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Some helpful information, tips and suggestions for the novice, beginning technician and sometimes the experienced
is offered here. Keep in mind the electrical information provided is
in the form of suggestions, not intended to be advice or specific
instructions. The electrical circuitry in radios and electronic
equipment can be dangerous and even fatal if certain safety
precautions are not followed.
Use your browser program's Find feature (edit; find) to search for subjects on this page.
This is something I've been thinking of offering for some time now as I have been learning and developing my skills, abilities and knowledge for more than 50 years. Much was learned on my own, some from others along the way. So on this page I'll share these (for what they are worth) with those that are interested. I do not claim to have all the answers or imply that I know it all or the ultimate expert. Some may disagree with my procedures and methods. What I offer is what has worked for me and some of what I suggest may be considered novel. New tips will be added as time permits. Those of you that wish to contribute, feel free to contact me with your tips and if used, I'll give appropriate credit.
Some of these tips require some basic knowledge of electronics to understand. In order to service or repair something properly, you not only need to have certain skills with your hands, but you must first understand how it works.
With electronics, like any other technical field, it takes years to become a properly skilled technician whether it's with old radios or modern technology. There is no crash course that will make you a overnight expert. There are many out there that learn about the basic things that fail most often (like the electrolytic capacitors and other capacitors that are constructed from paper and foil). Replacing these items will often bring the radio back to life but beyond that if the radio fails to work properly, they are lost as they do not know how to troubleshoot. I call these guys memory technicians or electronic mechanics. Without an understanding of electronics or how something works, it's impossible to trouble shoot a serious problem. So I suggest to these folks; find an old course in basic electronics and radio repair, study it, learn the theory of how a radio works. It's not that hard and very rewarding when the time comes to repair, restore or troubleshoot a problem.
If you are seriously interested in learning about radio, I would start at the beginning and first learn basic electricity, then basic electronics. Afterwards you should find an old vintage course that deals with tube technology and radio repair. As stated above, many of the tips I give require a basic understanding of electronics. So if you don't understand basic electronics, please don't ask me to explain. For the non theoretical issues, feel free to ask if you have questions.
This is a new endeavor and I will be adding subjects as time permits. As this page grows, I'll categorize and alphabetize them. Other than the first 2 or 3 tips, the subjects are not in any particular order.
Tip #1 Always do this first!
This first tip is so simple, yet extremely important and in my opinion the most valuable. It's usually not included in most courses in electronics. I learned this very early as an apprentice TV repairman at the age of 15 from Jake Rodman (Supreme Radio & TV service), a first class TV technician in my home town of Ashland, KY,:
Always give the piece you are about to service a good visual inspection. Give it serious scrutiny, not just a glance or quick once over. Be diligent, give the piece (or pieces) a good cleaning, look between the components, the tuning condenser, remove the tubes, inspect the sockets. Look on the underside for sloppy workmanship done by a previous technician or mechanic (this is often the source of many problems). A great deal can be leaned by noticing the physical condition of the chassis. For example; a burned resistor, blown-out capacitor, sloppy soldering, a bundle of wires all globed together by the previous mechanic who just clipped off & left the leads & wires of previous replaced components. Look for material leaking & oozing from a transformer or canned component. Notice anything that looks out of place.
Tip #2 SAFETY ON THE REPAIR BENCH!
Always use an isolation transformer when working on an AC/DC radio or television (sets without a power transformer). Failure to do so can result in a serious electric shock plus damage to your test equipment when you hook up the ground lead to a "hot" chassis.
DO NOT plug your test equipment into the isolation transformer, just the radio. I've seen folks wire their isolation transformer to a plug strip with all their equipment plugged into it and wonder why their "scope's" ground lead went up in smoke when they connected it to the radio chassis. If all your equipment is plugged into the isolation transformer, then nothing is "isolated"! Only the radio (or television) under test should be plugged into the isolation transformer!
Tip #3 Line Cord Polarity! THIS IS AN IMPORTANT SAFETY ISSUE!
