By Doug Criner

I'm told that to qualify as a genuine "antique," an object must be at least 100 years old.  Therefore, there are presently no truly antique radios, only vintage or old radios.

Old tube-type radios are interesting pieces of historic technology and style.  Many people collect them.  Me?  I mainly enjoy fixing them, keeping them working, and giving them away to friends that will appreciate them.  Many old sets are nice furniture pieces.

Tube-type radios are available at flea markets, antique malls, garage sales, and on eBay.  I have about 20 old radios, buying perhaps two-thirds of them on eBay.  Of those from eBay, about half were received in the condition I expected, a fourth were disappointing, and a fourth were nicer than I expected.  Most of the sets were non-working when I purchased them.  Fixing the electronics is more fun and easier than refinishing wood cabinets, finding missing knobs, etc.

Why tubes?  Tube-type radios are of historic value and usually have a very good sound.  They are very easy to work on, at least compared to modern solid-state electronics.  The wiring is point-to-point, not robot-assembled printed circuit boards or integrated circuits.

Firestone Model S-7403-9 (8 tubes, Ingraham cabinet), c. 1940

The above photo shows a recently acquired table model radio, purchased in non-working condition on eBay for $42, plus $21 shipping--$63 total.  It is almost all original, including knobs, pushbuttons, cabinet back, built-in antenna, etc.  Work performed included:  replacing the rectifier tube, recapping, light cleaning, reattaching a sagging grille cloth, replacing the power cord, and wiping the cabinet with antique restorer.  It works on all three bands (standard AM broadcast and two shortwave bands), the pushbuttons work but tend to stick in, and the set has deep rich tone provided by a large speaker.  The cabinet certainly isn't perfect, but it displays well.  Of the eight tubes, four are the original Firestone brand.  The four control knobs are:  power/volume, tone, band selector, and tuning.  Like most Firestone sets, this one was built by Stewart-Warner.

But Read This!

A disadvantage of vacuum tubes is that they operate at high voltages, 180-400 V DC for a typical receiver.  Transistors typically operate at just a few volts.  Both tube- and transistor-type radios have a 120-V AC supply, which itself is hazardous.  (Many places outside North America use 220-V AC, which is even more dangerous.)

The higher voltage used by tubes causes stress on various components, including capacitors.  For this reason, old radios should be “recapped” with modern capacitors of appropriate voltage rating.

Tube-type radios present a significant shock hazard—the usual AC supply, but also the high-voltage B+ DC plate supply.  To demonstrate the hazard, charge a 40-μF electrolytic capacitor across the B+, and notice the fat, cracking spark.  Now short the terminals of the same cap, and observe the same dissipation of energy.  (Do all this with one hand behind your back and the cap held carefully by its insulated body.  Be careful to observe the correct polarity of the cap or it could explode in your hand.)  Repeat this experiment for anybody to whom you introduce radio repair.

Every day that you work on tube-type radios could be your last. There have been documented incidences of knowledgeable, but careless, individuals being KILLED by electrocution while working on tube-type radios.  Those of us who have survived shocks from a 400-V plate supply will not forget it.  A jolt from B+ left me feeling so weak that I thought I would have to lie down.

Lethal voltages can appear in unexpected places in old radios. For example, AC-type radios often put the high-voltage plate supply, B+, through the field coil of an electro-dynamic speaker coil, thus serving as a filter choke. The speaker leads, if frayed, present a major shock hazard. Also, a transformer fault or a short anywhere in the radio can cause high voltages to appear in unexpected places.

Unplug the set (not just turn off the set's power switch) before working on it.  Even then, there could be a residual charge on the electrolytic capacitors that could give you a jolt. If you must take measurements with the set energized, always work with only one hand, with the other behind your back. (To take voltage measurements between two points, connect an alligator clip to one point, and use a probe for the other point.) Use an isolation transformer (not a variac or autotransformer) to provide protection against line-to-ground faults through your body. Even that won't protect you against shorting yourself across a high voltage within the set.

I have a variac that allows me to bring up old sets at low voltage, increasing voltage gradually while watching for smoke.  Conceivably, an electrolytic filter capacitor could be shorted, blowing up the transformer of an AC set if it’s just plugged into full voltage. (However, I strongly suspect that most radios have been plugged in by their sellers. Call me cynical, but when an eBay ad says the set hasn't been tested because the line cord is shot, I assume that, in fact, the radio has been tested and that it didn't work or, worse, it smoked.)

