[Amps] triode vs tetrode

[Rex Greenwell]

Eimac had a bulletin out describing the 4-1000A tetrode in grounded 
grid, it states  "Most tetrodes do not perform satisfactorily when 
connected as a high-mu triodes.  Control grid dissipation usually limits 
their power handling capability when they are connected in this 
manner.   The 4-1000A is an exception to this rule if a plate voltage of 
at least 3000 volts is used. " With a plate voltage above 3000 volts a 
4-1000A is a legal limit plus amplifier in grounded grid.  I can supply 
a pdf of this bulletin should anyone desire.

It has long been known that 4-400 tetrodes operate satisfactorily in 
grounded grid as well.  They will plug-in replace 3-500Z finals in the 
SB-220 and variant amplifiers when all of the grid pins on the sockets 
are connected directly to ground with low inductance leads.  This is how 
the 3-500Z tube sockets should be wired in any event whether to use 
4-400s as finals or not.   The original SB-220 and other designs using 
RF chokes and bypass caps on the grid leads proved to be a poor idea.

K0KP