[Amps] tetrode vs triode in GG amp TSPA

[John T. M. Lyles]

Sometimes its availability. I am replacing a GG triode amplifier used 
at 200 MHz, with a GG tetrode amplifier. The triode is run near the 
limit of plate dissipation and was designed 50 years ago. The tetrode 
is capable of ~2X as much, having multiphase cooling, and was 
designed 10 years ago. The triode had self bias with a cathode 
resistor. The tetrode requires both a control grid and screen grid 
power supply, as the cavity doesn't lend to cathode resistor anymore 
(different amplifier structure). Price of tubes is comparable, power 
supplies are pretty costly however, as screen voltage is up to 2000 
and screen current is in the Amperes. (10 kW supply!).

For amateur use, triodes in GG are wonderful if you can get them. 
Simple. For class C plate modulated or FM, tetrodes are great too - 
depends on the tube manufacturer as to what is available in many 
cases.

73
John
K5PRO

>
>>  Why do some designers use a triode versus a tetrode for
>>  linear amplifier
>>  finals?  A perfect example is the use of a pair of
>>  3CX800's compared to a
>  > pair of 4CX800's.
>