"High" Voltage Mosfet Amp

Lower temperatures produce far too few electrons (as you already know very well, the electrons are produced both from thermal emission _and_ field effect), lessens the beam intensity, and reduces the rate at which work can get done (beam sweeping rate.) Which impacts productivity. By quite a lot with even small changes. Higher temperatures works great for beam intensity, but quickly destroys the emitter. (Which is also treated with Lanthanum hexaboride, memory serving.) The trick is to accurately temperature over time without drift. And we are talking on the order of tenths of a Kelvin to perhaps one Kelvin, where possible. Now think about the local (dI/I)/(dT/T) problem at those temperatures T, if done pyrometrically, even assuming emissivity doesn't change over time.

Early solutions were to use inordinately expensive current drive power supplies (better than 0.1%.) They may drift a little and need recalibration but that's less important because the tips themselves age faster still. But the reality is that the temperature at the tip is the thing to be controlled, not the current driving it. The tip temperature needs to be closed up within the control loop. Periodic adjustment using disappearing filament methods and calibrated (expensive) tungsten standards achieves bringing temperature into the loop, if done manually and frequently. The problem is... well, all the problem in doing that. It means other specialized power supplies for the standard lamp, careful logging of lamp usage and recalibration as needed, regular procedures done frequently, etc.

Variations in lifetime might be as much as a factor of 50X for the exact same system, depending on customer procedures. And at the high expense of replacement, it becomes urgent to find an easier way to achieve more uniform experiences.

Jon

...

You are talking about lanthanum hexaboride emitters. IIRR the ones we used had a single crystal of LaB6 mounted on a U-shaped chunk of wire, which served as the heater. This design seems to have been superseded

This had the interesting property of producing a rather narrrow cone of electron emission, which meant that we had to put double deflection coils at the gun to get the most intense part of the electron emission lined up on the axis of the electron microscope column; we had to rotate the beam as well as getting it across to the microscope axis, whence the need for a second pair of deflection coils.

Much better than the tungsten sources it replaced. I once got to thank Alex Broers - at a dinner party in Cambridge - for inventing the LaB6 electron source (many years earlier when he was at IBM)

Particulary when its the temperature of the tip of the LaB6 crystal that matters, rather than that of the supporting wire/structure.

That I can imagine. In principle the spectrum of the optical emission

- which is to say the relative intensity at at least two different wavelengths - from the tip of the LaB6 crystal should give you enough information about its temperature to run a control loop. but the devil is always in the details.

-- Bill Sloman, Nijmegen

"Bill Sloman is so Full of Bullshit "

The Quad ESL63 had rather more than a transformer to drive the electrostatic moving parts

Got nothing to do with you mad assertions re the ESL57.

FYI:

The impedance presented to an amplifier by the ESL57 is at or above 8 ohms from 25Hz to 7kHz - which easily covers the entire power band in recorded music.

From 50 Hz to 5 kHz, the impedance is 15 ohms or higher.

Any hi-fi audio amp (valve or SS) worth the title can drive such a load with recorded music signals.

You have no case.

Fuck off.

..... Phil

It was sputtered material on tungsten, not a crystal. It's possible I remember wrong about the material, though.

Jon

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corded

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A simple transformer is going to look like a capacitor at a sufficiently high frequency, and many hi-fi amplifiers of the period were sufficiently badly designed that they would oscillate when presented with a capacitative load, to the extent that it wasn normal to add a "Zobel network" to the output to make sure that the load - as seen by the amplifying elements - stayed resistive up to a few MHz.

Why don't you f*ck off, rather than boring us with your half-baked pseudo-expertise embedded in the usual unoriginal personal abuse.

-- Bill Sloman, Nijmegen

"Bill Slowman is Totally Full of Bullshit "

The Quad ESL63 had rather more than a transformer to drive the electrostatic moving parts

Got nothing to do with you mad assertions re the ESL57.

FYI:

The impedance presented to an amplifier by the ESL57 is at or above 8 ohms from 25Hz to 7kHz - which easily covers the entire power band in recorded music.

From 50 Hz to 5 kHz, the impedance is 15 ohms or higher.

Any hi-fi audio amp (valve or SS) worth the title can drive such a load with recorded music signals.

You have NO case WHATEVER.

Fuck off HELL and DIE !!!

you VILE pile of demented, autistic SHIT

..... Phil