[Boatanchors] 4-1000A coloration ?

[Geoff]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Geoff" <geoffrey at jeremy.mv.com>
Cc: <boatanchors at mailman.qth.net>
Sent: Monday, January 02, 2012 8:43 PM
Subject: Re: [Boatanchors] 4-1000A coloration ?


>
> ----- 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


Ive yet to find a TX tube filament that was affected just by outgassing 
which has nothing to do with tube seals. If air has made its way in then the 
filament is likely already poisoned depending upon the amount.

The single biggest cause of filament carburization is operating at under 
voltage.

Carl
KM1H