[Amps] What is the best way to run a pair of 4-1000 tubes

[Pat Barthelow]

Another question(s) re 4-1000As.   I see them pretty regularly at  ham swap meets, used  and cheap.  Often with the carbon coated brown "tint" on the inside of the envelope.  Does anyone know what the likely commercial application is/was, that pulls, floating around the ham community were used in?   Military?   Broadcast radio?  What was the Pulse application?
Someone mentioned in the past, that Broadcast TX's that used to yield 4-1000A pulls, have evolved towards solid state finals, and the supply of pulls, has/is drying up.
 Is the carbon deposit an indication of extreme age or hard running, and probable near-end of life issues?   Or, can it exist, and the tube still be used in Amateur Service, happily ever after?  What are the likely failure modes for the 4-1000?

Did the 3-1000Z ever have a commercial application?

If the pulls have been sitting around for years, or decades, are they subject to
the gas ingestion problem across their pin seals, over time of stored, non-operation?   Can you condition them with heat, but reduced B+ to degass them?
I havent looked for one, but is there usually a manufacturer's date code printed somewhere on, or in the tube?

BTW, I have an Eimac, aluminum SK-5??  air blower socket for the tube, surplus to my needs, in case anyone is looking.


Merry Christmas,

All the Best, 73,
Pat Barthelow     aa6eg at hotmail.com
http://www.jamesburgdish.org
Subscribe: http://bambi.net/jamesburg.html
Jamesburg Earth Station  Moon Bounce Team

> From: robby at route2.pe.ca
> To: amps at contesting.com
> Date: Sun, 23 Dec 2007 12:34:06 -0400
> Subject: Re: [Amps] What is the best way to run a pair of 4-1000 tubes
> 
> I built a grounded grid amp a few years ago....um..I guess 20..and used a
> pair of 4-1000PRs.  I built it with RTTY contesting in mind.  I used a
> separate filament transformer and B&W filament choke for each tube and had a
> second blower that could be brought on line for RTTY.  A pair of Hammond 795
> transformers in the P/S. It loafed at the limit on the low bands. 
> 
> Unfortunately, even though I built it in a big box and was very careful
> about stray capacitance in the output, I saw greatly reduced output on 10
> meters and also on 15.  The output capacitance of these tubes is far beyond
> what is necessary to resonate on the upper HF bands and still see the proper
> plate load impedance. 7.6pf per tube for a total of 15.2 on the pair. I
> assume this is because the screen grid is in very close proximity to the
> anode.
> 
> But boy did it like 40M!  It is currently sitting idle at VE7ZZZ. 
> 
> Get a triode if you want a GG amp.  The 3-1000Z has 0.12pf per tube.
> 
> If you are stuck on using the tetrodes, and want 10 and 15 meters I guess
> you need to run them in another configuration. 
> 
> I often wondered what would have happened if I had let the screens float.
> Or tied them to the anode.  Something bad probably.
> 
> -Robby
> VY2SS
> 
> 
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