For reference purposes, here are the Communication Quarterly and KU7G
articles (Adobe Acrobat)
regarding 4CX400a or 4CX800a conversions
http://www.tomstubes.com/images/mla_2500_4cx400a.pdf

KU7G
http://www.tomstubes.com/images/mla2500_4cx800a.pdf

w9gb


Hi, Thanks for the excellent links. I had seen the first one before. In
looking at the article about the 2 times 4cx400a, it jumps out at me that
this conversion leads to about 350-500 watts less RF output than original
(1100-1300 versus 750-800) even when using tubes with more capability. I
attribute this to running Tetrodes at low plate voltage. In this application
Hi-Mu Triodes are a better choice. Also the low RF drive need for the
Tetrodes make them attractive for low power exciters, and a problem for us
with a 100 watt exciter.

My conversion is similar to the 4cx800 article except I am using a 8877. I
use the same external box to house the socket, and mount the fan. The 8877
may not be designed for use at 1700 volts, but what the heck, I only want
about 1000 watt RF output. I need a chimney like what is described for tthe
PI-Network he 4cx800. Any idea where I can get a block of Teflon, and then
get it machined?

That article about the 4cx800 has some good visuals of the pi-net that is
being a problem with my 2500.

Thanks again,

Jim
WD5JKO