Tue, 4 Dec 2001 07:48:43 -0800
> > I got the idea from a very special place :) The tube's Data Sheet that
> > recommends a specific set of operational parameters for SSB AB Class.
> > The output is set at 1500W under these conditions. It somebody is doing
> > more than that it means that they do not respect the manufacturers
> > specifications.
> Quite simply, you received the "FCC version" of the spec sheet! The
> 8877/3CX1500A7 and 3CX800A7 were first being sampled to the amateur
> amplifier manufacturers about the same time as the FCC was adopting new
> type acceptance rules to handle 27 MHz problem and excess power problem.
> In order to avoid redesigning amplifiers (and/or create new tubes) Eimac
> produced new specifications for the tubes which met the type acceptance
> rules for maximum/minimum gain and power output.
[Steve Katz] Not surprised there are marketing variants of data
sheets from Eimac, just like from anyone else. AL1500 runs ~65% efficiency
at full power output, resulting in only about 1200W dissipation at 2250W
output power...well below its dissipation rating. It runs a tad cooler than
in most conventional designs because the "key up" (ZS) dissipation is
reduced to zero (even when the amp T/R relay is in the xmit position, so the
amp is "keyed") by an RF sensing bias circuit, saving about 250-300W of
idling power. If the amp has parasitic problems they haven't surfaced for
me. I would not trust it to run >1.5kW full-carrier mode (RTTY, FM), but
for SSB and CW operation it appears conservative at >>1.5kW output. As with
most linear amplifiers, efficiency falls with output power, so it's most
efficient when run at >1.5kW.
> The 8877 will easily produce 2500 watts output at 100 MHz in class C
> service (I also ran an FM transmitter with one at my first station out
> of college). With proper plate voltage and bias, at 30 MHz the 8877
> in class AB2 should easily produce much more than the "amateur" specs!
> ... Joe, K4IK
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