Neal,
May want to check the coupling capacitor connected to pin 5 of the 50C5. If it is leaky it will reduce the negative bias on the tube and cause it to run hot. If the set uses a 12AV6 then the cap would be between pin 7 of the 12AV6 and pin 5 of the 50C5. There should be no leakage in the cap.
Radiodoc
When testing your condensers, any condenser which has any leakage what-so-ever, is an unacceptable condenser. Checked on your X10,000 scale, condensers under .001 MFD may not deflect the meter up at all for their normal charge-up, but all condensers will deflect the meter up when leaky, and it'll stay up. The meter, if it deflects up at all, must fall back to EXACTLY where it started. Anything less is unacceptable.
Thomas
Neal,
If the capacitor tests ok then it shouldn't cause the 50C5 to run hot. However, the 50C5 will get pretty hot after all it is a 50 volt tube. If the plate load of the 12AV6 is around 470K ohms and the grid resistor of the 50C5 is around 470K then you probably could get by with a cap around .001Mf to .005Mf. Thomas had some good points in his post so you may want to reread. All of the caps around both tubes can not have leakage. May want to check the 50C5 cathode resistor for correct value. Check for a capacitor across the output transformer and check it for leakage. And of course don't rule out you may have a bad 12AV6 or 50C5 tube.
Radiodoc
By the time this radio was produced, such condensers were not uncommon. They were like the baby of the microchip (everyone thinks that microchips have made transistors obsolete just like transistors made tubes obsolete, but actually microchips are just mini-circuits which house transistors and a whole lot more--condensers, resistors, etc., so the individual transistors are no longer present in a modern device....some individual units are still used, but most are in the chips). The three lead condenser in your radio may in fact be original. Manufacturers mixed them in here and there and still made use of the paper condensers.
What this condenser could even be, if it is an original, is a bypass/tone condenser. If the center lead connects to the plate of the 12AV6 tube, one lead goes to the 50C5 tube. This is the bypass portion. The other clipped lead may have been connected to B- for a small value tone condenser.
Actually, for plate and grid resistors in the 470K region, a suitable bypass condenser is .01 MFD. Using smaller values will limit your bass response. With higher value resistors, you can get by with smaller value condensers. Actually, some radios do this, which adds sensitivity to the amplifier. Using lower value resistors and higher value condensers, however, tends to add stability to amplifiers. Once you learn a lot more about radios, you can start experimenting in this department, but keep to the original schematic for now.
At any rate, check out this multi-lead ceramic condenser for leakage and shorts. There may be a reason as to why someone clipped that lead. If that section of the condenser is faulty, chances are the other part is, too, though ceramic condensers don't often fail.
The unit can be replaced with any type of non-polarized condenser (non-electrolytic). You can use paper (not recommended, as these have been proven to be unreliable) or ceramic or metalized film. Ceramic and metalized film are superb. Radio Shack carries ceramic condensers that are rated for 500 volts. They carry three values, .01 MFD, .0047 MFD, and .001 MFD. You may use one or two .01 MFD condensers for the bypass condenser. If you use two, parallel them for a total value of .02 MFD. This will add bass response to the radio. However, if bass response is already adequate, and the schematic only calls for a .01 MFD condenser, I strongly recommend that you DO NOT increase the value. Adding additional bass to the amplifier will only cause it to distort more easily on bassy music. You may use a .001 MFD condenser from the 12AV6 plate to B-, which will serve as your tone limiting condenser. The purpose of this condenser is to clip off the extreme high frequency response. If left to pass through, you'll hear a high pitched note similar to that of your television set. This is from the radio frequency which your set receives. Actually you'd never hear that frequency because it's too high, but it's a harmonic. You'll also hear a lot more static without that tone condenser. In almost all radios, that tone condenser never goes above .001 MFD, so don't use a value higher than .001 MFD.
If that multi-lead condenser is in fact a replacement and not an original, there is a slight chance that it is rated for too low of a voltage (lower than the voltages used in your radio). This will also cause distortion in the audio should the condenser break down.
In the end, regardless of whether the condensers in the radio are original or not, you should get a multi-meter from Radio Shack or some other reputable place, and use this to check out all of your condensers. One or more is at fault. Remember to disconnect each that you test. Leaving them in the circuit will give you erroneous readings. A meter from Radio Shack is about $20. If you want a finer meter, you can go for a Simpson 260, which is about $300 or more, but the Radio Shack model is almost as accurate.
Thomas
Thomas