Tube vs. Solid State Preamp

one possibility would be a gallium field emitter, as used in focused ion beam milling machines--you make a needle with a dimple in the end, and the electric field pulls it into an atomically-sharp point. A very cool demonstration of electrostatics!

Cheers

Phil Hobbs

Oh yeah, those are neat!

Gallium ions would be even lower 'mobility' though (or since it's ballistic rather than resistive trajectory, should that be 'ballisticity'?).

What happens when it runs out, though? I've got 12AX7s that have conducted more than a few farads of charge. Eventually you get a cathode spattered with gallium (or amorphosized with gallium deposition competing with sputtered substrate). Just let it drip to the bottom like the old mercury toobs?

What's the vapor pressure of molten gallium, anyway? Lesse, 'Pedia says 1Pa at 1310K... probably not a big deal at 25C. Actual operating temperature could be high or low, depending on how you seal the thing... if you build it like an ordinary tube and dissipate real power, it could get quite hot. Or you could make it like a TO-247 with a small bell jar, keeping the cathode arbitrarily cold.

Tim

See...

(Gotta work on my lighting techniques :-(

...Jim Thompson

A coulomb is only 10**-5 mole, but yeah, gallium depletion is an issue. The nice thing is that you don't have to pump.

Cheers

Phil Hobbs

Thing is, you have to voltage-derate them big time even if the ripple is well within datasheet limits. "Yeah, you can go 130mph but only on Sundays, else the engine might seize"

I've seen a production guy whose shirt was ruined, the tantalum splatters etches their way through. If he hadn't worn glasses, oh boy ...

Dry-slug MnO2 tantalums are fine as long as you don't expose them to too much dV/dT, namely too much current. That means they aren't usually suited for bypassing power rails.

Derating 3:1 on voltage does seem to make them safe. Sometimes that's worth it. They have fairly stable ESRs over temperature, and work at

-20 or -40C when aluminums quit.

John

How old do you think I was when being shot at in North Africa with the Signal Corps? I did enlist at seventeen, but that was almost 70 years ago.

My brother's 15 months younger, and lives in Scottsdale. He owned the Ethan Allen furniture store in Phoenix and Mesa.

Wow! ...and I remember your 16th birthday.

I just looked at a grid-dip meter I built about fifty years ago. It used a 9002 triode and could oscillate up to 250 MHz. I think the selenium rectifier has gone west or it may just be the resistor line cord which dropped the line to heater voltage. Might be worth rebuilding!

Looks great. I assume this is with a digital camera. My last serious photography was with a 4 X 5 Speed Graphic.

This whole thing is worth a read:

"Another example is provided by the development of the 416A triode. The original and startling germ of a creative idea was that after all these years a triode might still be the best amplifier for microwaves, if only the spacing were close enough and the grid fine enough. An auxiliary idea was that close enough spacings could be attained and held by grinding the cathode and a surrounding ceramic co-planar, and then supporting the grid from the ceramic. These were, however, mere germs of an idea. Something real and complete was brought into existence only after years of concentrated effort, including the inauguration of a program of cathode studies which is still being pursued for other purposes."

I knew John Pierce at Bell Labs. When he needed a little more money for a vacation trip, he'd whip up a science fiction story for Amazing Stories, writing as J. J. Coupling.

Have we ever met? You name sure sounds familiar. What company halls have you "haunted" ?:-)

I did Motorola SPD, Philco Ford (Santa Clara), Dickson Electronics and GenRad (Phoenix), besides being independent for 37 years. ...Jim Thompson

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I remember a construction like that but it was not small. =20 Called a lighthouse tube, maybe 2" dia and 4" long.

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Guitar amps are very noisy. Just go to a local music store and have a listen. Maybe it is a scam of the amp manufacturers to have you buy their more expensive toob gear ;o)

Chris

The not so good ones usually hum. And badly engineered solid-state ones (meaning a lot of them) go *POCK* when someone turns on a GSM cell phone nearby. I am not a tube freak but I've never heard a tube amp do that, even if the design was a bit screwed up. Because it has no BE junctions.

But they _do_ rectify... just not as efficiently. ...Jim Thompson

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Very much less efficiently. I remember when I got my ham radio license as a kid. All the tube stuff in the neighborhood didn't flinch while pretty much all the transistor stuff fell off the rocker. My first debug job was an electronic organ, IIRC the Wersi brand. When I saw how they had "engineered" the thing I was almost ready to cry. It was EMI pandemonium. Plus the neighbor was a bit leery letting a kid like me with a $5 made-in-Italy solder iron have at it. But, we got it quiet. I depleted nearly my whole stash of salvaged 4700pF capacitors and use probably 10ft of solder.

Never bothered to measure; lack of proper equipment for starters - but seems to be a heck of a lot lower than common commercial tube stuff ("heck of a lot lower" naturally is a highly technical term).

It was line level; schematic gone - it was made over 45 years ago using midnite requisition military parts. One of the tricks was the filaments were run from a DC supply, another was all power was regulated in a different chassis (no AC to amplifier); the only commercial part was the Dyanaco output transformer made for a part-Williamnson, part cathode feedback circuit. Push pull parallel KT66 (i think), plate supply used a cascode regulator with regulation about 1v no load to 0.5A full load (??350V??).

I've seen quite a few tube PA amps that picked up CB radio, and police radios into the UHF Mobile band. Some small churches freaked out when a police call came through the speakers, at full volume during a church service.