Jim, NN7K wrote:
"---that center conductor of RG-8 was used as Power supply for lots of
AMPS! 3 and 4 KV in some of those."

Nothing wrong with that if the right RG-8 is used. RMS Max V varies from
600 V to 3700 V (Belden 9914). Peak a-c or d-c max V should be 5232 V
for the Belden cable. This is 1.414 X the rms volts. No need to
speculate. Coax tables abound. One is found in the ARRL Antenna Book.

Best regards, Richard Harrison, KB5WZI