[Heathkit] SB-220 socket question

[David Thompson]

The Eimac 3-400 and later 3-500 series had two know problems that often
occurred in tubes for no good reason.  Bill Orr W6SAI pointed these out with
suggestion for a fix.

1.    The tubes would go dark and one of the filament pins would unsolder.
This could happen even if the pin of the socket turned out to be OK.  In the
3-400 this also occurred if the tube did not sit well in the socket.  This
occurred mostly in air system sockets with chimney such as in the Henry 2K.
In the 3-500 series the rube also goes dark and again a filament pin
unsolders.  You might have a a bad socket pin but usually you do not.

The fix is to resolder the pin using silver solder and a small portable
torch.  Do not use a regular soldering iron or gun.

2.    The second problem is the grid to plate short.  The only fix is to
apply a capacity high voltage shock to the plate and grid and sometimes (not
always) the short is removed.

Not sure if this continued with later Eimac versions (not made by Eimac).  I
had a pair of 3-500ZG's in my SB-220 and they hummed along OK.

Dave K4JRB