I have had the filament unsolder to Eimacs in several amps. W6SAI pointed
out the problem in both the 3-400 and 3-500's. My old Henry 2K had the
problem years ago with a 3-400Z. Last year I had problems with Eimac
3-500Z's in my LK-500NTC.

If the tube socket loses its spring grip the filament does not make good
contact and loses its solder. In The Henry, the tube often just popped out
of the socket, With the LK500NTC I still don;t know what the problem is but
suspect the filament transformer may not be balanced so one tube draws too
much current or even the voltage my be say 4V to one tube and 6 violts to
the other rather than 5V to both. The tube is solid in the socket!

To fix YOU MUST use silver solder and a torch. No soldering iron or gun
will do the job!

Dave K4JRB