Common items you passed up that turned rare when you wanted them

[Tony Duell]

> >The method generally used on TV tubes of the period (and I don't see why 
> >monitor tubes would be any different) was something like : 
> >
> >1) Over-run the heater. Typically a 6.3V heater would be run at 8V or 10V
> >
> >2) Apply a fairly high (200V-ish) +ve voltage the control grid (wrt the 
> >cathode), all other electrodes floating (no EHT applied either). 
> 
> Hi
>  I've had better luck with 0 volts. If the tube has not been used
> for a long time, it will be a little gassy. This tends to boil

Interesting... I've never seen this suggested anywhere, but most of the 
designs for boosters assume you'll be trying to improve a CRT that's been 
in use quite recently (e.g. a TV you've been watching), so presumably the 
gas problem is no so serious.

> off the cathode along with the other stuff. When you have the voltage,
> the electrons will hit the gass atoms and ionize them. These are
> then slammed back into the cathode. One article I read stated
> that the first stage should be done with 0 volts and then switch
> to a + volts on the grid(s)+anode for the last part.
>  I've not tried this myself but the method makes sense. In the
> first part, the getter has time to catch the outgassing. The
> last part helps to freshen the surface.
>  I know that there are many articles that state to put the voltage
> on from the beginning. I've also read in a only a couple of
> articles that the outgassing from the initial stages can poison
> the cathode enough to make the process useless. I recover
> many old vacuum tubes for my old battery radios. I've had
> good enough experience with the 0 volts and enough bad
> experience with the voltage on the grid/plate that I use
> the 0 volt.

Those valves are likely to be directly heated, right? I wonder if that 
would make a difference. AFAIK all TV and monitor CRTs are indirectly 
heated (well, I think there was a Japanese colour CRT that was directly 
heated, but I doubt you'll find one of those. Yes it did have 6 heater pins).

-tony