[cathoderay57]

I use the Avo analogue meter on the MegOhms range and if the DC resistance doesn't go to infinity then the cap is useless. You can get away with a cap that shows a DC resistance of, say, > 1 MOhm in some circuits such as cathode decoupling capacitors where the cap is in parallel with a resistor of a few hundred Ohms. I once read an article about reforming leaky paper caps but IMHO that would be a complete waste of time. If the cap shows virtually infinite DC resistance on the low-voltage Avo test, it still is not necessarily OK at full working voltage so in critical applications such as grid couplers it is worth applying HT to one end and a voltmeter across the open end and HT negative. There should be an initial pulse then the voltage should drop to very close to zero. As said above, in these applications, unless you are a stickler for using original components, it's just simpler to replace it with a new one. In less critical applications I usually rely solely on the low-voltage Avo leakage test and check the valve electrode voltages against those quoted in the Service data when I power up the set. As said many times before on this Forum, the service sheet voltages were often measured using a low impedance voltmeter and so, using a DVM, you should often expect higher voltages than those quoted, especially in high impedance circuits. Jerry