[Amps] GS-35B Vertical Mounting & Input Impedance

[k7rdx]

Does anyone have any history on the GS-7b? I have a few here and have been
testing them in one of the decks I built for a Op here.. The tube I was told
has close specs to GS-35b and from our testing (On hf) Seems to run cooler
and requires somewhat less drive for similar power output. Any of you guys
in Europe know the origional intent for this tube? Military version of
GS-35b?Thanks, Jim K7RDX..
----- Original Message ----- 
From: "GM3SEK" <gm3sek at ifwtech.co.uk>
To: <amps at contesting.com>
Sent: Thursday, January 12, 2006 12:01 AM
Subject: Re: [Amps] GS-35B Vertical Mounting & Input Impedance


> Steve Thompson wrote:
> >
> > Mike wrote:
> >
> >>Hello,
> >>
> >>Is it okay to use the GS-35B in an upside down, vertical
> >>position?
> >
> >
> > Yes - assuming it's not full of loose stuff.
> >
> That's OK - the GS35 has an internal sieve:
> http://www.pa3csg.hoeplakee.nl/tubes/tubes.html
>
> Most transmitting tubes have the heater/cathode in the middle and the
> anode around the outside. The GS35, GS31 and GI7 are not like that: they
> are UHF-style planar triodes with a flat disk-shaped oxide cathode, a
> domed mesh grid like a small tea-strainer, and a slightly dished copper
> anode. Electrons are emitted across the whole circular area of the
> cathode, come up through the grid and hit the anode. This construction
> gives a very short transit time which is important at UHF.
>
> It also allows the tube to be operated in any orientation and even under
> quite high G forces in airborne equipment. (How they ever lift that lump
> of copper off the runway is a totally different question.)
>
> If you're looking at the photographs, note the reinforcing bars to
> prevent the grid from flexing as it gets hot and expands. Also note the
> extremely effective grounding of the grid, which makes for high
> stability - no long, inductive grid leads here!
>
> You can also see several arc marks on the grid and anode, which PA3CSG
> says are due to that particular tube having been operated at 4kV+. Some
> GS35s will operate fine at higher voltages, but this particular one
> didn't like it and arced repeatedly. In more highly magnified versions
> of those pictures, it is possible to confirm that each arc mark on the
> grid is matched by an arc on the anode. The biggest of these arcs have
> gone through the grid and burned the cathode.
>
> Steve was making a serious point: if there is any loose cathode material
> sitting on the grid, it can emit electrons if the grid becomes hot.
> However, a good tube should have no problems with being operated
> upside-down. The main reason why they don't normally design an amplifier
> that way is not the tube, but the problem of blowing hot air out into
> the small gap between the base of the cabinet and the desk.
>
>
>
> 73 from
> Ian GM3SEK
>
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