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

To: w3hvq <w3hvq@frontiernet.net>, "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] 4-1000A Pi-Output-Load-Control & RTTY
From: Bill Fuqua <wlfuqu00@uky.edu>
Date: Wed, 25 May 2011 15:04:08 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
    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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