12LP4 post mortem

[jeyurkon]

Originally Posted by jr_tech

Bill...

I have posted a picture of the gun in a 10FP4 that is in a GE 10T4 set that I am working on. The Grid cup and G2 show plenty of yellow to blue color... does your gun resemble this? This tube is not gassy and is a strong performer.

I have always thought that the colors that I see here were developed during pumping due to the RF heating of the gun before it was sealed off. I believe that in those days, gun parts were NOT hydrogen fired before processing. But this is only a guess.

jr

jr_tech, the vacuum would haft to have been very bad for the electrodes to end up looking like that after induction heating. It wouldn't explain the graduation in color that we see either.

I've done a lot of evaporations using boats made of various metals in vacuums as bad as 10**-5 Torr and have never noticed anything like this.

Maybe when they activate the cathode and convert the carbonates to oxides the excess oxygen that is released isn't pumped away quickly enough. It would require a lot of material to do that though.

But now that I see your photo I think my explanation was wrong. It certainly still looks like oxidation, but did they silver solder the leads to the gun assembly rather than spot weld them? Doing that in air would account for the coloration.

What do you think?

John