[Elecraft] Current requirements for KPA100?

[Bill Coleman]

During a recent contest, I received a report of poor signal quality on 
my CW signal on 80m.

I've run some tests and find that on 80m and 160m, there's a distinct 
hum on the signal when running over about 80 watts. I've also noticed 
that the current used seems to jump in discrete steps as I increase the 
power level. It could be that this hum is present on the power supply 
at higher current levels. On 160m, the rig pegs the scale on my power 
supply ammeter when running full power.

Do the current requirements of the KPA100 increase on these bands? And 
what would cause the discrete steps in current consumption at the 
higher power levels? We're talking a jump in current about every 10 
watts or so.

Prior to the contest, I performed the KPA100 modifications for high SWR 
operation and installed the new firmware. I've noticed that the heat 
sink is running noticeably hotter than before. This while transmitting 
into a 50 ohm dummy load.

Any suggestions would be appreciated. The rig appears to operate just 
fine, I'm just a little concerned about the signal quality and the 
extra heat.


Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901