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

To: "w3hvq" <w3hvq@frontiernet.net>, <amps@contesting.com>
Subject: Re: [Amps] 4-1000A Pi-Output-Load-Control & RTTY
From: "Carl" <km1h@jeremy.mv.com>
Date: Wed, 25 May 2011 13:37:21 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Since the 4X1 ran with some color 24/7 in an AM and FM BC rigs I wouldnt 
loose sleep over it in less severe intermittent ham use including RTTY. 
Adequate cooling is more important.

Id start by calculating the amps efficiency and if its below 60% then 
correct that problem.

There are plenty of hams running them as an AM linear for 10-20 years with 
no problem and they were pulls to start with.....and a lot more are using 
them on SSB/CW.

Carl
KM1H



----- Original Message ----- 
From: "w3hvq" <w3hvq@frontiernet.net>
To: <amps@contesting.com>
Sent: Wednesday, May 25, 2011 11:58 AM
Subject: [Amps] 4-1000A Pi-Output-Load-Control & RTTY


>    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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