A condenser with any leakage is unacceptable. This means that if the needle springs upward to any degree at all, it must fall back to EXACTLY where it started. You are using a resistance check meter, of course (multi-meter). Use the X10,000 scale whenever you test condensers. Condensers smaller than .001 MFD will normally not deflect the meter at all during their charge-up period. They charge up too quickly for the sluggish meter to respond. However, any meter with leakage will cause the meter to jump up, and it won't fall all the way back down. When I say unacceptable leakage, I mean that with the needle zeroed out, it should fall back to exactly where it started. It can't linger above this by even the thickness of the smallest hair. If you remove the condenser from the meter and the needle moves at all downward, then the condenser has unacceptable leakage.

Whenever you test condensers, be sure to remove them from the circuit that they are in. Resistors and other devices wired into the circuit will make you think that condensers are leaky when they really aren't. Also, your hands allow enough current to flow to severely throw off meter readings. Do not touch both condenser or meter leads at the same time with your fingers or you'll think that every condenser is leaky.

It is easier for you to see why any leakage at all is detrimental to a radio when you take into consideration that tubes are EXTREMELY sensitive devices. They are far more sensitive than transistors, though transistors can have trouble with leaky condensers, too. The grid of a radio tube is so sensitive that it can measure incredibly small voltages. I can't think of the exact number, but it is amazingly small. Think radio waves in the sky, and you're probably at least 100 times over the actual figure. Also, very large value resistors are used in supplying bias voltages to the grids and such. By large value I mean high resistance, like in the millions of ohms. If a condenser is leaky in the millions of ohms, it is easy to see how its leaking voltage from one circuit to another will severely affect performance of the successive or even preceeding circuit. Usually the successive circuit is where the grid is concerned, and this is where you have the most trouble in radios (since it is so sensitive).

Good condensers do not pass current ever, but hold charges and allow circuits to influence eachother. This is why a condenser only "passes" alternating current. Once a condenser charges up, it cannot influence a circuit anymore, so if you supply it with direct current, it'll charge up and then stop. They are used to pass and bypass alternating currents like radio signals and audio signals, and are used to block the direct currents that are used in each stage of a radio.

I do not mean to get too detailed. I can go into more detail, but I assume that you already know something about radio. If you want more detail, I'll give it. I just want you to understand the importance of perfect condenser operation. This is probably the biggest reason for radio failure (along with dirty switches and drifted resistors). It cannot be overstressed. Once you're done replacing bad condensers, you'll probably find that many of the weak tubes which you replaced actually work quite well. A radio must perform perfectly once you are done working on it. Too many people have this idea that old radios are inferior and have inferior sound quality. There were inferior circuits back then just as there are now (some modern radios sound like junk). For the most part, however, the only thing lending to bad sound quality with a properly working old radio is the speaker, and in some cases bad circuit design. Poor quality sound has nothing to do with tube technology. With most AM radios of the 1930s and early 1940s, speakers, not necessarily capable of full range, but of rich tonal quality, were used, so most of these radios should be able to put the poor quality assumption to shame, especially since most modern AM radios cannot in any way compare to the tonal quality of these old radios. Modern ones sound grainy and raspy. The old radios make up for the missing highs and high fidelity with a mid and low range that is very pleasing. With your stereo, I'll assume that high quality speakers were used. If they were balanced properly for natural tone reproduction, you should be able to place the needle upon a Toscanini record and be held in breathless suspension (assuming that the record has been cared for). Danse Macabre is a perfect example of his fine work.

Thomas