Capacitor Installation Tips
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When restoring an antique radio it standard practice to replace certain of the radios capacitors. This is known as "recapping" a radio. An old radio may work with it's original caps...but for how long ??....and how safely ?? If the radio is going to be sold with a guarantee or is being given to someone as a gift, you should "recap" the radio.
You will want to replace all the paper and electrolytic capacitors. However, "do not replace the mica capacitors". Mica capacitors very rarely go bad and if you replace them it will throw off the radios tuning. Replacing the mica capacitors will do more harm than good. Only replace a mica if you are sure it is bad (which is rare).
Like mica capacitors, ceramic capacitors also very rarely go bad. Do not replace ceramic disc capacitors unless you are sure one has gone bad.
Some radios use what are known as "line-filter" capacitors. These capacitors connect across your radios power line and/or go from your power line to ground. When replacing these capacitors, you should use special AC Rated Safety Capacitors. These special capacitors with improve the safety, performance and reliability of your radio. If you would like to learn more about these "safety capacitors", there is a link to the ABC's of Safety Capacitors near the bottom of this page.
Get a schematic (and parts list) before you start your recap job. It is often impossible to read the values that are on the original capacitors. Also, if the radio was repaired at some time in the past, there is a good chance someone threw in the wrong size capacitors, just to get the radio working. Without a schematic you'll be guessing.
Before replacing the capacitors, check the radios' resistors. Since you will be replacing the capacitors, you should snip one lead of each paper and electrolytic capacitor. This will help prevent false resistance readings.
Put heat shrink (spaghetti) tubing on the leads of the capacitors and resistors before you solder them into the circuit. This will help prevent dangerous shorts. If you need some heat shrink tubing, just "let us know" and we will be glad to add some to your capacitor order at no charge.
Always check a capacitor before installing it. Although it is very rare, every once in a blue moon, a new capacitor will be defective or off spec. Taking ten seconds to check a capacitor can save you hours of troubleshooting…..only to find out you accidentally installed a brand new "bad" capacitor.
If you need a higher uF than is available from your retailer, you can connect a couple of capacitors in parallel (side-by-side). For example if you need 200 uF at 450 volts you could connect two 100 uF / 450 volt capacitors in parallel and you would end up with 200 uF at 450 volts. You have kept the voltage the same while doubling the uF.
In "theory" connecting capacitors in series (end-to-end) should result in a higher working voltage. For example "in theory" two 100 uF at 450 volts in series should give you 50 uF at 900 volts (double the voltage and half the uF).....however, connecting capacitors in series is not recommended because with a series connection, one capacitor will usually end up getting more voltage than the other. This is because the leakage resistances of the two capacitors are rarely the same and the capacitor with the higher resistance will get a greater share of the voltage (which will often result in a series connected capacitor breaking down).
Please remember to always work safely. The high voltages stored in large capacitors can kill! If a radio has been turned on in recent weeks some of the capacitors (especially the electrolytic capacitors) may be holding deadly voltage charge. Before working with these capacitors they should be completely discharged. This can be come by (bridging) connecting the two ends the capacitor in question with a high wattage 1000 ohm resistor via insulated clips and leads.
