From: Peter Chadwick <Peter_Chadwick@mitel.com>
First, I agree that receiver intercept is hardly an issue unless
someone leaves a noise blanker on or has too much front end gain.
The largest problem is by far the very very poor transmitter IMD
specs tolerated, and poor operation of conventional linears.
One fellow who LOVES the G2DAF'fy self-biased keeps bugging
Ameritron to build cathode driven tetrodes with the DAF circuit
because they are "good enough for Hams".
The G2DAF design he tested measured about -25 dB below PEP,
which is -19 dB below one tone of a two tone test in a commercial
type test. A standard pair of 3CX800's measures in the -46 dB
range in amateur type testing, and -40 dB or better in normal
testing.
Even 811 tubes pushed to the limit are much cleaner than a
conservative Daffy circuit.
I can see no reason to downgrade the poor IMD standards we
tolerate even more.
> The assumptions made and not stated (something you shouldn't do on this
> reflector!) are that we are talking about an SSB bandwidth, 10dB noise
> figure, and HF operation.
and as proof to that statement, let me keep the spirit going.....
You said:
> triode pushing a couple of watts input. It drifts like Kon Tiki, pulls
> like a Union Pacific Big Boy, has more FM when modulated than KFOX, gives
> hernias when you lift it. But it's good on phase noise.......
The 4-8-8-4 Big Boy's because of its lighter weight on the drivers,
actually had less tractive effort than the Allegheny 2-6-6-6. IMO,
that generator pulls like a Allegheny 2-6-6-6, and weighs almost as
much as one.
By the way, the Big Boy had a problem you may not have heard of.
The basic problem with the Big Boy was a parasitic resonance in
the drivers, causing massive boiler explosions when parked in the
Sun. The root cause was high energy stimulated emission of
steam caused by photon bombardment of the steam recovery
pumps. This caused a sharp peak in pressure, causing the drivers
to ring like a gong. This happened even while the engine was in
standby, with a cold fire box (called a "Hillery" in US railroad slang).
In the 70's USA automobiles were made with recycled steel, some
of which was from the Big Boy drivers. Pinto's used this metal in
gas tanks, and when the car was gently tapped from the rear the
tank would go into an uncontrolled oscillation and explode.
Ford changed the tanks to material recycled from the Allegheny 2-
6-6-6, and that cured the problem. Very few tanks have exploded in
1979 and newer Pinto models. Rumor has it that the side mounted
fuel tanks in GM trucks also used Big Boy driver steel.
73, Tom W8JI
w8ji@contesting.com
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