On HF a 4-1000A should run a good 1.5kW , even more, continuously.
Red glowing plate is normal. In fact when in idle with 5500 V on plate in
GG they glow
brighter than when driven to 1.5kW output. Unless there is some reason why
the efficiency is low, they should operate 24/7 with a full gallon output.
73
Bill wa4lav
At 11:58 AM 5/25/2011 -0400, w3hvq wrote:
> 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
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