Quoting Vic K2VCO <k2vco.vic@gmail.com>:
If I had it to do over again, I think I would use a triode!
Nothing wrong with a triode, but you can have more control with a tetrode.
Working with a 4cx12,000 last night, I noticed that with zero screen
voltage the transmitter was able to make around 10% rated power output.
Add a little voltage with the screen variac, and it smoothly rises to 125%
with no more than 50ma screen current at any point.
The 4CX20,000s are even better at making power with low screen current.
The 1000s are much more temperamental, but the small pentodes ... the 5cx1500s
will make 2.2kw dc carrier in FM service 24/7 for 18 months or more.
Swap out the 4cx1000 for a 5cx1500, and in ham service, it could be
your last tube.
Don W4DNR
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