All I ever see for Pi coils is cylindrically wound single layer. I
remember when I built my first 6146A output cw transmitter back 40 yrs
ago, I used a B&W pre made coil for the Pi.

Depending on the Q and plate resistance you see coils for multi band
use up to 33 uh, in transmitters.

The only place I see pancake coils used is in Tesla coils, one of
which I built with a pre made 18" tall secondary coil. I wound my own
primary pancake coil.

Done right a pancake coil takes up alot less room than a cylindrically
wound coil.

A six inch diameter pancake coil can have the same inductance as a
three inch diameter by six inch long coil with the same size wire.

Anybody know why I shouldn't use a pancake coil in my final? I just
bought a 4-1000A. from ebay.

73
n8zu