In the latest issue of the Brittish ELECTRONICS WORLD (11/2000) there is an
interesting article called " NEW LIFE FOR OLD VALVES" where the author
actually accelerated the gettering process by a factor of five by putting
small tubes ( valves,hi ) in an 120C oven for 12hours. As I understand it
he could reduce the gas grid current for lower input noise in small signal
tubes used at low signal levels such as microphone input.
So, could this be applied in a 3-500Z by increasing the temperature even
further? Very nice methode then in the Swedish climate where the
temperature sometimes goes down to very low levels. My flat needs that
additional heat then, hi!
Prosit de Hans SM5KI
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>Från: Pete Smith <n4zr@contesting.com>
>Till: amps@contesting.com
>Ämne: Re: [AMPS] advice on an old SB-220
>Datum: fre 10 nov 2000 23.16
>
>
>At 04:54 PM 11/10/00 -0500, Chuck Counselman wrote:
>...
>>This is as much a question as an answer, but FWIW:
>>
>>I know nothing about 3-500Z's, but a close friend and co-worker
>>successfully degassed quite a few 50-year-old (WW II vintage) 807's and
>>other relatively small tubes by letting them run with (controlled) plate
>>current. First he ran them with just their cathodes heated; but nothing
>>happened. Then he applied B+ (a few hundred volts) and adjusted the grid
>>bias to set the plate power dissipation to a healthy but safe level -- and
>>the tubes degassed themselves within a day or two IIRC. Whether this
>>technique will work with a 3-500Z, I don't know. Perhaps in an 807 the
>>gettering material is applied to the plate, so it works when the plate is
>>hot. I have no idea how a 3-500Z is gettered. Is its plate metal? Is the
>>outside of the plate gray? If so, that might be a getter.
>
>It's been recently said on this reflector (and not contradicted, which may
>be almost a first!), that the gettering material in 3-500s is on the plate,
>and that the plate must show slight color for the gettering process to
>work. If these tubes are severely gassy, it could be a delicate process of
>ramping up the plate voltage, adjusting the bias for just a bit of color,
>waiting a while, ramping up a little more, and so on. surely adding a
>glitch resistor in series with the +B would be a good idea regardless, to
>limit current through any arc that occurs.
>
>
>73, Pete Smith N4ZR
>
>Contesting is ... Extreme Radio
>
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>http://www.qsl.net/n4zr
>
>
>
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