Yes, it was Class C ... FM is constant envelope modulation. The ancient
50's/60's rules of thumb were:
Class A: 25% - really linear
Class B: 50% - linear with crossover distortion
Class C: 75% - exceedingly non-linear
Class AB1: between A & B, no grid current - mitigates crossover
distortion
Class AB2: AB1 but draws grid current - also mitigates crossover dist.
For audio, Classes B and AB<mumble> needed two tubes and operated push-pull.
We were interested in efficiency of the PA because higher efficiency
meant lower dissipation for a fixed output [10 KW]. As it was, at 90.7
MHz, the anodes were already nearly white. Again ... I do not recommend
using four parallel 4-1000A's anywhere near 90.7 MHz. [:-))
The RCA Ampliphase [aka "Amplifuzz"] series of AM transmitters ran Class
C through the entire RF chain. They were a bear to align ... you never
wanted to start a PoP after sign-off if you'd been awake all day. The
Ampliphase history is moderately interesting however, especially if
you're from or in Sacramento CA.
This thread however has been discussing "efficiency" of a KPA1500 in
terms of output power vs drive power which isn't even remotely close to
measuring efficiency. As amateurs, I can't come up with a single reason
why we'd be concerned about efficiency as long as the amplifier design
is solid and robust. Our A/C uses far more energy over a summer than my
K3/KPA500 did all year, and I leave it on a lot. If this is all about
fans and their noise, the thread needs a new subject.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 8/17/2018 3:06 PM, Bill Frantz wrote:
And I would guess it was running in class C, which is not linear, so
only useful for certain modes (including FM). Class C can convert most
of the input power to RF power.
73 Bill AE6JV
On 8/17/18 at 11:48 AM, [email protected] (Fred Jensen) wrote:
One 10 KW FM transmitter I helped build used four 4-1000A's in
parallel and the filament power was 600 watts. Efficiency, including
filament power was just over 70%.
-----------------------------------------------------------------------
Bill Frantz | Ham radio contesting is a | Periwinkle
(408)356-8506 | contact sport. | 16345 Englewood Ave
www.pwpconsult.com | - Ken Widelitz K6LA / VY2TT | Los Gatos, CA 95032
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