Replacing capacitors in power amplifier

Do electrolytic capacitors need to be replaced?

Generally its only electrolytic capacitors that need replacing, the most critical being the ones serving as filters in the power supply. Occasionally resistors that are stressed (like ones near the power tubes) can fail, and in some designs its a good idea to replace some of these with higher tolerance ones before they fail.

When should a capacitor be replaced?

But the capacitor must be replaced only when this drop becomes excessive. A simple way to evaluate the proper insulation of the capacitor is to remove the tube from its socket and measure the voltage drop across Rscreen, or VB+ minus Vload. If this drop is in the order of a couple of volts or less, no need to replace the capacitor.

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 I increase the capacitance of a capacitor?

There is no problem increasing the capacitance (just stick to the power rating or use a higher rating), though you probably won't notice any benefits, and will prove more expensive. Remember the larger the capacitance, the longer the cap will take to charge/discharge. Also, I wouldn't worry too much on getting exotic capacitors.

Should you replace a capacitor with a small leak?

Then, in the examined high-voltage circuits there is no normal reason for replacing capacitors showing some small leakage. 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.

How do you know if a capacitor should be replaced?

For electrolytic caps (and really all caps), there are testers that check "equivalent series resistance" (ESR), and leakage (or dielectric strength). Then it becomes a pretty clear result of pass/fail instead of "replace on general principle". ... Other than capacitors what parts within an amp need replacing because of age?