[Elecraft] K3 Amplifier Drive Inconsistency

[donovanf at starpower.net]

Hi Bill, 


I've never experienced your reported amplifier drive problem with 
my K3 s/n #6100 driving 20 watts into my Lunar Link LA-62 
1500 watt output 6 meter amplifier. Perhaps it unique to the 
K3 - KPA1500 combination. 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Bill Schwantes" <bill4070 at gmail.com> 
To: elecraft at mailman.qth.net 
Sent: Monday, August 5, 2019 11:24:54 PM 
Subject: [Elecraft] K3 Amplifier Drive Inconsistency 

I need help solving an amplifier drive inconsistency problem when I operate 
using digital modes on 50 MHz. I noticed during a recent contest that the 
K3 will sometimes key the amplifier but provide zero drive. I'm using K3 SN 
669 on 50 MHz FT8, FT4 and MSK 144 and driving a KPA1500 to about 750 watts. 

After several consecutive transmissions I notice that the amplifier 
responds briefly to being keyed but the power drops to zero. It's keyed up 
but has no output. The K3's output (drive) is set at 17 watts but there is 
no output on the RF meter when this happens. The K3's red TX indicator is 
on. This problem also occurs when driving a KPA500, though less often 

I can correct this problem temporarily by switching the amplifier to 
standby, which allows the K3 to change to "barefoot" output then switch 
the amplifier back to "operate" which changes drive power back to it's 
preset level. That's usually good for a dozen or so transmit cycles before 
the problem reappears. 

This problem does not occur when driving other amplifiers; nor does it 
occur when using CW or SSB modes. It seems to have something to do with the 
K3/KPA1500 command interface controlling the output power of the K3. 

Any ideas? 

73 Bill W7QQ 
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