You will likely encounter a shock on any series strung (AC/DC) tube radio if you happen to have one hand on the chassis and the other hand (or your feet) coming in contact with a ground source. All AC/DC radios the chassis is connected to one side the line AC line either directly or by a capacitor/resistor. In the case of the type that is connected by a capacitor network the shock is normal and not deadly unless the capacitor is shorted. You can get a deadly shock if the "HOT" side of the line cord is connected directly to the chassis as some early radios were!. Visually check the wiring, that's the best way to tell if one side of the line cord goes to the chassis (usually via the AC switch). Some AC/DC radios have a floating ground (or B-), that is the AC line is not connected to the chassis directly. This (ground bus or common return) floats above the chassis but is electrically connected to the chassis by a resistor and capacitor in parallel. No matter which side of the chassis the line cord connects to, you can still get a shock because the o/o switch will determine which way the chassis comes to the line cord potential (on, one side off, the other) Some of those sets were deadly as one side of the cord was tied directly to the chassis and in the 1930s and well into the '40s there was no such thing as a polarized AC plug. Getting a minor shock from a chassis that is not directly connected to the AC line (as stated before) is normal but not a real hazard as the current is quite low through the (normally); 270K - 330K resistor.
The only safe way to prevent a shock is to make wiring changes to the AC wiring so the neutral side of the line cord is always connected (with a polarized line cord & plug) directly to the chassis (or common if it's floating above chassis potential). You'll need to re-wire he AC line so the "hot" side goes to the switch, the neutral side to the chassis or common return bus. This way the neutral or ground is always at the chassis or "common" potential and you wont get shocked (as long as the polarized plug is plugged into a correctly wired socket). You will have to alter the chassis AC wiring so you are switching the "hot" side of the AC line into the circuitry and not the chassis or "common" to neutral (or ground).
When working on these AC/DC series strung chassis's (no power transformer), always use an isolation transformer to prevent electrical shock or destroying your test equipment. Plug only the radio into the transformer, not your test equipment. If both are plugged into the transformer, your equipment can still be damaged depending on it's polarity with respect to the radio chassis.
Tip #3A - Dealing with resistance line cords. I have a separate page for this issue,
Tip #4 DON'T .......PLUG THAT OLD RADIO IN!! Click here for this tip.
Tip #5 SAFETY!
Never stick both hands into a live radio or TV cabinet or the chassis. Always disconnect the power cord, don't just rely on the on/off switch to turn off the power. Discharge the high voltage in a TV set before handling the CRT or HV components. Do it several times as sometimes in some early TV's the CRT will retain high voltage and recharge itself several times after being discharged. This is because it was not fully discharged the first or second time due to internal resistance of the anode.
Tip #6 Cleaning old wood radio cabinets
If it's really, really dirty, first remove the insides (chassis). Then vacuum and clean it with care. The procedure to use will depend on what it's contaminated with. If it's just household dust, a powerful vacuum cleaner (with crevice tool attachment) and small, stiff paint brush is all that's needed. If it's caked with rust, crud and or rodent debris, that's a more serious matter. For normal cleaning, the cabinet should first be wiped down with a cloth quite damp with household ammonia diluted with water (about 50/50) being careful not allow the liquid to soak into the wood. This will get rid of the water soluble contaminates. Then wipe dry and clean again with paint thinner or cigarette lighter fluid (NOT LACQUER THINNER!). When dry, wipe it real good with Scots "Liquid Gold", Lemon Oil or some other high quality product that will soak into the wood. Allow to soak in for 15 - 20 minutes hen wipe down and use a good furniture polish such as "Oz". Sometimes this is all that's needed.
If the finish is not satisfactory, looks dull or maybe has been sun bleached, Treat the finish with "Mar-A-Way" (a product I use). After using according to the directions, finish the job with a good furniture polish.
Tip #7 More on wood radio cabinet issues
If after doing as I suggest above and there are minor flaws, scars and surface scratches that show, here's how to make the cabinet look better without a re-finish job.
