> plan to remove the 8875's and install 3cx800.
> Before I begin the operation, any useful remarks??
> Anything I should be aware of on the 3cx800?
Make sure you have adequate airflow to properly cool the tube. Inadequate
cooling and overdriving the 8875s is usually why they go soft. I put a
pair of 3CX800s in my 2500 last fall - works real good! A plenum box was
used to redirect the airflow (similar to the Communications Quarterly
article for using a pair of Svetlana tetrodes). For about the same cost,
the amp has new tubes with about 2.5 times the plate dissipation compared
to the 8875s. Besides the airflow, the only significant mod was rewiring
the tube sockets for the proper 3CX800 heater voltage.
The smoke test for this amp was a serious multi-single effort in the 1996
CQWW CW (J6DX) where it was used on the run station. Except for a slight
buzzing from the transformer when it got a little too warm, the amp performed
flawlessly for 48 straight hours at full output. If I find time (and
space) I may add another small fan to help cool the transformer.
Even a single 3CX800 should work pretty well - better than the 8875s in my
opinion because of the greater plate dissipation when properly cooled.
Good luck,
Steve
--
Steve Miller N8SM millersg@dma.org http://www.dma.org/~millersg
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|