boiling off electrons

There certainly are holes between the grid wires. How else can electrons sneak past when the grid is, say, -20 volts? If the grid array were a perfect Farady shield, no electrons could get through.

The positive plate potential sort of reaches between the grid wires and projects fingers of positive potential towards the cathode, allowing electrons to be sucked through.

If you move the grid wires closer together, a negative grid bias would be more effective in reducing plate current; the cathode would essentially see a better far-field Farady shield. Variable-mu tubes had a nonuniform grid spacing so that the transfer characteristic had a long tail... the close-spaced part of the grid cut off at a lower negative voltage than the wide-spaced part. Wider holes.

Yes, you'd have to do a proper field analysis to see what's going on in a more precise way.

John

When I was in USAF electronics tech school, somebody would always send some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer amplifier (when you're buffing the floor).)

Cheers! Rich

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry Dept. instrument repair shop, the standard thing was to "tygonize" them. What you'd do is get a nice length of tygon tubing and a large cigar. Then when one day when the unsuspecting newbie has some hyper- expensive piece of gear on his bench he's fixing, you surreptitiously snake the tubing into the instrument and when the newbie thinks he's got it fixed and flips the power on, from around the corner you light the cigar and blow smoke into the machine which then pours out of it like it's on fire! Much fun then ensues as newbie panics! :-) Yeah, they got me that way too.

I would have dropped the asshole with a bench stool before he could get away from my bench. OTOH, my bench was usually out in the open, away from any wall, and had space to walk all the way around it so your childish stunt would be quite obvious. I had three benches at my last job, along with a lot of equipment cats and a 4' * 8' table for schematics. I was working on 80,000 telemetry receivers. The only way to pull your stunt would be to drill a hole in the bench, and try to hide the hose.

I'll keep that in mind if I ever hire you.

(note to self: use hollow floor) (note to self: stay out of stool range)

:-)

Concrete slab. ;)

And those old die cast HP equipment cases! The handles make them easy to hold on to while you wind up for the 8660 toss! ;-)

We had a jerk there that walked around hitting people in the back when they were concentrating on the item they were testing or troubleshooting. He did it to an old man working on the only high voltage product in out line, and almost knocked him off his bench stool. I waited till he was talking to the test department supervisor and told him if he ever did that to me, or to Jerry again I was going to knock him on his ass. He puffed up like a blowfish and informed both of us that he was 100 pounds heavier than me. I pointed to one of our new, OSHA approved 75 pound padded bench stools and told him it would probably take the top of his head off, and to leave people alone. He snarled at our boss and said, That SOB has a big problem. Our boss grinned and said, It sounds like he gave you some good advice! He was just about the only tech there who wasn't a Veteran, and had no idea what would happen when he went too far. He was too stupid to understand what he was doing was considered assult. He complained to another Veteran on the test floor who informed him that old soldiers can still kill, when they are provoked long enough. He finally realized he could end up dead if he didn't stop.

I forgot to mention that at times I have severe allergies to tobacco smoke. I had one moron light up and blow smoke in my face one day, knowing how it affected me. He was laughing his ass off. The next morning, he did his usual of switching on the central AC and lighting up in front of the intake. He took one puff and ran to throw up. I had used an entire can of Lysol just before he walked in, so when he took his deep puff, he nearly passed out. Problem solved, and no blood was shed that day. :)