Another disadvantage of tubes is that they generate a lot of heat, mainly from the filaments, which does add to the stress on components, particularly the tubes themselves.  A typical tube-type radio consumes 30-100 W, which is less than a cent per hour to operate.

For more extensive safety precautions, please read the book Fixing Up Nice Old Radios, by Ed Romney, pp. 4-5.

You Need a Schematic 

To work on a radio, you need a schematic and the skill to read one.  Many schematics are available online, free, at Nostalgia Air: http://www.nostalgiaair.org/  Otherwise they are available for a fee from Antique Electronic Supply:  http://www.tubesandmore.com/ or from JustRadios: http://www.justradios.com/

Vacuum Tubes

Surprisingly, defective tubes are not the most common problem with old, non-working radios.  When tubes are the problem, it’s likely that one is missing, the tubes are plugged into the wrong sockets, or an incorrect tube is installed.  If the tube filaments light up, then there is a very high probability that the tubes are OK. 

For AC-type receivers (ones with a power transformer), the filaments are in parallel, so burned-out tubes are the ones that don’t light.  The rectifier tube's filament  may operate from a separate winding and at a different voltage than the other tubes.  (Filaments aren’t visible for metal tubes, but if a metal tube doesn’t get warm, then it’s a dud.)

AC/DC-type receivers have the tube filaments wired in series—so if one tube is burned out, none of them will light.  Then you can replace tubes one at a time to identify the bad one.  Another approach is to remove each tube and check across the two filament pins with an ohmmeter.  (Get either the RCA Receiving Tube Manual or the Tube Substitution Handbook for pin assignments for each type of tube.)  Replacement tubes are readily available from Antique Electronic Supply or Radio Daze: http://www.radiodaze.com/ .  Many common tubes sell for just a few dollars.

A half-century after the end of the tube-type radio era, vast quantities of surplus new-old-stock (NOS) tubes remain available.  The U.S. Army #76 above was manufactured in 1943; I purchased it new in 2004 for $11.  The Tung-Sol 6U5/6G5, a relatively scarce tuning-eye tube, sells for about $32.  Most common tubes sell for $5-10. Used tubes that test OK are about half the price of new-old stock.

(Incidentally, the term "AC/DC receiver" is somewhat of a misnomer, even though many of them were labeled for use with either AC or DC at 120 V.  Theoretically, without a power transformer, they could be powered with 120-V DC, although such a voltage is and was commercially unavailable to residential users in the U.S.  But even if such a radio were powered with 120-V DC, there could be some problems:  for technical reasons having to do with √2, the maximum B+ plate-supply voltage would run about 70% of the plate voltage when powered with 120-V AC.)

Now, you ask, what if a tube is just “weak” or “questionable,” as would frequently be indicated by 1950s-era tube testers situated in virtually every drugstore?  Balderdash.  I cringe to think of the number of acceptable tubes that were junked using such criteria.  It’s not unusual to encounter a 60-year-old radio with many of the original tubes installed and still working fine.  The rectifier tube and the audio output tubes take a beating from extra heat, so they are most prone to failure. 

(I recall going to the drugstore with my technically challenged father in the ‘50s with a sack full of TV tubes—trying to fix the TV in time for Milton Berle, etc.  The tube tester even had a rubber-headed mallet to rap the tube under test—to identify intermittent shorts.  God only knows how many tubes were ruined by the hammer.  In any case, there would always be a few tubes that tested with the meter’s needle in that dreaded ? or weak range on the scale.  Interestingly, I seem to recall the ? band being wider than either the green-colored good or red-colored bad bands.  Purchasing a few new tubes, Dad would return home with high expectations, followed by the usual disappointment of, “Damn, it still doesn’t work.”  Even TV and radio repairmen, trying to eke out a living, would seldom return a repaired set without one or two “weak” tubes replaced in addition to repairing whatever was the underlying problem.) 

What if the tubes aren’t burned out, but the tubes still don’t light?  This is rather unlikely—roughly equivalent to asking why a “good” light bulb won’t light.  In an AC/DC radio, if the 120-V power cord is intact, the power switch ON, and the tubes good, then it’s hard to imagine why the tubes wouldn’t light since the tube filaments are connected in series right across the 120-V line.  For an AC radio, it’s possible that the transformer is blown, but that seldom happens; to verify the transformer, check to see if there is 6 or 12 volts across the tube filament pins. 

