ON-CHIP VACUUM MICROTRIODE

Oh no. Not again.

This is device-specific, but generally very true.

The reason that this seems to contradict the 12AX7 above is because Child's law applies to parallel infinitely large surfaces, among many other assumptions. Real devices have their own (different) exponents. The ideal 12AX7 has an exponent very near 1.0.

Thanks, as always,

Chris Hornbeck

It's the electric field drawn between the plate and grid. Namely, that which leaks through the grid wires. It's like putting a resistor divider between plate, grid and cathode, but because it's electric, it doesn't cost any current. Slick, eh?

Tighter grid spacings have higher Rp and mu as a result.

Actually, it won't: the curve of mu vs. Ip varies a bit more than 6SL7, according to GE's datasheet. It's still pretty good though.

Obviously, it succeeds better at higher drive demands; a 6SL7 won't very well drive a 22kohm load.

Tim

-- Deep Fryer: A very philosophical monk. Website @

A JFET would be a starting point.. A MOSFET for a pentode..

jFET looks like a pentode too.

I'm not aware of any solid state device that has a triode transfer characteristic.

You're quite welcome.

Those supertex jobs are the only readily available high voltage depletion mode FETs, of any type, I've been able to find and I keep thinking I'll try them too one of these days but a plain ole MOSFET works just fine for DC coupled concertinas and followers, the two places I sometimes use them, and for the guitar amp front end I opted for the known low noise characteristics of the jFET with an NPN cascode.

Any memory device with table lookup will work just fine.

I did mean 'a' device, not a 'circuit'.

You do realize, of course, that digital can only approximate analog.

Dirk Bruere at NeoPax snipped-for-privacy@gmail.com posted to sci.electronics.design:

Maybe, maybe not. It might be the key to terahertz operations or possibly deep UV lasers (petahertz).

Huge NONLINEAR input capacitance.

I believe you can say good bye to Hi-Fi without using a deep feedback. And if you are prepared to use feedback, be aware of the stability issues due to the said capacitance.

However, TO-220 version of such a MOSFET (with a denerative source resistor) can be a funny replacement for EL84!

Regards, Alex

e%3Awww.Supertex.com%22

There is no SS device like a triode which gives the typical highly sloped curves for Ra at different Eg values. The Ra slope indicates dynamic plate resistance which is always lower than the load value to be driven.

All ss devices have collector or drain resistance curves like pentodes. The Rc or Rd is usually always a higher resistance than the load connected.

The curves cannot be changed to being like triodes unless you have lots of series or shunt voltage NFB applied.

Local series current FB in a typical mosfet ot j-fet or bjt set up for gain does not reduce the drain or collector output resistance, but increases it, so the drain or collector curves become even more horizontal although spaced more linearly for various bias values. So local current NFB raises Rd, Rc, and tube Ra.

When wanting a triode, don't phucabout looking for a chiperized version. be a man and go for a tube socket and bottle!!!

Patrick Turner.

flipper wrote: ...

And vice versa.

Sheit, yes. Back in the oldfartdays(.com), MosFets were at best

'F' and I looked into the newer MosFets becoming KT-88s.

..and I don't mean FMIC... He got my PH#...

Can be done, and done cheap. Got the data.

JJTj

"ooh Gooddy !! Send me to the Twilight Zone again..."

SEND ME ! !!!!!!!

(Cheryl 'Devil Girl' Borck)

triodes.

Technologies)

rotated

You also do realize, of course, that analog can only approximate analog. At least with digital, copying is bit perfect after the first conversion.

Maybe you missed it but I said the two places I used them were follower and concertina. Both of those are essentially 100% local degenerative feedback and, as such, there is no input capacitance or stability problem.

IMO that would be a wasted effort because you'd lose the soft clip characteristic of the tube.

Seeing as how digital circuits can be and are made from analog devices that would be a resounding 'no'. You simply throw away the vast majority of available information content in exchange for noise immunity and, voile. Nothing 'approximate' about it. Or, if you prefer to look at it from the converse, digital is, by operating principle, 'approximate' and, assuming binary, anything 'around' 1 is deemed 1 while anything 'around' 0 is deemed 0, give or take an indeterminate jiggle of thresholds, approximately.

As an amusing coincidence, a few days ago I just happened to have built a multi-vibrator with a 12AU7 operating entirely on 9 volts. I was curious to see if 'something' could be done with a tube and 9V battery and while it wasn't the best MV ever made it was digital, alright. Oh, and it worked.

However, I wasn't proposing to substitute an analog device for digital, as you were in reverse, so it's moot.

(snip)

But a purely digital device would, at no time, produces a value that is not either a one or a zero (zero transition time between logic states). And it would have no propagation delay from input to output. Analog devices only approximate ideal digital devices.

No, no, these were integrated vacuum tubes. It was two plates (flat pieces), ceramic I think, with patterns deposited on them, spaced closely with a vacuum in between. A cathode circle was surrounded by a grid ring, and the anode was on the facing surface. You could have hundreds of these, with resistors and capacitors also deposited on the ceramic plates, in one compact assembly. The cathode material was chosen to emit electrons with moderate heating, and the metals used for grid and anode were chosen to not emit (nearly as much, anyway). It could obviously be designed to withstand heat that would kill common silicon semiconductors. However, the mu of the tubes was quite low with that geometry.

Cheers, Tom

There is no 'ideal' anything and using your criteria a digital device is, itself, an 'approximation' to a digital device, rendering the distinction meaningless.

Even so your argument of theoretical 'ideal' devices still does not hold because an 'ideal' analog device would also have zero propagation delay, infinite frequency response, zero noise, and perfect linearity. And, as such, it is a trivial matter to wire it so that, again assuming binary, any 'ideal' digital input instantly results in a 'hi' or 'low' with no intermediate states. I.E. an 'ideal' digital response, no 'approximation' involved.

And since digital circuits *are* made from analog devices your continued insistence on arguing against the plainly obvious is like stubbornly arguing that dogs don't bark while standing in a kennel full of barking dogs.

Have it your way. But don't be too surprised if no one asks you to help design any state of the art digital electronics, where transmission line delay and ringing from less than perfect termination impedance match, signal time skew (variation in propagation delay) and other analog effects set the limit on how much performance you can get out of a given digital technology. Those are the dogs I hear barking that you seem to have no awareness of.

-- Regards,

John Popelish