[Boatanchors] 4-1000A coloration ?

[Richard Knoppow]

----- Original Message ----- 
From: "Geoff" <geoffrey at jeremy.mv.com>
To: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
Cc: <boatanchors at mailman.qth.net>
Sent: Monday, January 02, 2012 5:11 PM
Subject: Re: [Boatanchors] 4-1000A coloration ?


> 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

     Thanks. I was familiar with regenerating thoriated 
tungsten filaments by running at higher than normal voltage 
for a time. I think Eimac describes this in one of their 
service notes or booklets. It is the effect of gas on the 
filament I am concerned with but it should be worth trying 
running the tube at red heat for a time to see if it will 
getter the gas.
     While the seals in most transmitting tubes were very 
good almost anything will leak after enough time.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com