Tubes Light, But Radio is Dead

Carefully check to see if there is B+ voltage.  This is the DC plate supply voltage, about 150 V for an AC/DC radio or 350 V for an AC radio.  If there is no B+ or it is low, then there is something wrong with the DC power supply/rectifier section.  Possibly the rectifier tube or the electrolytic filter capacitors are bad.

If your set seems dead, touch the middle terminal of the volume control pot (being careful to avoid the 120-V power switch terminals).  If the radio produces a hum, then the problem is ahead of the audio section. 

If there is B+, but the radio hums loudly, then the filter capacitors are likely bad.  Replace them to get the hum stopped and to hopefully begin receiving stations. 

Other Possible Problems

If you can hear a slight hum or static, but can’t receive any stations, suspect the R.F. tuning section.  Check to see if the variable capacitor plates are touching, problems with the antenna, or an open antenna coil. 

Carefully inspect all the wiring.  Surprisingly, disconnected wires, capacitors blown apart, and damage from previous repair attempts are often found. 

Recapping 

Once you have the radio working, it’s time to replace all the old wax/paper and electrolytic capacitors.  Old capacitors are trouble waiting to happen.  Be sure to use caps with a sufficiently high voltage rating, or better yet just use electrolytic caps with a rating of 450 V or higher, and non-electrolytic film caps with a 630-V rating.  Usually, the capacitance of the old cap will be marked on it.  In some pre-war models, the caps aren’t marked, so reference to a schematic is necessary to match values. 

The original filter caps may be multi-section caps in a can or box mounted on the top of the chassis.  Leave the can for ornamental purposes, but wire in replacement caps beneath the chassis.  Individual caps can be used in place of multi-section caps.  You can leave the “common” terminal of the old capacitor can intact and use it, and snip and splice the leads to the other terminals to the positive side of the replacement caps.  Don't leave the old caps energized. 

Old pre-war sets frequently had skimpy electrolytic filter capacitors in the power supply.  Increasing the capacity of the original ones helps reduce humming, but don't go overboard--a larger input filter capacitor will increase the inrush plate current of the rectifier tube, causing more stress on that tube.

Don’t replace the domino-shaped silver-mica capacitors or ceramic disk caps—they should last indefinitely.

Replace each cap one at a time, and play the radio after each cap is replaced to detect any screw ups.  When replacing a cap, snip one lead at the capacitor itself, leaving a pigtail to mark the terminal where the new cap will go—with the old cap itself dangling by its other lead.  This will help prevent errors.  When the new cap is installed, snip the old pigtails and remove the old cap. 

Some pre-war radios have a paper capacitor wrapped with several turns of insulated wire.  This is an R.F. choke to trap low-frequency maritime signals that could interfere with the receiver's internal intermediate frequency; they are no longer necessary, and you can safely remove it.  If you wish to keep the coil, snip the leads from the cap—then install a new cap alongside the old one, leaving the coil hooked up.

If the speaker is mounted on the chassis, temporarily cover it with a piece of cardboard to protect it from damage during recapping. 

Capacitor Values 

Don’t try to order the specific capacitors you need for a particular radio.  Buy an assortment that will meet most of your needs.  Here is a suggested assortment: 

            Electrolytics (450-V or higher):

                        10 μF

                        22 μF

                        33 μF

                        47 μF

            Tubular, film-type (600-V):

                        .0022 μF

                        .0033 μF

                        .0056 μF

                        .01 μF

                        .022 μF

                        .047 μF

                        .1 μF

                        .22 μF

Don’t expect to find these caps at Radio Shack.  The demand now is for capacitors with low-voltage ratings, e.g. 25 V, for use with computers and various solid-state devices. 

For most radio applications, the precise value of capacitors is not critical.  For example, if you are replacing a .004 cap, a .0033 or .0056 should work just fine.  Keep in mind that the tolerance on typical caps is ± 10-20%.  Also, most caps are used for bypass or coupling purposes, which are not critical functions.  Electrolytics used as power supply filters usually can be oversized a little, but if you go overboard, the inrush current may increase enough to blow-out the rectifier tube.  Values of capacitors that are used in tuned resonant circuits are critical, but those are usually domino-shaped mica caps that should not be routinely replaced because they have an indefinite life. 

I recently recapped a radio for which I had no schematic and the capacitors weren’t marked with their values.  I just “guesstimated” each cap’s value based on its physical size, probably hitting within a factor of two.  The recapped radio works fine. 