Minor sun bleaching and surface scratches (scratches that have not penetrated into the wood).
1st, I would treat the finish with "Mar-A-Way" (a product I use). After using according to directions apply a good furniture polish. If there are still scratches that penetrate into the wood, you can use a felt tipped pen to blend the colors. These pens come in a variety of colors and there are a number of brands on the market. Not all of these brands work all that good. The two best I have found are the "Mohawk" brand, second best is the "Scratch Fix" pens from the Miller company. Don't waste you money on the "Minwax" brand, I find theirs to be inferior. Keep in mind, scratches that go through the finish into the wood, can be somewhat made to look better but won't go away without the efforts and expertise of a wood re-finisher or finish repair. Finish repair is very specialized art.
2nd, If after doing the above and still not satisfactory, an "amalgam" can be tried. I make my own by mixing equal parts of Gum Turpentine and Boiled Linseed oil. This is best applied in small areas (4 - 6" square) using "0000" steel wool, soaked with the "amalgam", rubbing in a circular fashion. Do a section at a time until the entire surface is done and wipe down after about 20 passes for each section. When all done then repeat the process with a soft cloth. Then do the same again, this time with long strokes across the entire surface following the grain pattern.
Once you are pleased with the results, then apply a good furniture polish such as "Oz".
3rd, If step 1 & 2 does not offer satisfaction, then strip and refinish will be required.
Crazing (the finish is alligator'd but still intact). Treat as suggested in step 2 (above). Many collators prefer an original alligator'd finish over a refinish.
Tip #8 Faux finishes
Many radios of the 1930s & '40s was lacquer over a “photo finish”. What I have done with those faux finishes that have dulled but still pretty much intact is to clean good with Naphtha, paint thinner or Cigarette lighter fluid (DO NOT USE LACQUER THINNER, ALCOHOL OR ACETONE!). Wipe it down and let dry, then give it 6 or 8 lights coats of lacquer. Rub lightly between coats with 0000 steel wool. After final coat of lacquer, rub it out with a good deluxing compound or make your own deluxing rub with a linseed oil soaked soft cloth and dabbed periodically in rottenstone powder.
Tip #9 determining capacitor voltage ratings, paper or electrolytic.
Many of the old schematics did not include the voltage values. It's pretty easy to determine the voltage ratings by the type of power supply.
If it's a power transformer'd unit, then go with 450 volts for the filters in most cases. However some very early AC radios, the original capacitors may be rated as high as 600 volts. Sometimes they were overrated but to be sure, monitor the B+ at the output of the rectifier tube and use a capacitor at least as high as the highest voltage your meter displays during warm up.
A point of mention, the filter capacitors used in the early AC sets that were packaged in large metal containers (usually rectangular or square) were not the electrolytic type. There were paper capacitors, usually no more than 8 uf (often much lower like 1-2 uf) capacity. Unless the power supply exhibits hum, low voltage or shows excessive potting material leaking from the cans, it's not necessarily a good practice to just replace them. These condensers can exhibit a bit of leakage above 250K is no big deal but in the power supply. If you do replace them you can use electrolytics but polarity must always be observed even though the original were non-polarized, not so with non-electrolytics. Be sure and stick with the original capacity values as using higher value may result in more (not less) hum do the the fact that the capacitor value and the choke (a reactor) result in a tuned circuit.
For coupling and capacitors used in the plate or screen circuits go with capacitors rated 400 - 600 volts. It does not hurt to stick with 600 volts caps in those circuits. For cathode bypass circuits, a 200 volt rating is plenty, since these capacitors tend to be larger in capacity, using 600 volt caps simply take up more room and are more expensive. It does not hurt to overvalue the voltage rating a bit, but never under rate them.
If the radio has series strung heaters (no power transformer), then 150 - 160 volts is the typical rating of the filter caps, coupling & B+ by-pass should be at least 200 volts. I would still recommend 400 - 600 volts for these as the lower voltage capacitors are hard to find in new stock (they are usually rated at 630 volts).
