Hello Conrad,
You are right.
Grounding the screen may be the best for stability, this was used for
some commercial amps also (the Collins 30S maybe, 4CX1000 or 1500B).
I don't have details from that ARRL 4CX1000 VHF amp, but I know
about the 3CX1500 2m one. The PTFE sandwich may be attractive
to some, at least regarding the mechanical work needed.
I had some doubts, because the GU43B is specified up to 100 MHz
only, even if it have a coaxial base and socket. A higher freq and lower
power GU34 version exist. This is the first GU43 2m amp I saw.
It seems that from all of the 1 kw tetrodes, the GU43 is the cheapest,
have the lowest cost/watt ratio and it is easy to find, as it was used for
some russian millitary and commercially amps (R-140, Snejinka, etc.)
and I think that the GU43 spare stock was not low.
It have a rather big anode cooler for a 1k tetrode with larger fins spacing
which may translate as a easier cooling, and most GU43 HM amps use
a 5" axial fan for this (which I still don't like).
The main problem is the original coaxial socket which is not so easy to
find and the OM from OK solved this dificult problem also.
This is why this amp have atracted my attention, at the first sight.
Regarding the flashover, from all of the amp work, the "bang" and the
flashover are the things that will be always remembered, is it?
I know this from my personal experience hi, hi ...
thanks,
73,
Traian
G0RUZ Conrad wrote:
> Yes its a copy of the 4CX1000A amplifier that was published in the ARRL
> handbook. I have built this amp and used a 4CX1500B in it, the key is to
> ground the screen. One other caveat is that there is a strange mode set up
> in the anode compartment. I cured it by placing a big (100w) 120 ohm carbon
> resistor stood off the chassis two insulators. I had seen this in some Band
> II cavity amplifiers and it completely cured it, I was astonished at the
> time.
>
> A far better prospect is to use a 1/2wl line over the anode cooler similar
> to this:
>
> http://www.nd2x.net/OH3AWW.html
>
> No nasty PTFE sandwiches to flashover and really good efficiency. I would
> still ground the screen and operate the cathode and g1 at minus g2
> potential.
>
> 73
>
> Conrad G0RUZ
>
> > -----Original Message-----
> > From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> > Behalf Of Traian
> > Sent: 26 October 2004 16:38
> > To: amps@contesting.com
> > Subject: [Amps] GU43B amp for 2m ?
> >
> >
> > Hi all,
> >
> > Pictures from a VHF amp using the GU43B tetrode:
> >
> > http://www.ok1kvk.net/pa_gu43b.htm
> >
> > I like the HM socket, the way how the use of a hard to find socket was
> > avoided.
> > May this to be a 2m amp, as I think?!
> >
> > 73,
> > Traian
> >
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> >
> >
>
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