Capacitors may be paralleled to provide capacitance equal to the sum of the individual capacitances. Theoretically, caps can be wired in series to provide an increased voltage rating, but less capacitance—but this is not a good idea in practice, since tolerances may result in an unexpected division of voltages across series caps. 

For electrolytics, great care should be given to installing with the correct polarity.  AC/DC radios often have a low-voltage electrolytic specified with the positive lead connected to the chassis—don’t agonize over it; if that’s what the schematic shows, then it’s correct.  An electrolytic that is installed backwards will blow apart.

Occasionally, two-section paper, tubular capacitors may be encountered. Axial leads come out each end of the capacitor and there is a common connection near the center. These can be replaced with two separate caps. 

In general, increased performance margin may be achieved by using caps with higher voltage rating than the minimum specified for the circuit. 

Great strides have been made in the manufacture of capacitors since the golden age of tube radios.  Wax-sealed paper has given way to mylar, polyester, and polypropylene.  Vintage radios that are recapped with modern capacitors should have an indefinite life.

More on Hum Troubleshooting

A loud, steady hum is most often caused by bad electrolytic filter capacitors.  Next, suspect a bad rectifier tube.

If a hum persists after replacing the filter caps and trying a different rectifier tube, then it is likely that the 120-V power inside the receiver is somehow getting into the audio section of the circuit, possibly by induction.  The heaters on the output tube or 2nd detector may be shorted to other parts of the tube.  Also, the 120-V heater wiring that daisy chains from one tube to the next may be too close to the audio signal path--for example, perhaps the plate-to-grid coupling capacitor between the 2nd detector and the output tube may be shoved too close to the heater wiring.

I wouldn't expect a hum to originate in the R.F. or I.F. sections of the receiver.  These sections are tuned to frequencies that are above the audible range.  Most  persistent hums are not affected by the receiver's volume control, which is usually located between the last I.F. stage and the audio detector—demonstrating that the hum is not originating in the R.F. or I.F. sections.

Speaker Repairs

You will encounter speakers with torn paper cones, most likely the result of your own carelessness and failure to protect speakers with cardboard during radio repair.  Luckily, torn speaker cones usually don’t sound bad.  For repair, try “Magic” adhesive tape (regular cellophane and masking tape don’t stick).  Alternatively, try a bead of silicon adhesive sealant.  If the speaker is beyond such repairs, you can have it reconed by a pro, e.g., John at http://johnsvintageradio.com/ 

Special Issues With AC/DC Radios

AC/DC-type U.S. radios typically have one side of the 120-V line connected to the chassis through a capacitor and/or resistor.  Depending upon which way the power plug is inserted into the wall receptacle, you will measure 120 V from the chassis to ground.  This is disconcerting and potentially unsafe if the isolation cap were to short out.  Therefore, I always install a polarized plug to keep the chassis connected to the neutral leg.  In addition, the hot leg of the 120-V line cord should be connected to the ON-OFF switch, with the neutral leg connected to the other 120-V terminal inside the radio.  It’s best to install the polarized plug before troubleshooting the radio.

The 120-V plug on the left is polarized.  The wider blade will fit only into the neutral side of the receptacle.

Without a polarized plug, or with house wiring where the neutral and hot leg are reversed in the receptacle, or with old house wiring where polarized receptacles aren't used, you are at the mercy of the capacitor which isolates the line voltage from the chassis. If this cap shorts out, full line voltage can appear on the chassis. Therefore, this capacitor should be replaced with a modern Class Y2 or X1/Y2 safety capacitor. For more information on Class Y2 caps, see: http://www.justradios.com/X1Y2capacitors.html. The original capacitors used for this application were just garden-variety caps that don't meet modern-day safety standards.

Some AC/DC radios, e.g. the Hallicrafters S38, directly bonded one leg of the 120-V line to the metal chassis.  What passed for safety was isolation between the chassis and the metal cabinet.  These sets are killers, and should be modified to add a polarized plug.

An assortment of modern safety capacitors.  The disc caps are rated X1/Y2 and are  suitable for connecting one leg of the 120-V line to the radio chassis or across the 120-V line for noise suppression.  The yellow film caps are rated X2, and are approved only for connecting across the line.

