[AMRadio] Has anyone built a linear using a 6c21

[D. Chester]

Note the modified specs for amateur service using the 6C21.  The original 
specified filament voltage 8.2 volts is for pulse service, and is designed 
for extra emission at the expense of tube life.  The filament is actually 
the same as that of the 450TH/TL, designed to run at 7.5 volts for 
continuous service. Running it at 8.2 volts will substantially and 
unnecessarily shorten the life of the tube.

http://www.lakeerieba.com/6C21/Specs.htm

Don k4kyv