eye-tube electron microscope

On a sunny day (Fri, 17 Nov 2017 03:11:04 -0800 (PST)) it happened Bill Beaty wrote in :

This is real:

EM84 was always a facinating thing to watch, in many old tube radios.

That was great! Thanks.

Oh boy a new set of youtube videos. Thanks Jan.

George H.

The spark plugs used as HV vacuum feedthroughs are brilliant. ;)

Cheers

Phil Hobbs

I only watched a little of the beginning. DIY science stuff is great.

George H.

sparkplugs!

Maybe one could reverse the polarity of a magnetic or electrostatic focus thing to defocus, namely magnify the cathode image.

Electrostatic lenses are pretty cool. Unfortunately Laplace's equation prevents you from making a negative ES lens because the potential has to reach its extreme values on a boundary, whereas to make a negative lens you need a potential maximum in the middle of the beam line.

That means that you can't make an electron optics system that has a flat focal plane. In practice you just adjust focus during a scan.

Cheers

Phil Hobbs

You physics guys are such spoil-sports.

How about over-focussing to enlarge the spot?

I remember our old round-tube RCA b+w TV, in a beautiful giant walnut case. When you turned it off, it made a big round spot for a while, with some features. Image of the cathode probably.

On a sunny day (Fri, 17 Nov 2017 16:09:47 -0500) it happened Phil Hobbs wrote in :

Indeed, what was fun to play with were 'vidicons', these are TV recording tubes, magnetic focus, a beam scanning a target at very low speed (as opposite to CRT where it is high speed) to remove charge build up by the projected image at the points where the beam lands. In fact, without light on the target, it images the target structure in extreme fine detail. Fun was playing with the magnetic focus, a large coil around the whole thing, with inside that coil horizontal and vertical defection coils. Changing the focus current would rotate the picture :-)

First camera I designed was a portable vidicon one with build in transmitter on nicad batteries... Way ahead of time, 1968, all transistor of course. Landed me a job a the TV station.