Most new old stock paper capacitors will be leaky and I would not recommend using them unless you have good capacitor checker that will apply full rated voltage to test for leakage.
Tip #10 Testing capacitors (can you check 'em in circuit?)
Some use an ohmmeter to check capacitors. This test will certainly reveal a dead shorted capacitor, it will not tell you if one is breaking down under voltage.
"In circuit" capacitor checkers have limited reliability and usage as you cannot check for leakage with such and instrument. To check for leakage requires applying the operating voltage, the Heath IM-11 or IT-28 can apply up to 600 volts to the capacitor being tested. You can only do this with one end of the capacitor disconnected.
So the answer is you can only check for capacitance with an "in circuit" checker. Most problems with capacitors is due to leakage current caused by a breakdown of the capacitor's dielectric. Such leaky capacitors will often pass with flying colors a "capacitance" check as they only break down when the operating voltage is applied.
I use and recommend the Heath IM-11 or IT-28 and the Sencore LC53 "Z Meter". If you want a more serious analyzer, I would recommend any of the Sprague "Tel-O-Mike" units that have been restored and calibrated.
Tip #11 Removing the potting material from transformer & capacitor cans (the black* stuff that looks like pitch or tar)
Remove the container from the chassis and place it in the freezer over night. The potting material will become very brittle and you can bang around on the can and often the entire contents will just fall out. For the more stubborn ones, you can tap or chip the stuff away with a screwdriver until it's loose enough that the whole insides can be dumped. Be careful and don't gouge to deep in the can as you may damage good components such as a transformer or choke. Do it outside or over a garbage can, that stuff will get on your floor and shoes and if you think getting the stuff out of the can was a problem, you have an even bigger one removing it from you carpet. When you tap on the can use a wood block between the hammer and can so you don't ding up the container.
* There are different materials used for "potting" components as well as other colors. Some have fairly low melting point such as "Pine Pitch" which is amber in color. This can be melted with a heat gun, saved and reused. Another type of material used for potting is wax, it too ca be melted and re-used.
Tip #12 Early radio antenna & volume control problems
Early radio receivers made from the early 1920's to mid 1930's work a bit different than later radio sets. All required a "long wire" antenna and few during that period had "automatic volume control". In the early days a typical radio installation required an antenna strung up outside on poles or from the house roof-top to a barn, tree or pole of some kind. Radio stations during the 1920's & early 30's where often far away and to receive them, the higher and longer the antenna, the better. A typical antenna installation was about 100' long for good reception of distant stations.
If there was a local station in your area, this was another problem because unlike modern radios (or those made after the mid 1930's), there was no "automatic volume control". This meant a strong local station would boom in, usually overloading the radio often to the point that you could not turn down the volume. The solution to this was to remove the antenna altogether or shorten it substantially. This is still problem today when operating some vintage radios. You'll find local stations will "boom" in at very loud volume and more distant stations require advancement of the volume control. This is normal for this early technology. These days with so many local stations a wire 15 -20' long lying on the floor or stuffed out of sight between your carpet and base board will allow you to pick-up local stations.
If you have an attic, a wire strung up there will work just fine for distant reception. Another option is to purchase a modern devise called an active antenna, it uses a telescoping rod and has an amplifier built into the base that works as a "long wire" antenna. I have not used such a devise but see them advertised (I believe Radio Shack had them at one time and may still). I have heard positive feedback from those that have used them.
Tip #13 Automatic Volume Control (AVC) what does this mean?
In the early days of Radio (early 20's - mid 30's), radio receivers did not have "Automatic Volume Control". So when tuning one of these radio sets a strong local station would come with loud, often with uncontrollable volume. Then if you wanted to listen to a weak distant station, you had to first turned up the volume, sometimes to it's maximum setting. If you forgot to turn the volume down when tuning back to your local station, your speaker might want to "jump out of it's cabinet".
