Rich said:
"It seems a bit doubtful that the 4CX1000A has c. 100-times as much 3rd
order distortion as a 4CX1500B"
The data I mentioned regarding the 4CX1000 and the 4CX1500 comes from:
Care and Feeding of Power Grid Tubes copyright 1967 by Varian - Thrid
Printing 1978.
On page 64, under the heading 4.3 "Selection of Tubes for Single Sideband
Service", it is stated that "As a guide in selecting tubes for various power
levels of single-sideband service, typical operating conditions for various
EIMAC tubes are included in this section. ... Typical third and fifth-order
intermodulation distortion product levels for maximum drive conditions are
also given for the two-tone condition.
In the "guide", I found the following information.
4CX1000A/K @3000 volts yields -23 db 3rd order and -26 db 5th order
distortion
4CX1500B @ 2900 volts yields -44 3rd order and -48 db 5th order distortion.
I did not make this stuff up, Rich. I just reported it. Don't shoot the
messenger if the data does not fall into line with your preconceived notion
of reality.
On page 22.52 of the 23rd Radio Handbook, edited by William I. Orr, there is
a 4CX1500B amplifier construction article. In that article, the following
language appears: "The linear amplifier described in this section is a
deluxe 2-kw PEP, class AB2 grid-driven amplifier using the low distortion
4CX1500B tube. This is a ceramic-metal, forced-air cooled tetrode having a
maximum plate dissipation of 1500 watts. It is designed for exceptionally
low intermodulation in SSB service."
I knew one ham who ran a 4CX1500B and it was the cleanest amp I ever heard.
I just wish a local ham - who runs a 4-1000 driven by an overdriven SB-200,
ran a 4CX1500B operated properly. Unfortunately, my antenna is larger and
taller and his only way to combat that is to turn up his mike gain. I
expect he has had splatter reports from at least 100 countries - which would
entitle him to the coveted DXCCS award.
73, Colin K7FM
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