The tube filaments for an AC/DC radio are all connected in a series string across the 120-V line. The ubiquitous "All American Five" circuit employed a 5-tube lineup with the heater voltage ratings all conveniently adding up to 120 V and each tube having the same rated heater current. However, some pre-war AC/DC sets used tube complements with heater voltages that added up to less than 120 V, perhaps only 70 V. Many of these receivers employed a resistance line cord embedded in the power cord to drop the filament supply voltage. These resistance line cords, often called "curtain burners," are unsafe even if they are not completely worn out by now. The resistance was located in the line cord, in the form a nichrom twisted wire with an asbestos covering, to avoid adding to the heat in the radio's cabinet—nearly 50% of the radio's wattage may be consumed in the dropping resistance. Sometimes these sets had a transformer just for the B+ supply, so technically they were AC receivers, but with the heaters in series.  I know of no source for replacement resistance line cords, and they certainly would not be permitted by today's electrical codes and standards.

The safest way to deal with resistance line cords is to avoid radios of this type. Otherwise, a metal-enclosed, well ventilated electrical box can be used to house either a dropping resistor of appropriate resistance and wattage or a suitable step-down transformer to drop the heater voltage to the appropriate level. Then, a 3-conductor power cable is hardwired between the box and the radio to carry the reduced heater voltage, 120 V for the radio's rectifier power supply, and a neutral. Don't mount the dropping resistor inside or on the radio cabinet—there will be too much heat.

Another approach is to replace the resistance line cord with a silicon diode, such as an 1N4007; this will reduce the 120-V line voltage to about 85 V (rms). This is usually still too high a voltage, so a supplemental resistor will be required.  Another approach is to use a non-polarized capacitor to drop the voltage; this takes some trigonometry to size the dropping capacitor.  Typically, a cap of about 5-10 µF is needed.  The advantage of a dropping capacitor is that is generates no heat, so it can be safely stuffed under the chassis.  Suitable 400-V Solen caps are available from Parts Express:  http://www.partsexpress.com/

Some pre-war AC/DC radios have a ballast tube--which looks like a small, metal vacuum tube, but is really a dropping resistor for the heater circuit. These should be safe. However, any AC/DC radio with either a resistance line cord or a ballast tube is essentially a cheap design kludge to avoid a transformer or to avoid matching the tube heater voltage string to 120 V. Such radios will likely incorporate other inexpensive features, as well.

There are many nice AC/DC radios that are very collectible and have good performance. Of course, the large, heavy, wooden-cased radios which many collectors find interesting generally will be AC-type sets. Many of the small, attractive art-deco style table-top radios, both pre- and post-war, are AC/DC sets.

I don't know how or if AC/DC radios were designed for the international market where the standard household voltage is 220 V. Everything in this article applies only to 120-V U.S. radios.

Odd and Ends 

My least favorite chore is replacing a dial cord, particularly the ones with really complicated stringing arrangements.  Usually the radio's schematic also includes a dial cord stringing diagram.  Replacement dial cord is available from Antique Electronic Supply or RadioDaze.  Buy the large diameter 0.400" cord.

It’s unusual to find an old radio with the dial lamps working.  Buy replacement lamps (#44 and #47 are the most common) from Antique Electronic Supply or RadioDaze. 

If the grille cloth is ripped or stained, there are many replacement patterns available from Antique Electronic Supply and RadioDaze.  I don’t worry about matching the original pattern as long as the replacement cloth appears OK on the set. 

You might expect an AC-type radio to be isolated through the main power transformer so the chassis could only become energized if the transformer or other wiring shorts to ground.  However, even transformer-type receivers often have one side of the 120-V line connected to the chassis through a capacitor.  Therefore, there is benefit to installing a polarized plug, which also can be used to assure that the ON-OFF switch is connected to the hot leg, thus keeping voltage off the transformer windings when the set is turned off.  The capacitor from one 120-V leg to chassis ground should be replaced with a Y2- or X1/Y2-rated safety capacitor.

Fuses were customarily omitted from old radios.  You can achieve greater protection against short circuits by installing a fuse.  A simple in-line fuse holder, with pigtails, can be installed inside the chassis.  The fuse should be installed on the hot leg of the 120-V line, ahead of the power switch.  For a radio with five or so tubes, try a 1-A slow-blow fuse; for a larger radio with, say 7-10 tubes, try a 1.5-A slow-blow fuse.  A slow-blow fuse is necessary to withstand the large inrush of current when the set is turned on, caused by charging the filter capacitors and by lower resistance of the tube filaments when they are cold.