This problem was solved by improvements in the tuning circuits and the addition of a circuit called AVC (automatic volume control) or AGC (automatic gain control). This provided a fairly even volume level throughout the tuning range. Extremely weak stations, however would still require an increase in manual volume control as AVC operated within a certain parameters and it's function would drop out when the signal dropped below a certain level.
Tip #14 Testing Vacuum tubes
is there and "NOS" test? < click
Tip #15 Checking your Phono amp & cartridge.
Here's a simple test to determine whether a no (or weak) sound is the electronics or your cartridge.
Lift up the tone arm so you can view the underside, locate the two small wires that connect to the cartridge holder and make sure they are connected to the holder.
Then turn on the unit and turn the volume up to listening level and with a small screwdriver of other small, narrow metallic object such as a nut pick, while holding this object in one hand (the arm is metal so don't hold the arm with your other hand or this test may not work) touch each wire connection to the cartridge holder (one at a time and don't short them together and not to worry, you won't get shocked). If the amplifier's electronics is working, you should get a loud hum when touching one of these wires. This loud hum should increase and decrease in volume level when the volume control is turned up or down, it should be quite loud at the high volume setting.
If you get only a weak or slight sound, chances are the phono's amplifier is not working and you will not hear any controllable sound from the stylus. If you hear the hum I described, either the cartridge is defective or there is a contact or wiring problem to the electronic amplifier.
Tip #16 Noise or sound "cut out" when tuning in stations
The problem with noise and static when you tune can be caused by one of 3 things:
1) Dirty wiper contacts between the rotor plates and shaft (this is the small metal clip that makes contact with the rotating shaft of the tuning condenser and frame right in the middle of the tuning condenser, it will have two (or more) of these depending on the radio.
2) The plates of the tuning condenser may be bent and contact is occurring between the movable and stationary plates.
3) "crystal whiskers" may have grown between the plates on the tuning condenser. These are difficult to remove, you can determine this by using a loupe or magnifying glass and take a close look at the condenser. If this is the case I can give you instructions on how to deal with this problem. I'll publish more info on "crystal whiskers" later.
Tip #17 Cleaning noisy controls, poor or open switch contacts
These problem can usually be corrected with "Craig DeoxIT D5" if applied properly.
DeoxIT D5 is very effective but a bit expensive, so don't waste it by bathing your switch or control in it, it is not meant to be used a washing agent. Using to much can be detrimental as the residue will attach contaminates and can create a short or have a semiconductor effect. It works best with a tiny amount placed in the proper place. Many controls and switches have internal access if you know where to look. Many are sealed and in order to clean them you must either take 'em apart or carefully drill a tiny hole so you can squirt a whiff of "DeoxIT" inside. One must be very careful when drilling the hole because if you don't, you'll ruin the control or switch.
Here's how I do it:
Start by using the tip of a hypodermic needle (.027" OD). Break it off of the syringe fitting and file the sharp end blunt so you don't stick yourself. Then force one end into the plastic tube that comes with the "DeoxIT".
Now you have tip that will fit into tiny areas. View the image I've created so you can see the areas where the "DeoxIT" can be squirted (remember use a very small quick squirt). Once your sure you've got the stuff inside the control or switch, work the control throughout it's rotation a few times and work the switch on & off 10 - 12 times. I've found that unless the contacts are broken, burnt or damaged, this method will restore proper operation. A good switch should measure "0" ohms (in the on position) if working properly.
With toggle switches, place the switch so the toggle is straight up and give it a squirt downward so it gets into the bottom of the switch (where the electrical contacts are). Then toggle it 12 - 15 times.
After you have successfully restored the switch to proper operation, I suggest you then blow I out with a few squirts of canned air to remove any excess "DeoxIT".
Tip #18 SOLID STATE REPLACEMENTS FOR HICKOK TUBE TESTER'S TUBES?
Click here for this tip.
