Alpha shipped a 6ft length of coax to use between the exciter and the 87A. With
new tubes, the input SWR on all bands should be 1.5 or less. As the 3CX800A7s
hours add up, the tubes gradually require more RF drive for the same output.
Alpha recommends keeping the grid current between 20 and 50 ma. Brand new tubes
will require between in the low 40s to high 30s (watts) at 35 ma of grid
current for full output depending upon band.
Go ahead and use the K3 ATU inline. It's not a problem. But do watch for the
gradually increasing drive and grid current demands of the 87A over time. If
that means keeping the drive down as the tubes age, 1200 vs 1500 watts output
will never be noticed.
With very heavy use, a pair of 3CX800A7s can last 10-12 years.
YMWV.
73 - Steve WB6RSE
On Aug 22, 2012, at 9:28 AM, Mike Wetzel wrote:
80 meters it is 6+ bars (about 2.5 to 1) which seems quite a bit high. I have
tried
other coax lengths and when 80 was ok then 10 meters was high.
Anyone see the same thing and/or have any solutions/suggestions?
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