On Thu, 2008-06-12 at 17:12 -0400, Gary Hoffman wrote:
> Doyle,
>
> I've seen two, exactly opposite, views on this.
>
> One view says yes, run them. The heat from the filaments is supposed to
> activate the getter materials and absorb any stray gas. Thus preventing a
> failure.
The getter is active, its deposited on the inside of the glass. If there
are air molecules heating them with the filament causes some circulation
within the tube and eventually they wander by the getter. The warmth of
the filament will also drive adsorbed gas off the filament, grid(s), and
plate. But not nearly as rapidly as heating those elements up to glowing
also. Trouble is a bit too much gas can cause arcing or a gas discharge
that damages parts inside the tube at normal operating voltages. Running
a vintage tube with only filament or heater power has been recommended
by tube makers all my life, especially a good idea when applying decade
or two old surplus tubes.
>
> The opposite view - No, don't bother. The filaments are not hot enough to
> do any good.
>
> So.....take your choice. Its almost as bad as the arguments about VHF
> glitching in amps, with about equally divided views as to whether this
> actually exists at all.
I've seen plenty of VHF parasitic oscillations. Gets scary when the PA
under test is running 50 KW input at some parasitic oscillation
frequency. Not a time to run up to it real close with a grid dip meter
in wave meter mode! Or like my boss at Collins who had his nose against
the glass covering a PA compartment hoping to see where it flashed over
first and it flashed at the glass. That was just a 50 KW output final.
>
> 73 de Gary, AA2IZ
>
73, Jerry, K0CQ
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