Paper capacitors.

[Markpab66]

Hello there, got a question for more knowledgeable members. I've taken the base off my Kit 34 amp, just to check the internal condition of parts, and have discovered 4 paper capacitors. They are Jensen 0.22uf 400v mounted under the tag boards, numbered C11/12/13/14, and they connect the ECF80 tubes to g1 of the EL34's.
My question is, being as they are over 20 years old, and are in a very hot environment, would it be wise to change them for some polypropylene caps, or will it be unnecessary? They look fine, but will need a leg unsoldering to check them properly.
Thanks.

[bob orbell]

You either love them or loath them, but you can test for electrical leaking without removing them. Bob

[Markpab66]

What would be the best way to do that , Bob? My ESR meter is hopeless with such low values, would it need powering on with the tubes in with a dummy 8ohm load so I could measure the voltage across them all?

[John Caswell]

The simplest way to check for leakage is as follows,
Identify and disconnect the EL34 g1 end.
Solder a 100k resistor from the disconnected end to chassis earth.
With a meter set to the 1Kv range connect it across the 100K.
Power up and watch the meter, it should initially rise to whatever the ECF80 electrode voltage is and then drop to 0v.
If it drops to 0v all is well, if it shows any signs of a positive voltage then it is electrically leaky and should be changed.
Replacement capacitor type is your choice but the WD SAX types are excellent as are the Sprague "orange drop" types.

John

[Markpab66]

Thanks for the info John. I may be as well just replacing the caps with some that you've recommended, certainly won't do any harm!