Old radios can benefit from an Inrush Current Limiter, which reduces inrush current when the filter caps are being charged and the tube heaters are cold, with lower resistance. Such current surge, which occurs when the set's power is turned on, causes wear and tear on tubes. These devices are thermistors that have maybe 100 ohms resistance at room temperature, but drop to negligible resistance when they heat up.  They are installed inside the chassis in series with the 120-line, downstream of the power switch.  A Thermometrics CL-90, with a maximum full-load current of 2 A, is appropriate for most tube-type radios.  They are available for a few dollars from Mouser:  http://www.mouser.com.

Tuning eyes were often provided in pre-war high-end radios.  Sure, they're a gimmick, but still nice.  The most common tuning eye is a 6U5/6G5 tube, which are getting quite scarce.  When available, NOS 6U5s sell for $30, or more, and they don't last as long as most other tubes in the set.  An alternate tuning eye is a military-surplus 1629, which is much more available and typically sells for about $10.  However, a 1629 uses a 12-V filament rather than the 6-V filament of a 6U5.  Antique Electronic Supply stocks an adapter plug/socket which allows a 1629 to be substituted for a 6U5; an alternate, more economical source is Bill Turner, who sells an adapter with a 1629 tube for $18, postpaid.  The adapter includes a built-in voltage doubler circuit for the heater.

The tuning-eye tube on the right is a high priced, 6-V 6U5/6G5.  The tube on the left is an inexpensive military surplus 1629, which has a 12-V filament; with the socket adapter, the 1629 can be substituted for a 6U5/6G5.

 Another alternative tuning eye is a 6E5, which sells for about $20.  A 6E5 uses the same filament voltage and pin-out as a 6U5/6G5, but is slightly more sensitive—i.e., the circular tuning eye may close more with the same station strength.  But, in many cases, this higher sensitivity may actually provide improved performance over the standard 6U5/6G5, particularly for weak stations.

The typical failure mode for tuning eyes is not for the filament to burn out, but rather for the display to become faint, much like a dying TV picture tube losing the potency of its phosphors.  A tuning eye exposed to direct sunlight will be ruined, so such radios should not be positioned near windows with direct sunlight exposure.

Repairing radios takes good eyesight and good lighting.  My bifocals, while fine for reading the newspaper, aren’t strong enough for the fine work involved in soldering connections, tracing wiring, etc.  I bought a stronger pair of reading glasses at the drugstore that help greatly.  An overhead fluorescent fixture is nice, but it should have a convenient switch to turn off the light when it causes excessive radio static. 

Speaking of soldering, you may own a small 25-W pencil-type soldering iron used for working on printed circuit boards and solid-state devices.  Forget it.  For tube radios with point-to-point wiring, you need a real soldering gun.  Mine is a classic Weller model 8200-N, dual heat (100/140 W), with a spot lamp.  Radio Shack sells replacement tips. 

A good electronics workbench is a 2’x6’ sheet of 5/8” plywood, supported by two sawhorses that bring the surface up to about waist high.  In all cases, a non-conductive workbench, e.g. wood not steel, should be used for safety.  Safety can be further improved by wearing rubber- or crepe-soled shoes and standing upon a rubber mat, particularly if working on a concrete floor.  These measures help protect against ground faults across the 120-V AC, but you are still at risk of shorting yourself across AC or DC voltages within the set itself.

Electronics work involves many interruptions for fetching parts, tools, etc.—so it's best to work standing up, not sitting down.

My radio-repair workbench--too messy!

Some items sold for scale model builders are a good substitute for hard-to-find original radio parts.  For example, thin plastic sheets used for model airplane cockpits can be fashioned into replacement, transparent dial covers.  Tower Hobbies is one source:  http://www.towerhobbies.com/   If your broken dial lens is round, plastic and glass replacements are available from Bill Turner:  http://www.dialcover.com/

Cosmetics and Authenticity 

My main enjoyment is repairing and preserving radios—to use them as working, everyday receivers; to preserve their historical value for the future; and to use as gifts to people who appreciate them.  I’m not keen on refinishing cabinets; I’m not a carpenter or cabinetmaker.  Therefore, I prefer to buy radios with reasonably presentable cabinets, whether wood or plastic.  Of course, wood radios have a special appeal.  Old radios with glossy, refinished cabinets do not seem right to me.

If a wooden cabinet is in halfway reasonable condition, I will just give it a treatment with Kramer’s Antique Improver:  http://www.kramerize.com  Some cabinets have a black discoloration that I remove with Kramer’s Blemish Clarifier and steel wool.

