John,

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

I've heard very good things about the Ampex variants with the carbon anodes.

Dave Heil K8MN

John N9JG wrote:
I am not sure if the Drake L4-B qualifies as a suitable topic for this
newsgroup, but it does use tubes and the power supply could be used as an
anchor for a small boat.

Are the Chinese 3-500ZGs a drop-in replacement for the Eimac 3-500Z in the
Drake L-4B?

John, N9JG