You have a wood radio cabinet which could be real wood, wood veneer or a "Faux" or "Photo Finish". It looks pretty good but want to make it look better without re-finishing it - What To Do -
First, give it a good cleaning. There are usually two types of crud on an old radio cabinet; (1) greasy, waxy stuff from household contaminate, candles, dirty oily fingers etc. (2) foodstuffs (again from dirty fingers, kids or just plain slobs). Different cleaners are required as one wont have much of an effect on the other. Here's what I have found that works very well:
(1) Clean off the water soluble stuff with a damp (not soaking wet) cloth with an ammonia based cleaner. This works on the foodstuff contamination (the remains of the peanut butter & jelly sandwich for example). Be careful not to get the surface too wet, you don't want to let the cleaner soak into the wood.
(2) Then for the waxy, greasy film, I've found that cigarette lighter fluid (or paint thinner) works best on this household stuff that has accumulated over the years. Whatever you do, DO NOT USE LACQUER THINNER! (It will dissolve the finish). Wet # 0000 steel wool with the paint thinner or cigarette lighter fluid and give it a good rubbing, going with the grain (careful not to rub off the finish). Do this until it looks nice an clean, then wipe it down with the fluid. If the finish looks good at this point, go to step #3. If the finish is discolored, has minor surface scratches, or irregular or blotched color, I recommend and use "Mar-A-Way". It can be purchased from the distributor in Portland, Hoch & Selby just off Sandy Blvd on 25th Ave. Scratches that go through the finish will not be corrected by using Mar-A-Way.
(3) After you get it clean and smooth, touch up any remaining scratches with a felt tipped staining pen of the correct color. I recommend and use either the "Miller" or "Mohawk" brand felt tip touch-up staining pens, they come in a variety of colors. I've tried the Minwax" brand with disappointing results. Now, if the original finish is intact, go to step #5. Only do step #4 If the finish is worn into the wood.
(4) Now give the treated area several coats of lacquer (I prefer Deft), steel wool it again (no more cigarette lighter fluid) then clean (to remove the dust particles) now a few more coats of lacquer and give it a final steel wool rub down. Clean it real good and do step #5.
(5) The finish will now look too glossy (or dull if your just completed step #3). Now here's the real secret of restoring it back to an original looking finish. Rub the entire cabinet with a "Deluxing " compound. You can find such a product under the Mohawk or Behlen brands at most woodworkers suppliers. A good rubbing with these product will give amazing results and well worth the time and "elbow grease". If you can't find a deluxing rub, make your own by using rottenstone wetted with lemon oil.
Closing note, step five should always be done on any newly painted or refinished cabinet for that original finish look. Not doing so will give it that just painted or obvious refinished look.
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Tip #19A Refinishing of a wood radio cabinet
Clean and strip the old finish, make any necessary cabinet repairs. Then sand it all out smooth with 600 grit as your final sanding effort.
Now you are ready for grain filling and staining. I prefer an oil based combination grain filler and stain. I've found the best of these products from Constantine's Wood Center.
After the grain filling and staining are complete, finish the job with Deft (the brand of lacquer I prefer) using multiple coats and rubbing with # 0000 steel wool between 2 or 3 light coats. Let the lacquer dry for about 30 minutes to an hour (depending on temp & humidity) be careful not to cut into the wood with the steel wool, just smooth out any dust specs and overspray. After 3 - 4 of these applications as suggested above, do one final rubbing with #0000 steel wool.
Now a final rubbing with a deluxing rub (as noted in the above "spiffing" article). If you can't find a deluxing rubbing compound, make your own with "Rottenstone" and Linseed oil. Wet a cloth with the Linseed oil and sprinkle the wetted cloth with the rottenstone powder. After a good rubbing, wipe away any reside left by the rottenstone with lemon oil polish and dry. Do this until you get the finish you desire. When done, the finish should be shiny and the grain lines should be level with the finish. The finish on nearly all wood cabinet radios made in the late 1920s on had a high gloss finish, no grain line depressions or a dull oiled finish as some seem to prefer.
Tip #20 old style spaghetti, make your own
When restoring old battery radios (and some early AC sets) of the 20's you'll often need the old style lacquered spaghetti which can be difficult (if not impossible) to find.