If a wood cabinet must be refinished, here's the drill:  with furniture stripper, remove the old finish; sand; re-stain as desired; and spray with several coats of semi-gloss lacquer.  My neighborhood Ace hardware store stocks Deft lacquer in an aerosol can.

Some purists think it is very important to preserve and restore the authenticity of old, collectable radios.  For example, instead of replacing old paper/wax capacitors with modern “orange drops” or the like, they painstakingly conceal modern caps within the shell of an original paper cap.  I admire these people, but I don’t want to be one of them.  In fact, I prefer not to buy a fully restored radio—what’s the fun in that? 

I won’t clean a chassis down to shiny, new condition.  To do this, I think you would almost have to remove all the wiring and sockets, and clean the chassis in an acid bath and possibly re-plate.  (Another approach for cleaning a rusty chassis is with electrolysis:  running a DC current from a battery charger through a aqueous solution of washing soda, with the rusty chassis on the negative polarity and a piece of iron on the positive terminal.)  I do give the receiver a light cleaning—blow out underneath the chassis with canned air and give the top of the chassis, including the tuning capacitors, a lick and a promise with Radio Shack electronic cleaner.  I’ll Windex the dial lens and each of the tubes.  Also, volume controls and other potentiometers should be given a squirt of tuner cleaner, available at Radio Shack, to keep them turning freely and to prevent static and noise. 

Pushbutton tuning became a popular gimmick with nice old radios.  I don’t worry about setting up the pushbuttons for particular stations and, in fact, I’m not overly bothered if the pushbuttons don’t all work.  However, one or more missing pushbuttons ruins the look of a radio—calling to mind a goon with missing teeth. 

Most pushbutton escutcheons have little rectangular indentions in which to paste paper tabs with the printed call letters for the station associated with each button.  If an old radio has call-letter tabs for the pushbuttons, I leave them there for nostalgia purposes and to provide some indication of the geographical area in which the set was originally used.  If there are no call letters, then I like to stick on new ones for stations that were once meaningful to me, e.g., KDKA, WDAF, WILL, KSAC, and WCFL.  Sheets of U.S. call letter tab assortments are available from Antique Electronic Supply.  Also included are tabs for ON-OFF and MANUAL, since a pushbutton may have been assigned as the power switch or used to enable the manual tuning knob. 

Some radios are missing the decals used to identify tuning knobs, tone control, the brand name, etc.  Replacement decals are available from Rock-Sea Enterprises:  http://members.aol.com/RockSeaEnt/

Replacements for missing decals.

Alignment, Troubleshooting, and Test Equipment 

Most troubleshooting can be done with a garden-variety volt-ohm meter.  For unusually difficult situations, an oscilloscope, signal generator, signal tracer, and frequency counter are helpful.  For radio work, state-of-the-art equipment is not necessary or even desirable.  Vintage Eico equipment, frequently available on eBay, is ideal.  Modern test equipment is usually designed for high-frequency work, not the audio frequencies and low R.F. encountered in vintage radios.  New signal generators often can’t even go down to 455 kHz, the customary intermediate frequency of superhet radios.  Also, it is desirable to be able to impress an audio signal on the R.F.—a feature available on vintage signal generators.

A modern digital volt-ohm meter may not be desirable.  A digital display provides rapidly changing gibberish for a voltage or resistance that is varying.  An analog VOM, such as a Simpson 160, is preferable.  Even better, get a vintage Heathkit vacuum tube voltmeter.  I built one in the ‘50s—it went astray, so I’ve since purchased a used one.  A Heath VTVM can be modified to accept banana plugs or BNC leads instead of the silly phono plug originally used.  (For a suggested modification to vintage Heathkit VTVMs, see Randy Kadding's article at:  http://theheathkitshop.com/vtvmprobefix.html .)  Test leads and plugs are readily available from Mouser Electronics.  Many manuals for vintage test equipment are available online at K4XL's BAMA website:  http://bama.sbc.edu/

Now, let’s address receiver alignment.  Superhet AM receivers have several tuned circuits that can be adjusted to optimize performance.  Detailed alignment procedures are often included with the set’s schematic.  In general, it’s best not to fuss with alignment if the receiver is working reasonably well.  In most cases, I have found that the original factory alignment, after all these years, is still "dead on."  But for those who insist, here is a one approach: 

1. With a signal generator at the intermediate frequency (typically 455 kHz, but not always) injected into the I.F. section of the gang tuning capacitor, align the I.F. transformer trimmers for maximum output.  (Note:  if you use an old analog Eico signal generator, you need to check its calibration with a digital frequency counter or digitally tuned scanner.)

