Should a capacitor be replaced if a voltage is low?

Well, if the absolute voltage measured across Rg is in the order of one tenth of the nominal bias voltage or more, the capacitor must be replaced regardless of its leakage. On the contrary, if the measured voltage is low, say few millivolts, no need to replace the capacitor. This can be the case of a low ohmic value for Rg, say 10 to 47 kohms.

Can a capacitor run at a low voltage?

They operate at very low voltage: -2 volts fixed bias minus the AVC. In this condition, according to the Ohm’s law, no appreciable current can be flow through even a 2 megaohms insulation resistance. Moreover the resistance across the capacitor at such low voltage is much higher than the one measured at high voltage.

Can decoupling capacitors cause excessive voltage drop?

Of course, this is not always true. In other cases, limiting resistors on screen grids may have values of 220 Kohms or higher and a capacitor with leaks in the same order of magnitude as above may cause excessive voltage drop. Now let us examine the decoupling capacitors C4 and C5 in the grid biasing circuits of the same tubes.

Where can I buy a vintage radio capacitor?

Companies that cater to vintage radio collectors include Antique Electronic Supply and Just Radios. General suppliers such as Mouser and Allied carry capacitors along with thousands of other parts. If you don't have a schematic, you can often read the value of a capacitor from its case. Different types have different markings.

What type of capacitor is used in a radio circuit?

Paper caps are the most abundantly used type, found in all areas of the radio circuit for general coupling, decoupling, and filtering. They are non-polarity sensitive, with values typically ranging from .001uF to .47uF. Most of these capacitors are clearly labeled with both value and voltage rating, with the actual measured value being quite close.

What are the most common defects in Old capacitors?

The most common defect in old capacitors is leakiness. An ohmmeter can't test for leaking because the voltage that it applies is too weak. A capacitor might look OK when testing with an ohmmeter, yet leak like crazy when enough voltage is applied.