[Elecraft] Operating with a KXPA100 driving a KPA500

[John Marvin]

Hi,

I've been operating with an OpenHPSDR Hermes driving a KXPA100 for quite 
a while (I ordered my KXPA100 on the day that Elecraft started taking 
orders for it). I just ordered a KPA500/KAT500 combination for higher 
power operation. My plan is to drive the KPA500 from the KXPA100. I know 
that others have done this, but I haven't seen many details.

Since I have an early KXPA100 (Serial #302), it doesn't have the extra 
PTT protection, but I believe that is not a problem with the KPA500, 
since it uses a 5V keying circuit. So I plan to "Y" the PTT connection 
from the Hermes (actually there's some custom mods to provide a little 
more protection for the Hermes on the PTT line, and was also a required 
change to properly key the KXPA100) that currently goes to the KXPA100 
and connect that also to the KAT500. Then I will connect the PTT out 
from the KAT500 to the PTT in on the KPA500. I'll operate the built-in 
KXAT100 in bypass mode when operating with the KPA500.  Are there any 
potential issues I should be looking for? Any timing adjustments that 
can be made?

I know I'll have to do some calibration with the HPSDR software to make 
sure that I don't drive the KXPA100 beyond 30-40 watts when it is 
driving the KPA500. I don't have any way of doing anything with the ALC 
output from the KPA500, so I just need to make sure I don't get it to 
that point.

Eventually I plan to do some better software integration to take better 
advantage of the band switching support, but I've meant to do that for 
some time with the KXPA100 and haven't gotten around to it (so much 
software to write, so little time!). So meanwhile I'll be operating with 
a fairly basic connection setup.

Some questions:

1) Since I don't have a K3, I currently have no need for the AUX 
connector that would normally go between the K3 and the KAT500. Is there 
any advantage/reason to connect an AUX cable between the KAT500 and the 
KPA500? If the KAT500 is basically just looking at the signals from the 
K3 without ever driving anything for the connection to the KPA500, then 
this wouldn't make sense. But if there is any active info being passed, 
perhaps it would make sense? For example, while the KAT500 is tuning it 
can drop PTT to the KPA500, in which case the KPA500 is probably not 
determining the transmit frequency, whereas the KAT500 is looking at 
that. It could tell the KPA500 the correct band rather than having the 
KPA500 determine that by itself. Probably not that important, but 
perhaps I'm missing something.

2) Is there any indication in the KPA500 LCD screen when the ALC is 
triggered? How about the KPA500 utility? I haven't seen anything in the 
documentation, but perhaps I missed that.

3) I ordered both the 120V power cord/fuses and the 240V power 
cord/fuses.  I'm going to start with 120V operation, but I can wire the 
study (my "shack") with a 240V outlet if necessary.
I'm not even sure I can currently dedicate a 120V circuit to the amp, so 
I might have to move to 240V fairly quickly (If I'm going to wire a new 
circuit, might as well be a 240V circuit). For
those running their KPA500's on 120V how well has that worked for you?

4) Anything else that I might have missed? I'm especially interested in 
any operating procedure tips from those who are running with a KXPA100 
driving their KPA500.

5) I read about some earlier issues with the KAT500/KPA500 when tuning, 
i.e. the KPA500 would fault during the tune in some cases. I believe 
that has been fixed in firmware, i.e. I haven't seen any recent reports 
related to this. Can I assume this issue is no longer present?

73,

John
AC0ZG