Quote:
Originally Posted by jeyurkon
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.
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How about during cathode "breakdown" on the pumps, when the binder is baked out?... I have seen manifold pressure rise almost to 5 scale during that part of the process, and assume that near the cathode , the presssure would be much worse.
Quote:
Originally Posted by jeyurkon
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
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An odd part about my picture is the very shiny metal on the grid cup where a lead is attached... was the cup "cleaned" by the welding process?... or perhaps the lead acted as a heat sink and limited the temperature rise in that area, be it by processing or operation of the crt.
What is the melting point of silver solder, these parts usually become red during RF... 700-750 degrees or so, perhaps.
Just for grins, I rechecked the tube with my trusty old B&K 400. It was in the middle of the green "good" scale, after about a minute of warm up... no "hot shot" or "rejuvenate" was used.
jr