They are direct replacements but they aren't very good. K3FK had a =
QRO=20
amp with a pair of 'em a few years back and we had to resolder =
filament=20
pins on one or the other of the bottles several times. We dropped in =
a=20
set of Eimacs and the problem went away.

I had the same problem with an Eimac 3-500Z, though once only.

Tony, I0JX