When it comes to the old style spaghetti, you can make your own
How to make replica old style Spaghetti.
(1) Find some of the old style cloth shoe strings (they are too are getting hard to find). These old shoestrings look flat but are really tubular (hollow inside, pressed flat).
(2) If they (the shoestrings) are not the color you want, you can dye (the white ones) to the desired color.
(3) Cut the shoestrings to the desire length and slip a piece of straight, solid wire through the center. Old wire coat hangers work well (again, may be hard to find these days). Stretch it out over the wire and let dry.
(4) When dry, carefully remove the dyed cloth from the wire and give the wire a good coat of *wax and slip the cloth back over the wire (being careful not to get any wax on the outer surface of the cloth).
(5) Now give the stretched out wire a number of coats of clear lacquer. When the desire number of coats have been applied and dried, you have a good replica of the old style spaghetti.
* The waxed wire will keep the lacquer that penetrates through the wire from working as an adhesive. When dry, you have a good replica of the old style spaghetti.
When traveling the old highways and back roads and you find an old general store (or hardware store), it pays to stop an look around. Some of these old stores will have inventory that can't be found anywhere else. I've found and stocked up on old shoestrings and other hardware from some of these places.
Tip #21 Repair & Refinish broken Bakelite & Composition panels and cabinets.
First remove all the hardware from the panels (and pieces) and wash and clean them (do not submerge in water or use a heavy detergent with ammonia or alkali's). Wash them like you would a Bakelite panel (see my article on cleaning Bakelite on my web site).
Before heating, place the pieces between two flat pieces of thick aluminum (any kind of metal at least 1/4" thick will work) with a weight on top so the heated the panels will flatten out as they heat up. Leave in the oven about set for about 200 degrees for about 20 minutes. Turn off the heat and let them cool, they will now be nice and flat.
Using a filler epoxy such as JB weld (the gray stuff, don't use the clear stuff as it does not get hard enough). Fill the areas were they were broken, clamp in place and let the epoxy cure (don't use the 4 minute stuff, you need more working time). Fill any gaps were pieces may be missing, smooth and trim any excess epoxy before it cures. After at least 48 hours (a week would be best because you want the epoxy as hard as it can get before final sanding and surface prep) you will be ready for finish preparation.
PREP THE SURFACE:
Now sand the surface areas making sure all are smooth so there are no ridges or bumps or gaps. If the original panels had a brushed texture (many do as did mine), sand as much as you can straight up and down and not cross ways or diagonally. If done right, the final sanding will leave the panels slightly with a brushed texture so the final finish will look original. If there are air gaps, holes etc, apply more of the epoxy, let it cure and repeat the process until all is smooth.
After you have the panels smooth, textured (if needed), you are now ready for the finish. First seal with a lacquer sanding sealer and sand it lightly remembering to sand in the brushed texture (if desired). Wash off the dust and apply a couple of coats of black gloss or semi-gloss lacquer. Rub out between each to of two three coats until you have applied at least 6 - 8 (or more) applications depending on how much rubbing and sanding is done between applications.
When all done and you are satisfied with the appearance, give it a final rub out with a deluxing compound. If you can't find a deluxing compound, make your own by using Linseed oil and rottenstone. This last step applies to any refinish job and is usually not done by most. If not done it will look like you have just refinished it, if done right it will look original.
If you've ever hooked up an old horn or other early (1920's) radio speaker to a modern radio or amplifier, you have undoubtedly found it works very poorly, producing weak or no sound.
Most all the 1920's radio speakers were high impedance while nearly all modern speakers (those made from the early 1930's on) are low impedance. Most high impendence speakers are around 2000 ohms. Modern ones are usually 4 -16 ohms (quite a mismatch if the wrong speaker is connected to the wrong output). Most tube type amplifiers made from the 1950's on offered a range of output impedances but none high enough for a proper match to the early speakers.
