[Boatanchors] 4-1000A coloration ?

[Jim Wiley]

What you re seeing i mist likely due to electron bombardment of the 
glass, not unlike the way sunlight sometimes changes glass telegraph 
pole insulators to green or violet.   Is a sign of use, but not 
necessarily a problem, if the tubes were operated within their ratings 
and with sufficient cooling air. 


If operated conservatively, a 4-1000 or similar tube will last for 
several tens of years.  The biggest problem is excessive filament 
voltage, which can damage the emitting surface, and excessive drive, 
which can damage the grid.  Unfortunately, the only real way to test 
them is to install the tube in an operating amplifier and see how it 
does.  If it glows purple inside ( between the filament and plate), it 
is gassy, and probably should not be used.  Purple glow from the glass 
is OK - that glow is again due to electron bombardment


- Jim, KL7CC

.  

Paul Baldock wrote:
> I have just acquired three 4-1000A's. On each the inside of the glass 
> has a yellow discoloration in places, it looks a little like varnish. 
> Is this normal?
>
> Thanks
>
> - Paul
>
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