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

[Fred Jensen]

Well, only if you've figured out a way to divide by zero. [:-)

The term "amplifier efficiency" must have changed dramatically since I 
worked in broadcast nearly a lifetime ago.  Then, it was the ratio 
[expressed as a percentage] of the RF power delivered to the 3 1/8" 
hardline divided by the DC power supplied to the amplifier plate 
circuit.  Power to the filaments was generally excluded by manufacturers 
seeking to have higher efficiency numbers.  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%.

To measure the efficiency of a KPA1500 [or 500, or KXPA100, or KPA2] one 
would measure the key down RF output and divide it by the key down DC 
input power.  If it was water-cooled, I suppose one should include the 
input power to the pump(s), but no one ever did.  SS amplifiers like the 
KPA(1)500 probably run class AB<mumble> or its equivalent and have 
substantial DC input power even at zero RF input.

RF output power vs RF input power defines the amplifer's transfer 
function, not its efficiency.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

PS:  I really don't recommend trying to get four parallel 4-1000A's to 
work anything close to "well" at 90.7 MHz. Apparently, it seemed like a 
good idea at the time. [:-)

On 8/17/2018 6:24 AM, Charlie T wrote:
> Think zero output with zero drive = zero efficiency.
> Apply some drive, read some output and the efficiency goes up from there.
>
> 73, Charlie k3ICH
>