a bit of foil or copper tape around the cap. Then measure voltage from each lead to the foil - no voltage = outer foil, some voltage = inner foil.

The final method requires access to an oscilloscope. You set the scope to it's most sensitive AC setting and connect the cap across the positive and negative leads on one of the probes and grasp the body of the cap with your fingers. Then reverse the cap and repeat. One orientation should result in a larger amplitude waveform (50-60Hz) being displayed on the scope and the opposite orientation should result in a smaller amplitude waveform (or none at all) being displayed on the scope. Whichever orientation has the lower impressed voltage on it has the outer foil connected to the ground lead of your scope. If grasping the capacitor body does not reveal a difference on your scope, put an AC cord that is being used (plug in and turn on a table lamp) against the body of the cap. Read the scope, then swap the scope probe leads. Here is an excellent description of this technique.

Once you have the empty tubes from the original caps all cleaned up and ready to go, align the outer foil of the new caps with the outer foil marking on the cap sleeves, slide the replacement cap into the empty tube, and add a little hot glue to each end to hold things together. Be careful that you match new capacitor values to the label on the outside of the tube. Presto! Brand new caps that look just like the old ones are ready to be re-installed to your refurbished radio! Some people that work on ultra rare and expensive radios will save the original wax and reuse it to seal the ends of the caps again for a more original look under the hood. Cool trick, huh? I measured each of the original caps before I disassembled them and on average, their capacitance measured 50-60% higher than they should - clearly out of tolerance and in need of replacement. You could go one step further to test caps for leakage before replacing them, but I couldn't imagine that after 70+ years they would still function properly. Even if they do (today), there is no guarantee that they will continue to function tomorrow or next week due to their age. In nearly all cases, it is simply easier and safer to replace them, especially because replacement caps of similar physical dimensions are readily available.

New Resistors:

I wasn't sure if the resistors needed to be replaced or not. The only real way to tell is the remove one leg from the circuit and then measure them. I figured since they were being mostly removed, it would be worth while to just replace them as well. Enough resistors to replace all of the original ones doesn't cost more than a few dollars and I'm not really interested in needing to take things apart in another few years because original parts finally broke down and caused a problem. My new resistors also came from Just Radios when I ordered my caps. A note about resistors for tube radios- not all resistors are created equal. You need to make sure that the resistors your choose are capable of handling high voltage (typically in the 350-450 volt range) and high heat conditions.

To replace these, it is easiest to have a parts list and make a list of all of the resistor values (caps, too) and just place a single order for what you need. Then, work methodically between the parts list, the schematic and the chassis diagrams to make sure that you are replacing the old resistor with the proper value new resistor. I pulled the resistors one at a time, measured the old one, identified it on the parts list, matched it to its new replacement, then soldered it in place. Go one at a time and you'll be less likely to screw something up - like putting a new part back in the wrong place. In the end, this step probably didn't need to be performed. Measuring all of the extracted resistors showed that each read about 5% above what it was supposed to. Carbon based resistors from this time period typically came with a 5-10% tolerance window, so the old resistors were still within specification of their original values. Oh well. Now I don't need to worry about them anymore...

New Chassis Wires:

This was perhaps the most challenging and time consuming step in my restoration of this radio. I replaced all of the chassis wire at the same time that I replaced the original resistors, since I had to unsolder each connection point anyhow. The problem with the old wire is that manufacturers used a "new technology" at the time: rubber-coated wires. The "old" standard had been cloth-covered wire. I presume the newfangled rubber wire was less expensive to manufacture and use than the (better) cloth wire, and this chassis was full of rubber wire! The problem with rubber is that after a few decades of heat and exposure to the atmosphere, it dries out and becomes brittle. Once dried/cracked, all you need to do is touch it or move it and the insulation just falls off in large chunks, leaving exposed wire everywhere. This is not good in a chassis that uses 350v power supplies for the tubes!

So, along with my order of capacitors and resistors, I ordered some brand new cloth covered wire in the same set of colors as the original wires. Searching Ebay for "cloth solid core wire" will reveal a number of suppliers. 20 gauge solid core is preferred since it is more rigid and will stay where you put it, rather than flopping around like a wet noodle as stranded wire is prone to doing. If it looks like multiple radio restoration projects might be in your future, order a 50' spool of several colors. Wire color typically has a specific meaning and often follows a long established color convention. This color chart is from the From 1954 RCA Radiotron Designer's Handbook:

The schematic diagram for the radio indicates the color of the wires which is an aid in trouble shooting should the need arise. Determining the color of the original wires is sometimes a bit of a trick because they change over time. The green wires started to look rather blue and the blue wires look a little green, so determining the original color for each wire is not quite as straight forward as it might seem. Things went well replacing wires and resistors until I came the set of wires that ran through the holes in the chassis to the other side and up into the rectangular metal cans on the top of the chassis. These cans are the IF transformers and I took these apart as well. Little screws on the bottom of the chassis hold the cans in place as shown below, the nut has already been removed. 

