Hi Keith, many, if not most, engineering decisions are $$ based. A source
of cheap 4CX800 tubes from Russia could cause a company to use them instead of
expensive 3CX800 tubes in an amplifier design for example.
The tetrode tube has to be cheap enough that the cost of the screen supply
and tube socket has to be more than covered by the cost savings.
Performance wise, the cathode driven triode will typically have lower imd
than the grid driven tetrode (due to the heavy negative feedback).
Where the tetrode has an advantage is in the rare case that one wants to use
very low drive power, such as a few watts from a QRP transmitter. The input
grid circuit can be designed to allow full output power with very low drive
power levels. The FCC will not bless a commercial amplifier like this as the
rules don't allow such a design.
73,
Gerald K5GW
In a message dated 4/26/2007 11:16:22 A.M. Central Daylight Time,
kdutson@sbcglobal.net writes:
Something that has been bugging me...
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.
Thanks and 73,
Keith NM5G
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