[Elecraft] Does KPA1500 have these KPA500 characteristics?

[Bob McGraw K4TAX]

Eric, et & al:

I have a KPA500 on the desk.  It is about 1 month old.   As to 
efficiency which is related to power output vs. power input, a simple 
ohms law calculation is all that's needed to see what is occurring.   
During transmit, note the value of HV and the value of CURRENT.  Also 
note the power output in watts.   All of these values are on the LCD 
display.     Per Ohms law, Volts x Current = watts which is DC watts 
input.   Then Power output ÷ DC watts input X 100 = % efficiency.

With my amp in CW mode key down on 80M:   Voltage = 63.0, Current = 12.1 
amps, RF power output is 575 watts.   Thus 63.0 x 12.1 = 762.3 watts DC 
power input.    Then 575/763.3 = .7533 x 100 = 75.33%.      In this 
configuration 762.3 - 575 = 187.3 watts of required heat dissipation.

Now at a lower power output on 80M:  Voltage is 64.6, Current is 8.8 
amps, RF power output is 300 watts.   Thus 64.6 x 8.8 = 568.5 watts DC 
power input.   Then 300/568.5 = .5277 x 100 = 52.77% In this 
configuration 268.5 watts of required heat dissipation.

My power measurements are made using my Bird 43 and a 50.5 ohm dummy 
load.   I have not done a calibration on the KPA500 power meter, 
although I find it relatively accurate.

Now in each case, the difference between RF power output and DC power 
input is the watts of heat that will be dissipated.  Yes, it is clear 
that running the amp at higher power, but never to exceed the rating nor 
temperature limits is the more efficient method. By the way, those hams 
that run their tube amps at reduced power "to save the tubes" are in 
fact doing just the opposite in as much as the efficiency at lower power 
is less than at higher power. The heat has to go somewhere and it ends 
up in the amp or being exhausted by the cooling system.

As to running the amp at 500 watts, or 600 watts or 700 watts, thus just 
before fault power, I would need to examine the IMD products to be 
confident the amp is "clean".  A solid state amp which is being over 
driven just a wee bit can get really nasty on the air and real fast.  
The product is splatter on either side of the operating frequency.   
Avoid this and sacrifice a few watts of output power.

As to the KPA1500, I have no experience or knowledge.  But I would say 
it follows the same rational of operating and efficiency.

73

Bob, K4TAX


On 5/24/2018 7:54 PM, eric norris via Elecraft wrote:
> While trying to run my KPA500 at full-tilt--but as cool as possible--in digital modes, I have noticed over the years that:
> 1). The KPA500 actually runs cooler at just-below-fault power output than it does at either 500 or even 400 watts output.
> 2)  The KPA500 runs substanitally cooler at a 1:1 SWR than it does at even 1.2:1.
> Does the KPA1500 also do this?  I'd appreciate actual experience more  than conjecture.
> Thanks and 73,
> Eric WD6DBM
>
> Sent from Yahoo Mail on Android
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