[Elecraft] KPA-1500 Efficiency As A Function of Input Power

[Fred Jensen]

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, k6dgw at foothill.net (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%.
> -----------------------------------------------------------------------
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