So, after unsoldering the wires and removing the screws, the metal can comes right off of the chassis. There is a small screw or nut on the top of the can that, after removal, will let you extract the contents. Below are the guts of one of the IF cans. Be VERY careful at this point, some of the wiring here is VERY fine and fragile. I unsoldered the rubber wires, one at a time and reconnected a similar length of new cloth-covered wire and put everything back in the can EXACTLY the way it came out. Watch the orientation of the innards as you put things back. There are often holes in the top of the cans that let you make adjustments. Make sure you document (photos, written notes, etc) the orientation BEFORE you remove the innards so you can put everything back exactly the way it came apart. 

When all of the wires and the resistors have been replaced (and double checked), it is time to reinstall the capacitors. Here is where your carefully recorded notes and photographs are so very valuable. Just work backwards, following you notes, and put the new caps back where they came from.

While everything is apart, this is also an opportune time to spray some contact cleaner into the backside of the on/off switch, the volume control, and the band switch. After doing so, turn the dial back and forth a few times and add a tiny drop of lube to the contacts of the switch so it turns easily without causing too much friction now that it is clean.

New Power Cord and Plug:

The original power cord on this radio was replaced sometime in the past with a cheap looking plastic-coated lamp cord -this is typically called "zip cord." The original cord was likely cloth-covered and long since frayed to the point where it was a fire hazard. The newer plastic cord didn't seem right to me, so I found some "Vintage Lamp Cord" on Ebay that looks nice. Ten or twenty dollars will get you all of the cord you need, often with a period-looking plug at the end.

If you desire a fancy plug, there are plenty of these available, too. Another search on "vintage lamp acorn plug" will reveal a treasure trove of nice looking plugs for $5-10. Be sure to pick one that is polarized so you can add a proper fuse to the chassis. The end of the AC wire needs to be tied with an "Underwriter's Knot" before the wire leads are attached to the screw terminals inside the plug. This prevents stress on the cord from tugging at the wire termination. 

Reassembly:

Now that all of the original resistors, capacitors, and crumbling wire has been replaced, it is time to begin putting everything back in place on the top side of the chassis. I found a source for original new-old-stock (NOS) dial cord and springs on EBay. Dial cord needs to be a very specific type of cord, a typical woven cotton or nylon string will stretch over time to the point where it won't work any more. The spring keeps tension on the cord to prevent it from slipping while turning the tuning knob. The original schematic or service information for your radio will typically also include the directions for restringing the dial cord and pointer. This is sometimes difficult to figure out even WITH the proper diagram... A small drop of super glue or nail polish on the knot at the end of the tension spring will keep knot from slipping over time once you finally get it right. A very kind soul on the Philco Phorum donated a dial pointer to my project as well.

Here is a good resource for stringing dial cord for a number of radios, each is quite different than the others.

The push button tuning mechanism was also a bit gummy and sticky after sitting unused for several decades. Note the black in the image below. I used some typical electronic contact cleaner to remove the gunk and then a few squirts of WD-40 re-lube the mechanism so that it works as it should. 

Before and After Electrical Refit:

OK, so here is the before and after of the underside of the chassis. All of the resistors, capacitors, and rubber wire have been replaced. It has been fitted with a new cloth covered power cord, a proper period AC plug, and I added a 1A fuse to the power supply line before the power switch as an added safety measure. Overall, the appearance hasn't changed all that much, it just looks cleaner!

The before picture is above and the after picture is below. 

The only obvious differences are the new cloth-covered power cord, two new electrolytic caps, and the protective fuse.

All Clean Again:

Here it is, all put back together again and ready for the first power up.

First Power Up:

Using the protocol I described above to power up the radio revealed a working transformer, but a dead rectifier tube. This tube showed connectivity among ALL of the pins - not a good sign at all. Fortunately, a NOS rectifier only cost $10 on ebay. After replacing the rectifier and trying again, things were much better! The heaters on the rest of the tubes began to glow and I could measure 250v or so at the plates of rectifier. One step forward, but the problem now was lots of hum and buzzing from the radio. I could just barely tune in one station, but it was VERY faint. What a disappointment after all of this work!

This is the place where you go back to your original wiring notes, photographs, and schematics. Double check EVERYTHING. Trace every wire, every resistor, every capacitor. Everything! A few minutes of this revealed that I reinstalled one of my new capacitors incorrectly. Oooops. It belonged on the tube pin adjacent to where it was actually connected. Of all of the types of errors that I could have made, this was the best possible one. Capacitors prevent the flow of DC currents, so putting one on the wrong tube pin actually just prevented the radio from working properly without causing new damage by allowing current to flow where it didn't belong. Pfew - I got lucky on that one! Put a resistor or wire back in the wrong place and you'll likely have fireworks and damaged parts!

One more power up was all it needed - my 1939 radio worked again! What a thrill to take a nearly century old piece of equipment and listen to it again!

Ta-da! All done and looking/functioning better than most people born in 1939 that I know.

Imagine the events that this radio brought into someone's home since 1939: FDR's unprecedented third and fourth term elections as President of the United States, the beginning and end of World War II, the first moon landing, etc ... What a great piece of history! All together, new parts and other misc supplies probably cost somewhere near $150 for this restoration project. The re-wire portion of the project took the longest amount of time. All in all, it was about one year of sporadic work. The key is to take your time, carefully document EVERYTHING, and work methodically.