I seem to be having a tuning issue with a recently purchased used Centurion.
Specifically, there doesn't seem to be sufficient capacitance in the LOADING
for 40, 80, 160. When tuning I run the LOAD cap up to 10 (MAX) and the
power output has not yet peaked. The worse band is 160. There the 3-500s
get VERY red with light operating. Here is what I have done so far but, in
my opinion, none of this should have been required as the amps do work. I
think mine has an issue.
NOTE 1: A few of my local Ham friends also have Centurion amps and have a
similar issue on 40 mtrs, but for them, 80 and 160 are fine.
NOTE 2: The following tests were all done using resonant antennas. I also
tested the amp on a KW dummy load. The settings were almost exactly the
same.
> I switched locations of the 330pf and 430pf so the 430ph would switch in
for 40 mtrs. 80 and 160 capacitance would stay the same.
- This helped 50 in the CW band LOAD setting of 8.6 was the power
out peak.
- Above 7.2 the LOAD still ran up to 10 and no power peak.
> I added a 150pf in parallel with the 430pf (40 meters FIXED)
- 40 mtrs: Load control now peaks power / dips current on entire range 7.0
- 7.3 on dummy load and antenna
- 430pf + 150pf (represents an increase of 250pf for 40
mtrs)
- LOAD control settings range from 6.1 to 8.4
>I added two 150 pf in caps parallel with the 330pf.
- this brings to total capacitance on 80/160 to 1310 pf - up from 760 pf
- I am now able to tune through a peak power output for the entire range of
80 meters
- LOAD control settings range from 3.2 to 6.0
> I then added one additional 150pf in parallel with the 330pf.
- On 160 the LOAD control still can be turned up to 10 without any power
output peak
- The 3-500s still get VERY red during regular use.
- Part of the 80 mtr band is now below the tuning range for
LOAD, so I removed this additional 150pf cap.
Any suggestions??
73,
Bruce - N1LN
(aka: NC4KW)
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