[Heathkit] reactivation of a 3-500

[David Thompson]

I was always under the impression that a gas filled tube was done for . 
Both the 3-400 and 3-500 Eimac did have a problem with the filaments 
unsoldering and going dark.  Checking the filaments, at least one pin had 
become unsoldered.  This can be corrected by using a soldering type blow 
torch and good silver solder.  The cause was a loose connection in the tube 
socket.  This can be corrected by tightening the connector for the pin in 
the tube socket.  I had problems with wind blowing up from underneath in my 
Henry 2K Amp and that lifted the tube out of the socket.  Pushing the tube 
back into the socket cured the problem unless the filament pin had become 
unsoldered.  This was specific to 3-400's.  But I had the same problem with 
a 3-500Z in an Amp Supply LK-500

One other problem that "could" be cured was the grid plate short.  Jim K4DLI 
who was with Varian at the time could use his test gear to pop a charge into 
the tube that might get rid of the short.  Bill W6SAI wrote a couple of 
articles in CQ and ham radio magazines talking about these cures.  I never 
saw him mention fixing a glassy tube.

The Eimac papers I had on the Care and Feeding of Eimac tubes all covered 
the 4-125 to 4-400 series (all wriiten by W6SAI).  I ran a 4-400A amp for 
years with none of these problems.

73 Dave K4JRB