I like these new "Energy Saving Vacuum Tubes". They've replaced the old power wasting filaments with orange LEDs. The tubes look identical. Better yet, you can connect a potentiometer to control the brightness of these LED "Filaments".
These tubes run cool. No more burnt fingers when removing them from the socket, while they are operating.
Get a bunch, build a circuit with them, let us know how that works out for you.
And yes, I want some curve charts for the final results.
Jamie
So, how's the cathode emission?
-- www.wescottdesign.com
-- Got a link to these wonders?
He just got sucked in by the Greenies doing what they do best.
is just the smart people making what people want to buy, make a standard solidstate amplifier, add a few tubes from the scrap bin on top shine an orange led though the bottom so it looks like they are doing something
-Lasse
They canot be the same, period. the only solid state device that can emulat e a triode is a JFET and they do not go that high in voltage. Depletion mod e MOSFETs are NOT the same in that they inverse conduct. oyu might bwt them to act close with a high speed diode in series with the drain, but will it be the same ? I doubt it.
They finally did make solid state replacements for tubes. Most common were rectifiers. Then someone did make some dorpin replacements that were largel y used in VTVMs.
The audio people will never accept this, however I did see a tube preamp wh ere they put lights under the tubes to make them glow green or something. H owever these were still the old ECC83s or whatever and were actual tubes.
I want to see them emulate a pentode though, that might be fun to watch. As far as I know, so far only diodes and triodes have been succcesfully emula ted. There have been dual gate FETs used in synchronous demodulators that s ort of emulate a pentagrid or at least aa tetrode, from its application. bu t it is nowhere near a dropin, not at all.
Bottom line IMO, if you want tubbes, use tubes. If you got a regular class AB solid state amp leave it on all the time, but if you got tubes you have to shut it down when not in use unless you want to heat your house.
Problem is that you are burning cathodes doing it.
I've got tubes somewhere that glow blue-green. They're VFDs, effectively direct heated triodes.
NT
I think this is in reference to LED lamps that look like filament light bulbs. The 'filament' is a PCB with a series of blue emitters, with a light-pipe coating and phosphors. Depending on the phosphors, you can get any color (even white). As a method to get 4pi steradians of light from a bunch of 2pi-steradian LEDs, it's effective. Also, attractive. The weakness is in cooling (decorative lights, yes: bright illuminators, maybe not).
They canot be the same, period. the only solid state device that can emulate a triode is a JFET and they do not go that high in voltage. Depletion mode MOSFETs are NOT the same in that they inverse conduct. oyu might bwt them to act close with a high speed diode in series with the drain, but will it be the same ? I doubt it.
Specifically, the physics just don't match up (obviously..?). To make a FET's "plate curve" look like a pentode, you need quite a high pinchoff or threshold voltage, but that is impossible while keeping the transfer curve too.
A sufficiently small (semiconducting) diode in series would do fine to replace the cathode; getting rid of recovery isn't so much the problem as getting low enough capacitance to keep circuit impedances high. It's probably possible to dimension such a thing to achieve better high frequency performance than common applications (e.g., 5U4, 6CL3), if not others simultaneously (6AL5 claims 50mA peak, 330V PRV, and a ~500MHz SRF, and doesn't have to worry about drift or recovery anywhere near that region; indeed it performs better than most Ge point contact diodes).
glow green or something. However these were still the old ECC83s or whatever and were actual tubes.
Sadly, from one of the great names in audio, McIntosh themselves!
I want to see them emulate a pentode though, that might be fun to watch. As far as I know, so far only diodes and triodes have been succcesfully emulated. There have been dual gate FETs used in synchronous demodulators that sort of emulate a pentagrid or at least aa tetrode, from its application. but it is nowhere near a dropin, not at all.
It's one thing to approximate the plate curves of a multigrid tube, or the transfer curve (including for multiple grids at once). It's quite another to do so when one must include electrode currents for those grids as well -- grid current for transmitter types, screen current for anything using one, etc.
One of these days, I feel I'm going to leapfrog everyone who's ever made a tube model, including Reynolds and Leach themselves. The physics isn't too bad, it's just different.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Take a look at the Fetrons
Isn't there some program that lets you trace the tube curves in a Java applet or something, that then dumps a SPICE model to a file for you? I wish I could find it, I'd like to be able to use a SPICE model for some of these Soviet submini triodes/pentodes I bought on eBay.
There seems to be no reason that a (working) vacuum tube cannot be made without a filament. A properly biased semiconductor emitter would appear to be the answer.
Photocells and photomultipliers are vacuum tubes, and haven't any filaments.
Semiconductors have LOW work functions, but not zero. You need photons, or very high local fields, or heat, to get any significant current. This comes from the quantum mechanics of transitioning from an electron-in-a-solid to electron-in-a-vacuum which has very low probability/rate/matrix element. That rate is a lot better in PN junctions, because P-doped and N-doped material have nearly the same bands.
Physics is cool!
Vacuum tubes are basically BJTs or FETs without charge balance and bulk resistance (resistance in the physical sense) in the active region. The cathode and anode work the same; there is an emitter and a collector, and thermal energy is required to exceed the work function.
Here's a 6AL5's exponential region:
There's a depletion region, too, though it's not nearly as important (you can't get very many electrons into an unbalanced space charge). Its effect can be felt as a loss component that goes as f^2, which becomes important in the 100MHz range for most types.
Basically the reason semiconductors are so many orders of magnitude better is, almost one order comes from the energy threshold (a bandgap of 1.1eV means electrons are free to move around *inside* the material; a work potential of 10eV means they're free to move around *outside* the material as well!), and the rest from charge balance and miniaturization. Charge balance carries the downside of resistance and diffusive transport, but because the devices are so much smaller, it's by far a net win.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
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