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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