Sonny's tech tips for vintage radio, TV, electronic service or restoration

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The information Listed below is intended for folks with understanding, and or experience in electronic servicing. The information  listed are tips and suggestions for the novice as well as the experienced. 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.

If you don't understand the potential hazards getting into electronic and electrical equipment with potentially lethal voltages (house current included), perhaps you should not be doing so.

If you want to share and any of your successful restoration secrets or practices, send 'em to me. If I find them to be helpful, I will post them and give you credit.

• First; NEVER DO THIS!

• Basic safety and repair tips

• Cabinet repair Wood, touch up, spiffing

• Cabinet and other cosmetic restoration/repairs

• Cleaning, basic

• Capacitors, transformers and canned components

• Misc service tips, radio, phono, speakers, amplifiers

• Noise, controls, switches or when tuning in a station

• Operating vintage equipment

• Pot Metal Issues

• Tube Testing

• Voltage & Resistance Measurements

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FIRST, Some advise on restoring old electronic gear:

Tubes are just the beginning of restoring any old piece of electronic equipment. There are many other parts in that old instrument that don’t hold up anyway near as good as vacuum tubes. Capacitors made back before the 1970s were the number one failure in electronic equipment and will for sure be so in any old TV, Radio and any other piece of electronic gear thats been sitting around for years.

REASON; Capacitors are kinda' like very small batteries and have a limited life, the older the manufacture, the worse, the quality and life. Vacuum tubes are sealed in glass, they fail, not because of age, they fail due to use, loss of vacuum, gas, internal shorts or *overheating. Tubes can be found (even used ones) that are still quite good. Can’t say that about capacitors.

 

So before you invest in a bunch of tubes thinking they may bring your old radio or television back to life, be informed of the above.

 

*Overheating is usually caused by a faulty capacitor!

REPAIR TIPS and SAFETY

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.

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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!

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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.

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Tip #3A  - Dealing with resistance line cords. I have a separate page for this issue, click HERE.

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Tip #4 DON'T .......PLUG THAT OLD RADIO IN!! Click here for this tip.

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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.

WORKING WITH WOOD CABINETS

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.

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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. 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.

More Info <

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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. "Mar-A-Way" works well on Faux finishes also but don't use steel wool or any other abrasive.

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Tip #19  Deluxing or "Spiffing Up" a wood radio cabinet. (See tip 19A for complete refinishing)

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".

(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.

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Tip #19B     Basic cleaning: dials, plastic, metal,  painted and  printed surfaced objects

One must be carfuls when performing the simple task of cleaning. What worked the last time may not work on the next object that you might have worked successfully for the same as one you did before. IE, some dial scales especially some of the ones used on Zenith radios are (even the black painted metal ones) water soluble.

With this in mind, I suggest; before doing the cleaning, using Q-tip cleaner wetted with the intended cleaning agent make a small test on an inconspicuous area with trh cleaning agent before proceeding.

Most objects dirty with household grease, grim and dirt can be cleaned with soap and water, maybe a bit of ammoniated cleaner for more stubborn grim.

The above may work for most, if not try some mineral sprits (ordinary paint thinner). Do not use the crappy so called “green” stuff (which is really milk white in color) as is most of newer paint products promoted by the tree hugging crowd does not work as good. Also NEVER use Lacquer thinner or Alcohol as those products will very likely remove the text and paint. Lighter fluid is also a good all ‘round cleaner that will not attach paint or plastic finishes.

If the dial is rusty or corroded there’s not much that can be done. Anything stronger will also remove the text and paint as well. That’s why I made replica’s of the dial scales

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CAPACITORS, CONDENSERS & CANNED COMPONENTS

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.

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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.

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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 #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 those of  few other brands. Not one of the many I've encountered 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 or damage) leave ‘em alone. They are not electrolytic's, 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.

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Tip #28 Re-stuffing electrolytic capacitors

 When simply installing modern ones is not an option, here's   what I do.

1)        Cut the original can in two, cut about ½” above the mounting base.

2)        Gut out all the old material (a time consuming nasty job on some of ‘em). Clean and smooth in and around the sawed area including the inside of the can.

3)        Stuff the top section of the can with new modern caps, a few properly placed dabs of silicon adhesive will keep the new caps in place, no need to fill the can with anything.

4)        Drill tiny holes in the base (for the new capacitor’s lead wires to feed through and make the wires an inch or so longer than needed.

5)        Now cut a paper or plastic tube (about an inch or so long) that will snuggly fit inside the original can.

6)        Line up and mark the positions where the two can halves join together (as your cut will not likely be symmetrical).

7)        Using JB Weld, the black stuff (and not the quick set) or use any brand of the Epoxy Steel (grey stuff). Place a small amount on the edge of one end of the interior paper or plastic tube and a small amount on the interior of the newly stuffed capacitor can with lead wire/s sticking out and slide the interior tube inside the main original can giving a twist or two and leaving just enough of the interior tube protruding so as the snuggly fit the base section onto.

8)        Thread the wires though the proper holes of the base half of the can and ring the base area with more epoxy. Press the two halves together making sure the two halves line up together with a tight fit.

9)        Remove as much of the excess epoxy as you can without disturbing the positioning of the two can halves.

10)    While the epoxy is still workably, hold the two can halves together and keep in place using a rubber band, tape, clamps or any method you can think of to keep the can halves tight together until the epoxy cures.

11)    When fully cured (about 48 hours) the excess epoxy can be tooled or sanded away to make a smooth surface. Once you have a smooth surface at the area that was sawed and epoxied, you can wrap it with a ring of the aluminum metal ductwork tape or other aluminum adhesive back material that you like.

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DEALING WITH NOISE

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.

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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 body wash. 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. When this product was first introduced back in the mid 1970s, the factory rep. visited the shop I owned. I still recall one of his key comments about using the product; "a whiff of the stuff works better than a soaking".

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".

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MISC SERVICE TIPS

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.

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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.

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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 #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

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