Its quite easy; to match your modern amp (or radio) to a vintage horn or disc radio speaker, just use a common audio output transformer connecting the *primary side to the vintage speaker and the *secondary to your radio or amp's output. If you wish to connect a vintage radio to a modern speaker, just do the reverse (*primary to the radio, *secondary to speaker). If your vintage speaker is in good working order, you'll find this will work just fine. Make sure the transformer you plan to use is designed for tube applications. One made for transistor circuits will not work.
* If you are not a technical person and can't tell the primary from the secondary, here's a couple of tips: The primary side is usually color coded with cloth, rubber or plastic insulated wires that are red and blue. The secondary is often **bare wires or if insulated, green & black are the usual colors.
** not really bare but insulated with an enamel coating.
If you still cant determine which way is correct and you don't have an ohmmeter (or know how to use one), try it each way. There's no harm if you get it wrong, just keep the volume level at a low level until you hear sound.
Tip #23 Pot Metal <<< click on link
Tip #24 Over Heating of Power Transformers and black stuff oozing from potted containers.
It's not normal for the potting material (usually PCB) to ooze from the cans of the power transformers or other components (canned capacitors or chokes). However, it's not uncommon to see some of this residue around the chassis area on some of these early sets. The discharge was probably caused somewhere in the past by overheating due to a circuit problem or over voltage. The power transformers use in many of the pre-1940 radios etc were designed to operate at 110 volts. Most all of the pre-1930's sets were made for 110 volt AC line voltage operation. Some had a switch to select the appropriate voltage such as the Radiola 17 & 18.
It is very important to determine the actual line voltage provided in your area and take necessary steps that you don't operate your radio with too much line voltage. The line voltage has been slowly creeping up and in many areas today it exceeds 120 volts (it's 121 in my area). This small increase does not affect most modern electronics because of the modern regulated power supplies (many will operate from around 90 to 240 volts). This voltage increase will result in a significant operating voltage increase in the power supply of these early radios including the filament voltage of the tubes. Increasing just the filament voltage of the tubes will not only shorten the tubes life and overheat the tube but increase the heat factor of the entire radio. - THIS IS NOT GOOD!
Tip #25 make my new reprint labels look aged
My reprint labels will look like newly printed with all blemishes and defects removed. The best ay to make 'em look old is to stain them with coffee, tea. Since they are laser printed, doing this will only stain the paper, the print and graphics will not be affected by a water based liquid. DO NOT USE SOLVENTS OR SOLVENT BASED STAIN as they will most definitely will affect the print and the graphics. Allow to dry on a flat surface after staining with coffee or tea.
Tip #26 measuring voltage of an early radio
Many of you may not be aware that the voltages shown on the schematics of old radios were likely not taken with a vacuum tube voltmeter, some of the meters used had an OPV (OMHS-PER-VOLT) rating of 1000! Some schematics will specify what what was used for the measurements but many did not. This is significant when measuring using a VTVM or more modern digital VOM as you will measure a higher voltage than specified on the schematic. You can do the math and figure the resistance needed to be in parallel your meter, examples:
To simulate 1000 OPV,
10 volt scale, 10K/1 watt
50 volt scale, 50K/1 watt
250 volt scale, 250K/1 watt
500 volt scale, 500K/1 watt
Tip #27 Replacing capacitors in early Radiola (and other brands) of AC radios
My attitude concerning the wholesale replacement of the "potted" power supply capacitors in the early AC radios; DON'T, unless there’s reason for doing so. Over the years I have restored many Radiola 17s, 18s, 33s, and ‘60s and not one of them needed the power supply filter capacitors replaced. I’m not stating that they can’t fail, but unless there are symptoms of failure (low voltage, hum etc.) leave ‘em alone. They are not electrolytics, they are large, rugged paper & foil capacitors.
Now as for the by-pass and coupling capacitors (and other small paper foil types) used in other circuits, those are almost always quite leaky and I recommend replacing by re-stuffing the original cans (if so enclosed) with modern capacitor’s. If the radio does use any electrolytic types, YES, replace 'em.
© C.E. Clutter