[Boatanchors] 4-1000A coloration ?

[Geoff]

The first step in degassing is to fire up the tube at an anode voltage that 
wont sustain an arc; this is usually about 900-1200V. The grids are tied 
together and grounded and the filament is at 7.5V. Provide operating bias 
that will allow the anode to run at a bright red to dull orange and run the 
tube for as many hours or days it takes....naturally plenty of air and a CCS 
rated PS is required.. If a tube cant be recovered in 1-2 days its ready for 
display or as a lamp.

Finally hi pot the tube and record where it starts to show excessive 
leakage. Since CW and SSB peak voltages are half of 100% modulated AM many 
can run in that service happily for years or decades as long as they get a 
regular dose of good plate color.

If the power out is low possibly running the filament a bit high for 10-15 
minutes will decarburize it but usually its simply a case of a worn out tube 
that was pulled for good reason.

I suspect a good portion of soft tubes are continuously recycled thru 
hamfest and Fleabay and on to a new unsuspecting owner.

The above is applicable to all tubes that have the getter deposited on the 
anode which also includes many graphite ones.

Carl
KM1H


----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Rob Atkinson" <ranchorobbo at gmail.com>; "Jim Wiley" <jwiley at alaska.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Monday, January 02, 2012 5:59 PM
Subject: Re: [Boatanchors] 4-1000A coloration ?


>
> ----- Original Message ----- 
> From: "Rob Atkinson" <ranchorobbo at gmail.com>
> To: "Jim Wiley" <jwiley at alaska.net>
> Cc: <boatanchors at mailman.qth.net>
> Sent: Monday, January 02, 2012 2:05 PM
> Subject: Re: [Boatanchors] 4-1000A coloration ?
>
>
> if you do it right you can degas them.
>
>
> rob
> k5uj
>
>     I am curious what method you use. My understanding is
> that Eimac uses a special vacuum pump to create a very
> thorough vacuum when the tubes are made and uses plate
> material that acts as a getter when running at red heat. If
> my understanding is correct the gas will poison the filament
> so that once a tube becomes gassy running it will destroy
> the emmissivity of the filament even if you manage to run
> the tube hot enough to getter whatever gas there is. Now,
> all this may be wrong so I would like to know. There are
> lots of old transmitting tubes around that are structurally
> OK but gassy.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
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