I purchased a recently built K2/100 this summer and am
gradually working my way through careful evaluations.
Today I checked the key-down current and found some
variations that look rather like those mentioned in
Builder Alert #22a. Here are the current readings in
amps, at 75 and 100 watts requested output, on CW,
after allowing the power control loop to settle:
MHz 75 W 100 W
3.5 15 17.5
7 13 15
10 14 16.5
14 13 15.5
18 17 (not tested to avoid blowing 20A fuse)
21 16 19
24 15 17
28 15 18
I observed noticeably high current on 18 and 21 MHz,
as opposed to 14 and 18 MHz as indicated in the
Builder Alert. On the other hand, when I looked at
the current indicated on the K2 display (which should
give an indication of drive power to the PA) I got (in
amps, for 75 watts output requested):
MHz K2 Display Current
3.5 1.38
7 1.44
10 1.44
14 1.98
18 2.00
21 1.58
24 1.66
28 1.62
This looks exactly like the low gain situation
indicated in the Builder Alert.
The supply voltage for these tests, indicated on the
K2 display (key down at 17.5 A), was 13.0 V.
It looks to me like I have a borderline case of the
resistor problem described in the Builder Alert. I
assume the original builder did not know about this
issue as I bought the rig before the Alert came out.
Do you think it would be useful to make the upgrade to
get it working as well as it can ? Has anyone else
observed if the current on 15m is also affected by the
resistor problem or is the higher current I observed
there likely due to something else ? Has anyone got
similar current data before and after making the
Builder Alert 22a upgrade ?
73,
Steve VE3SMA
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