[R-390] Re: Tube Bulb Temperatures

[Drew Papanek]

Hello All,

On the subject of tube temperature vs failure:

There is a temperature-dependent outgassing of the tube elements to 
consider.   Tubes are baked  before and during evacuation to drive out 
residual gases but that takes time and time is money.
Manufacturers hence will tend to bake as little as possible.  We as users 
then bake the tubes by simply using them.   The hotter we run them  the 
greater the outgassing and no vacuum pump for removal.

Nolan's Zippo trick can revive some of these casualties by reactivation of  
the tube's getter.

Water vapor is a particularly egregious offender,  bombarding the cathode 
and causing deterioration.
The getter is not  effective in trapping those trace amounts of water.

On emissivity, that which emits also absorbs.   Place a hot surface (the 
envelope) in proximity to another (the anode) and the latter will run at a 
higher temperature than it otherwise would.

Count me in as a real "fan" of the idea of forced convection cooling!

Yes, as Bob said, we are awash in tubes.   With the severe paucity of 
younger membership in the boatanchor hobby the supply to demand ratio for 
tubes will only improve as we oldsters die out.

New carbon composition resistors (Xicon) were still available from Mouser as 
of recent.

Drew

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