"I have never understood why people did this. If you want a triode, get a
triode. I guess if you have a tetrode lying around taking up space but you
really want a triode it makes sense, sort of, but is there any other
reason?"
I thought that somewhere on my amateur license, or in the rules, there was a
clause that you had to be able to build amplifiers using cheap tubes. I
cannot find that language right at the moment. But, if an 8877 costs $700
and you see a box of 4CX250 tubes sitting at a swap meet with 50 cents per
tube, that seems to be a good reason to think about using the 4CX250. The
reason to use them in some sort of grounded grid configuration, rather than
grounded cathode are numerous:
1. You can eliminate the necessary stabilized screen supply and bias
supply.
2. Grounded grid is more stable
3. Grounded grid is cleaner than grounded cathode (lower imd). This is
relevant since the 4CX250 is not especially clean when operated grounded
cathode.
4. The extra drive power of grounded grid is easily handled by hams with
100 watt rigs.
5/ Some hams like to experiment with unconventional ways of doing things,
especially if it saves lots of money.
73, Colin K7FM
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