[Elecraft] KPA500 questions

[Ron D'Eau Claire]

Hi Sebastian:

The actual (maximum) output power is >500 watts on all bands as measured on
a calibrated external wattmeter. I don't operate "all knobs right" so I
haven't pushed it to the limit. (BTW, the internal meter is quite good.)

The power output does not depend upon mode. It'll run 500 watts, minimum, in
any mode.

You can get at least 500 watts on all bands with a good mains supply. When
running the amp from a marginal 120VAC mains that sags too much under full
load, the output on 6 meters may be very close to or slightly under 500
watts. The power supply is not regulated, so it's a matter of setting power
supply taps during initial setup that produce the correct voltage for a
given Mains voltage. If the mains voltage sags too much under full load (6
meters is the band where the KPA draws the most current), it may drop the
voltage so much it limits the KPA500 output. This is NOT an issue with a
good 120V or 240V mains supply. 

The overall gain of the KPA500 varies from band to band, as reflected in the
varying drive levels needed for each band. The K3 offers the ability to set
the drive 'per-band' so the KPA500 automatically comes up at 500 watts (or
whatever you preset) on each band without further adjustment. 

If you use the optional interface cable between the K3 and the KPA500, the
K3 will switch between the correct drive level when the KPA500 is in OPERATE
and another preset level (i.e. 100 watts) when the KPA500 is in STANDBY. 

The KPA500 will run 500 watts on 30 meters. It's up to the Ham to set that
band for no more than 200 watts to be legal. 

If the SWR is above about 2:1, the KPA500 reduces output power to protect
itself and signals a "fault" condition with a flashing light and a message
on the LCD. This reduction is done by inserting an attenuator at the input,
so it's a sudden step, but not all the way back to the drive level. IIRC,
it's about a 3 dB drop in output. If you have a really high SWR (e.g. open
antenna port) the amp will automatically switch to STBY with a HIGH SWR
fault display. 

I don't run WSJT, but that's a 50% duty cycle so the KPA500 should be able
to handle it for much longer than 10 minutes at a time. Perhaps someone with
WSJT experience can elaborate. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Sebastian, W4AS
Sent: Monday, November 14, 2011 1:16 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KPA500 questions

As a potential future buyer of the KPA500, I have a few questions, for those
who actually own it:

What have you found to be the actual output power, on a dummy load using a
good power meter other than the internal one. 

Is the maximum output the same on all modes (CW/AM/FM etc.)?

Is the maximum output the same on all bands (what happens on 30 meters)?

In the event of a high SWR, does the output begin to drop progressively,
and/or does it just stop at some point?  What is the typical SWR that will
keep it happy at full output (without getting into a discussion of resonance
and actual power out the antenna)?

Finally, I read about the duty cycle of 10 minutes on and 5 minutes off, and
I still wonder how it would keep it up with modes such as WSJT, where there
is typically 30 seconds on and 30 seconds off?

73 de Sebastian, W4AS