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Did you know why most Antique Radios fail to work?

Most antique radios failures are due to dried out CAPACITORS. Most capacitors are made with foil and a dielectric. As time goes by the material used as a dielectric can dissipate from the body of a capacitor, causing it to fail. Sometimes they short causing other failures, but most of them just OPEN-UP. The electronic circuit acts as though the capacitor isn't even in the circuit. Just replacing a couple capacitors can repair most antique radios. Most of those are due to FILTER CAPACITORS failing. How many radios have you powered up only to hear a loud annoying hum? A filter capacitor is a major component used to turn AC current into DC current. I don't know of any radio that actually uses AC current in the electronics! This will explain where the hum comes from, and why. For a couple bucks you can repair this problem yourself!

Example 1.1 shows you a very basic working DC power supply output. Notice the (B+), clean and flat! As it should be!

This example, 1.2, shows what the output looks like when the capacitor is not there OR when it's OPEN.

This condition is called a ripple. The ripple causes the loud hum, because the noise is amplified through the circuit of the radio. Because of its overwhelming characteristics the volume control may not work either!

WHAT ABOUT CAPACITOR VALUES

Actually the exact replacement value only has to be close. In most circuits the value can be doubled, even tripled. Too much filtering doesn't hurt in this case. For example, a 12mf (microfarad) capacitor can be replaced by a 10mf or 20mf. I would go with a higher value before a lower one though. Typically your best bet would be to stay within + or - 20% of the original value.

WHAT ABOUT VOLTAGE RATINGS

Never replace a capacitor with one rated below the original capacitors voltage! HOWEVER, a replacement rated above the original value is acceptable. That's about it. If the original value is 350 volts, then any voltage rating higher is acceptable. The voltage rating on a capacitor is a maximum value. A 400-volt, 450-volt, or even 600-volt can be used to replace a 350 volt capacitor.

WHAT ABOUT DUAL OR MUTIPLE CAPACITORS

Dual or multiple capacitors are capacitors with more than one capacitor inside a single package. BUT, They don't have to be inside a single package. They are used to simplify the manufacturing of the radios. In fact it would be a better bet to replace these capacitors with single capacitors. Multiple capacitors cost more and are harder to find. You will also find that sometimes only one of the capacitors in the package is bad. If you did have single capacitors, you could replace just one at a lower cost. In any case take a look at example 2.1

Take a close look at the value and voltage ratings on the replacement capacitors. This is a prime example concerning values and voltages. If there were a forth wire, then you would add a third capacitor. See example 2.2 below. Save yourself the heartache and expense trying to find a replacement.

LETS USE UP THE CAPS YOU ALREADY HAVE

Here are a few other things you can do with capacitors. This is great if you have capacitors already and don't need to spend the extra money on more! In example 3.1 you will see how we can make a 50mf cap from two 25mf caps.

Notice the voltage values are different. In this case the total voltage can NOT be higher then the lowest voltage value. This is now a 50mf, 160-volt capacitor. Now take a look what happens when we add another capacitor. Example 3.2 is now a 100mf 160-volt capacitor. I guess you got the point by now. This is called a parallel design. Just remember capacitors add up in this configuration.

Now lets make a 12mf out of two 25mf capacitors. What we want now is a configuration that divides capacitor values. Simply put Series configuration. Example 3.3 will show the differences.

Now lets review. Always watch your voltage ratings! Always watch your polarity (notice the + on all my examples) these are called electrolytic capacitors because they have a polarity. Be sure you discharge your capacitors before you handel them. For any questions e-mail me, to order caps CLICK HERE I have limited values to start! I will continue to add stock, and I will continue to ADD technical notes.

So for both our sakes check back soon!

04/08/02 rev3

Radio Repairs  PART II

Did you know why most Antique Radios fail to work?

Most antique radios failures are due to dried out CAPACITORS. Most capacitors are made with foil and a dielectric. As time goes by the material used as a dielectric can dissipate from the body of a capacitor, causing it to fail. Sometimes they short causing other failures, but most of them just OPEN-UP. The electronic circuit acts as though the capacitor isn't even in the circuit. Just replacing a couple capacitors can repair most antique radios. You may hear nothing, or you may experience a loss of selectivity and/or sensitivity. This will help to explain why for a couple bucks you can repair these problems yourself with a few capacitors!

Example 1.1 shows you a very basic working bypass filter. Used here to ensure AC does not get through, but DC does.

This example, 1.2, shows just the opposite. This will allow AC through, but not DC.

Example 1.2 could be used as an input signal conditioner on an amplifier. Blocking DC, which can damage your speakers as well as your amp. However it will allow AC or audio (AC in many frequencies) pass. If it were to open then nothing would get through. Or the output may sound weak and distorted. On a very basic scale AC sees a capacitor as a short circuit. DC sees a capacitor as an open. SOOOO, why use capacitors in a DC circuit? One reason we already know. To block AC and or noise. If we read the previous Tech Notes, we also know they are used to filter DC. With a couple more components we use capacitors for oscillators, band pass filters, and so on. We won't go that far. Beside I'm not sure if I can! I want to keep this simple to insure it could aid anyone.

WHAT ABOUT CAPACITOR VALUES

Actually the exact replacement value only has to be close. For example, a 0.56mf (microfarad) capacitor can be replaced by a 0.47mf, 0.50mf or 0.68mf. Typically your best bet would be to stay within + or - 20% of the original value. Remember the original parts were not very accurate. That's why old electronics has so many adjustments. You could not replace a 0.1 with a 0.01 though. Notice the decimal points. However a 0.15mf can be replaced by a 0.1mf in most cases. If you find a circuit that calls for a certain value with a 5% or better tolerance, then you should get an exact replacement if possible.

WHAT ABOUT VOLTAGE RATINGS

Never replace a capacitor with one rated below the original capacitors voltage! HOWEVER, a replacement rated above the original value is acceptable. That's about it. If the original value is 630 volts, then any voltage rating higher is acceptable. The voltage rating on a capacitor is a maximum value. A 630-volt, 1000-volt, or even 1200-volt can be used to replace a 600 volt capacitor.

LETS USE UP THE CAPS YOU ALREADY HAVE

Here are a few other things you can do with capacitors. This is great if you have capacitors already and don't need to spend the extra money on more! In example 3.1 you will see how we can make a 0.1mf cap from two 0.047mf caps. It's simple they add up in this configuration, called parallel. Notice there are no polarities. These are non-polarized capacitors. So the direction does not matter.

In this case the total voltage cannot be higher then the lowest voltage value. This is now a 0.1mf, 400-volt capacitor. Now take a look what happens when we add another capacitor. Example 3.2 is now a 0.2mf 200-volt capacitor. I guess you got the point by now. Again the total voltage cannot exceed the lowest voltage value capacitor.

Now lets make a 0.047mf out of two 0.1mf capacitors. What we want now is a configuration that divides capacitor values. Simply put, Series configuration. Example 3.3 will show the differences.

Now lets review. Always watch your voltage ratings! Use the lowest voltage value when connecting in series OR parallel. Always discharge capacitors before handling them. Capacitors can hold a charge for a long period of time. For any questions see my web page www.wjoe.com, to order caps www.wjoe.com/capacitors.htm I have limited values to start! I will continue to add stock so, please check back. I figure these notes would be my way of giving back for your patronage. Please be sure to read the disclaimer.

This web site and services are free. I feel I can give something back for your patronage. THANKS!

Be sure to check back for more Technical Notes, as more will be added!

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09/30/07