Can I replace a paper capacitor with a silver mica. The paper one had a value of .0005uf 630v wich is a non-regular part but available in mica.

The original paper cap was rated at 600 but the mica is only at 500, should it be ok or should I use a ceramic cap. This cap goes between pin 2 and 7 of the 7B4 AMP.

Hi, Dave. This cap is going between the plate and cathode, which is severe duty. I wouldn't reduce the rated voltage below that specified.

You can use a 0.001-uF cap, which is readily available in a 630-V rating. Or, you could put two 0.001 caps in series and get 0.0005uF.

:The original paper cap was rated at 600 but the mica is only at 500, should it be ok or should I use a ceramic cap. This cap goes between pin 2 and 7 of the 7B4 AMP.

What about a 1kv ceramic disc 500pf. I have one of those.

Should be fine.

:What about a 1kv ceramic disc 500pf. I have one of those.

500 volt mica will be just fine. What is the maximum voltage in your radio? 300? Unless you get a really nice surge (lightning bolt), it isn't going to arc. Even then, micas rarely short out.

T.

The power transformer on my console puts out 625vac. WOW!! I am more concerned about the function between the original paper cap and a replacement, ie ceramic and Silver mica. Cool think about ceramic is you can get super high voltage ratings in the pf range. Poly films can be a bear to get in those ranges and ratings.

Is that 625 from end to end or 625 from end to center tap? If it's from end to center tap, then the radio itself only uses a total of 312 volts. I highly doubt that your radio uses 625 volts. The total voltage is for each out of phase half of of the high voltage winding, which feeds into a full wave rectifier.

T.

Sorry...made a mistake. This one reads correctly:

:Is that 625 from end to end or 625 from end to center tap? If it's from END TO END, then the radio itself only uses a total of 312 volts. I highly doubt that your radio uses 625 volts. The total voltage is for each out of phase half of of the high voltage winding, which feeds into a full wave rectifier.
:
:T.

Yes, the full secondary is 625vac, center taps are 312 each and aux tap is 7v for lights. Point being is that there are wires in the chassis that are 625 vac (coming out of trnasformer into chassis)

That's not exactly true. All voltage "potential" is measured referenced to "something"... like chassis ground typically.... and in that case, nothing is greater than 312vac in your radio.
Nowhere in your radio is the one end of the 625vac of the secondary ever used relative to the opposite end except where the two ends see the two separate plates of the rectifier inside the tube.
If at that spot you held one end with one hand and then grabbed hold the other with your other hand ... only then would feel the 625v thrill of freshly squeezed electron juice.

So..only If you choose to reference it to the other end of the winding ...then yes you will measure 625v