K3 erratic power output

[Al Van Buren]

Hello All,
  I just received K3 kit serial # 1253 with KPA3, KBPF3, KXV3 and
KUSB options.  The kit was very well thought out and was a pleasure
to assemble.  It went together in under 8 hours.  Everything
seemed to calibrate well and work perfectly except for the 100 watt
PA.  When running 12 watts or less (8 watts on 6m) output is good and
 stable.  When power is set higher which causes the 100 W PA to turn
on, output power is not stable.  On 20m thru 6m with key down the  
power output takes about 6 or 7 seconds to stablize.  For example,
when the power control is set for 50 watts it first comes up to 35
watts, then slowly goes up to 60 or 70 watts, then slowly comes down
to 50 watts where is is stable.  It seems like the power control
zero's in on the correct power but very slowly.  With CW it never
gets there. This happens every time the key is opened and then closed
 again.  On 40m the same thing happens but there is about a 3 second
delay after key closure before any output is seen.  There is no power
 output at all on 80m and 160m even though with less than 12 watts
set on the power control there is normal power output. I haven't had
the time to look into the schematic yet so thought I'd see if any of
the list readers have had a similar experience or may have some idea
of a good place to start.    Thanks, Al K7CA
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[GW0ETF]

k7ca wrote

Hello All,
  I just received K3 kit serial # 1253 with KPA3, KBPF3, KXV3 and
KUSB options.  The kit was very well thought out and was a pleasure
to assemble.  It went together in under 8 hours.  Everything
seemed to calibrate well and work perfectly except for the 100 watt
PA.  When running 12 watts or less (8 watts on 6m) output is good and
 stable.  When power is set higher which causes the 100 W PA to turn
on, output power is not stable.  On 20m thru 6m with key down the  
power output takes about 6 or 7 seconds to stablize.  For example,
when the power control is set for 50 watts it first comes up to 35
watts, then slowly goes up to 60 or 70 watts, then slowly comes down
to 50 watts where is is stable.  It seems like the power control
zero's in on the correct power but very slowly.  With CW it never
gets there. This happens every time the key is opened and then closed
 again.  On 40m the same thing happens but there is about a 3 second
delay after key closure before any output is seen.  There is no power
 output at all on 80m and 160m even though with less than 12 watts
set on the power control there is normal power output. I haven't had
the time to look into the schematic yet so thought I'd see if any of
the list readers have had a similar experience or may have some idea
of a good place to start.    Thanks, Al K7CA

Al,

There have been posts previously about erratic power output but maybe not describing such an extreme situation as yours - no output (high) at all on some bands suggests something more serious than erratic power control....:-(

I have occasionally found the power output to suddenly start changing (CW) but it has happened only rarely and never sure if it is connected to a software upgrade or not. Mostly it manifests in the power indication dropping from the '100 watt' level to anything from 35 watts to 80 but it always seems to recover quickly; it is a genuine power variation as checked against an external power meter. Once when I was using my amp it went the other way and increased up towards full power which meant I was briefly knocking out about 1200 watts - I wondered whether Elecraft would bail me out if a man in a grey suit came knocking complaining about me operating outside my licence conditions...:-)

It happened again fairly recently and I went back to the last full firmware version (2.02 I think....) and I've not noticed it since. I'm not convinced though that it is linked to software but I've not even thought about hardware yet 'cos I'm waiting for a KRX3 which will involve some dismantling and checking of connections etc.

Can't be a widespread problem though in view of the dearth of posts on this but it does seem to exist and hopefully if it is a 'real' problem compared to dodgy contacts somewhere, it will be resolved soon. I do wonder if the lack of reporting is because of the fact that it will be much more obvious in CW and may well go unnoticed in ssb.

Good luck,

Stewart Rolfe, GW0ETF (K3/100 145)