In article , Frank wrote:

I have the NC-60 open right now and, for what it's worth, National used a
paper cap to couple the 1st audio amp to the power amp. They used a disk
ceramic from the wiper of the volume control to the 1st audio.

The power amp stage has considerable grid capacitance, so the input impedance
is fairly high, and so a larger value cap is needed. The first audio stage
doesn't have so much capacitance, so you can get away with a smaller valued
cap. And the name of the game is to keep costs down.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."