2. With the tuner capacitor set at maximum capacity, inject a signal toward the upper end of the broadcast band.  Adjust the antenna trimmer cap (located on the tuning capacitor) so that output is maximum.

3. With the radio tuned to a station of known frequency, adjust the oscillator trimmer so that the dial points to that frequency.

Actually, there is a much simpler alignment method that works most of the time.  Tune to a steady, medium-strong broadcast station.  Adjust each of the two trimmers on the 2^nd I.F. transformer for maximum volume.  Then do the same for the 1^st I.F. transformer.  Now, reinstall the chassis in the case and put on the knobs; you’re done.  The I.F. may not be exactly 455 kHz, but as long as everything is tuned to whatever the I.F. frequency is, it will be good enough.  Also, some weird stations at the far end of the dial may be off scale, but so what?  Have you listened to any of those stations recently?  If one or more of the I.F. transformer trimmers reaches the end of its range of travel before achieving maximum volume, then the I.F. has probably drifted too far from 455 kHz, and a full-blown alignment is in order. 

Ideal Radios to Buy 

My criteria for selecting a radio are based on its interest and attractiveness to me, its historical value, and its usefulness as a real, working radio.  I can usually tell by looking whether I like it. 

Most pre-war sets are interesting, but I tend to confine myself to the superhetrodyne era of the '30s and '40s.  The earlier R.F.-tuned Atwater Kents, etc., are not exactly what I would put in our guest bedroom to be used by my technically challenged visitors, and their prices are out of sight anyway.  Instead of having a fixed intermediate frequency, each R.F. stage must be separately tuned to the station frequency—about as practical as a crystal radio—or equipped with a ganged variable capacitor with a separate section for each stage. 

Replacement vacuum tubes, new-old stock (NOS), for most pre- and post-war models are still available at reasonable cost (less than $5 each).  Some older tubes may be a little more pricey, but there are often cheaper substitute tubes that will work fine.

A pre-war set’s condition may be a little worse for wear, including wiring insulation that has become brittle and is flaking off—no hill for a stepper, though.  Pre-war models may include police and international bands.  (When I say “police,” I mean the obsolete band just above the AM broadcast band used by the old-time coppers.)  FM, when included on pre-war sets, will cover an obsolete band that is useless today.

Post-war models, say 1945-47, are very similar to their immediate pre-war counterparts, but often in better shape.  It seems that some pre-war wooden cabinets were stockpiled while defense contracts took priority, only to be stuffed with electronics after the war’s end.  The quality of pre-war models is usually high, with inspection stamps here and there.  Immediate post-war models are also of high quality, as if the army/navy specs were still applicable and the government inspectors were still in the plant. 

A big change, for the worse, began in the early ‘50s.  All of a sudden, cost was king, culminating in the ultimate abomination:  printed circuit boards with miniature tubes.  The late ‘40s and early ‘50s do have the redeeming virtue of the advent of modern FM. 

Finally, with the introduction of transistors and cheap Asian radios, my interest in radio receiver technology stops.  It is said that the function of any single vacuum tube can be replicated with five or more transistors; what an indictment of transistors!  Transistor receivers or any set with printed circuit boards are hell to work on—and their cases look cheap.  Most of them sound cheap, too.  These receivers may one day become rare, if only because so many of them have been put in the garbage.

In all fairness, crass commercialism is not completely to blame for the decline of quality radio receivers; with the widespread advent of television in the early '50s, consumers were no longer interested in high-quality radios for their living rooms.  And, ironically, the banishment of nice, old radios to the attic may have assured an almost inexhaustible supply for future collectors and tinkerers.

The large floor-model consoles are interesting to me, but I just don’t have the room for more than one or two.  I concentrate on U.S. table-top models.

I’m not attracted to battery-powered "farm" radios—but with battery eliminators, they may be useful.  Note that when an old radio is called a "portable" model, it means that there is a carrying handle on top of the case.  A battery-powered model is called, duhh, a battery-powered model.  Battery-powered models required two or three batteries:  a high-voltage B battery for the plate supply, an A battery for the tube heaters, and sometimes a small C battery for grid biasing. Alternatively, a single low-voltage battery could be used, such as a 6-V lead-acid battery, and the B voltage generated by a vibrator circuit built into the radio; this was common for farm radios using a wind charger.

© Doug Criner, 2004-06