[Amps] 4-1000A Pi-Output-Load-Control & RTTY

[w3hvq]

    Gents/Ladies,
    Just a suggestion if running a 1-1000A and the bright red plate bothers you as it does me.  I know, many think that this tube should always run with a plate red because its built for it.  All I know is that my HB amp's tube is still in perfect condition after 15 years of mostly "black-plate use" here at station W8OHT.
    My suggestion is based on my happy experience in the recent Volta RTTY contest.  For good results in this DX contest, as is in most, almost full RF output is required from the amplifier when using a 4-1000A linear into a poor-man's inverted ell on 40 meters at night, for example.  My tube's biasing is fixed at about 10 vdc as I recall.
    When my homebrewed Pi loading control (ex-HRO-receiver variable with all sections-in-parallel) was set the same for RTTY as for SSB or CW, my tube's plate went from black to full red (not yellow) by the time my longest contest exchange macro had completed its canned message: (his call 599 Q# Q# - 05 05 his-call).  Since I couldn't allow my favorite pet tube to undergo such treatment, I reduced the drive from the K-3 to about 11 watts.  A cheap old RF watt meter on the antenna line indicated about 300 watts to the antenna (with no appreciable reflected power).   Due to noisey nitetime conditions on 40m this output signal was enough to get DX, but only with frequent repeats.
    So I made an effort to see if I could lighten the loading control to result in more RF voltage on the plate of the subject tube and thereby get the same output with less DC plate current.  The HRO loading control had been indicating a reading of 200, but now I could put amplifier in tune and use more drive power (45 watts), yet experienced no RF voltage break downs (frying sounds) in the amplifier's output circuit (the HRO loading dial now indicated 25 (a much higher output pi loading capacity, i.e., lighter loading).  Now turning the tuning capacitor always yielded a much easier-to-adjust dip and there was only slight-redness in the plate at the very end of contest transmissions.   Now the output RF meter indicated 850 watts output to the antenna and the longest sending macro for the contest resulted in plate redness only during the final second of these hundred-percent-duty-cycle transmissions.  So "Mission accomplished". No more contest messages had to be repeated.
FYI,
John, W8OHT