[Boatanchors] SB-220 with parasitics

[w5jo at brightok.net]

Could someone explain this to me?  If a tube leaks, it will also have oxygen 
in the envelope with any other gas, wouldn't it?

If it has oxygen in it, wouldn't the filament go flash and burn into?

Over many years I have inserted NOS tubes in transmitters and, following the 
proper warm up period just applied power and never had a problem.  Just 
recently I replaced the 4-250 in my Globe King 500 with a glass bottom tube 
made in the 70s without a problem.  After 2 or 3 minutes of warm up I turned 
on the HV and it worked just fine.

Any tube will have just a minute amount of gas in it, that cannot be 
avoided, but that is the purpose of the getter to hold it during the 
manufacture of the tube.

In construction this is what takes place and I don' think very many hams can 
do it.


>From AI3V:   Quote
What is going on is the tantalum is heated hotter than red hot (orange or 
even white) while the tube is originally manufactured and connected to the 
vacuum pump.

During normal operation the anode is never allowed to get that hot, so it 
never outgasses any more.

This superheat or "bombardment " is a fundamental and critical part of 
creating a high vacuum.

The other problem with attempting to correct a bad vacuum by sammy hammy 
"gettering" is the tube, more or less cold will not work properly.

As you attempt to "getter" the rise in temperature will liberate more gas, 
and this gas will condense on any part of the tube that is cooler than the 
anode, you have both an electrical runaway condition, and no way possible to 
heat the glass red (or orange or white) hot to get the gas back into the 
anode.
Unquote



That is the best, short explanation that I have read and why I don't bother 
to worry.  If the tube has substantial gas it won't go away and you will 
have trouble.

Merry Christmas to all,

Jim
W5JO

-----Original Message----- 


  I half expected them to not
have full vacuum.