Vacuum Tube

Why does it have to be a tube? What is it you are trying to do?

Depends on the vacuum tube. there are literally thousands of designs. And most are getting very very difficult to find these days, you can find audio amp tubes because guitar players still drink the vacuum tube kool-aid and refuse to use anything that doesn't use power hungry fragile glass vials in their amplifiers. vacuum tubes still find a very useful niche in very high power radio frequency power amplifiers and microwave transmitters because they have a faster slew rate than just about any solid state component capable of handling the same power. (solid state power dissipation goes up with slew rate quite quickly.)

Depends on thedevice that you specify/get.

I suspect that the technical challenge will be the distance for electrical isolation that you need for your voltage relative to the frequency that you have specified.

As an aside, I once saw a 3 phase mercury filled vacuum device. It was teh main rectifier for a coal mine and was rated some 300 plus amps at 1,100 volts. It was connected direct to mains. It had been decommissioned by the time that I saw it, but was located on a concrete pad in the middle of a paddock. Its enclosure was 2 shells of hand placed Lead bricks to stop the radiation and UV that it emitted while in operation.

It stood around 2' high and was around 3' diameter across the three poles.

Most vacuum tubes operate with plate voltages of at least 1-200 volts, and many higher power tubes operate at many thousands of volts. Most common vacuum tubes are voltage-controlled device - electron flow can be controlled by varying the voltage on the grid closest to the cathode (G1 or the control grid). In this regard, they behave more like MOSFET transistors than junction (PNP or NPN) transistors. Small receiving tubes were used in early digital computers (1940's and early 1950's) to fabricate various logical functions and to provide temporary storage and switching functions (via Eccles-Jordan flip flop circuits). Vacuum tubes are comparatively fast (compared to mechanical computers), and switching 100,000 times/minute would be no problem... in fact switching rates of 100,000 - 1 million times/second would be more like it.

Some vacuum tubes are still being made, but most low power vacuum tubes are only available from surplus stock or as pulls from obsolete equipment. Many collectors and hobbyists buy, sell, and trade vacuum tubes on eBay and Amazon.com, and some audio enthusiasts still prefer "vacuum tube sound" over solid state equipment. Another commercial source (of mostly high power or special function industrial tubes) include Richardson Electronics. Smaller/surplus sources can be found by simply Googling "vacuum tubes".

I should also add that they can give off X-rays, depending on the tube and the application so you should make sure they are shielded. (usually lead bricks aren't necessary)

I think that is only applicable for plate voltages in excess of 15 kV. Not many tubes live in that domain.

Except some specialty vacuum tubes like the Image Tube of a conventional Television set and some Old timer amplifiers the vacuum tube has had its best time long time ago.

There are many type of vacuum tubes. Diode, triode, pentode, hexode and to be straight forward: I am happy we have the transistor and different semiconductors as replacements and better performers.

Yes it can switch 100.000 per minute as switch but only in on-off.

The anode of a vacuum tube is almost always polarized as + (positive = see the name: ANODE)

Most vacuum tubes have a filament because the cathode needs heat to work. (Yes, there are exceptions) Their current is also more limited.

If you want to switch polarities you will need more than one in a stage (like Baxandall) or Push Pull just like transistors.

You will need to create a 0 (voltage threshold) between and refer to - or +. If you really want a AC voltage, you will need a stage with output transformer. and for switching that is not so interesting.

The type TRIODE has also 3 connections: cathode, grid, anode. But a faster switch will work better in a Pentode vacuum tube.

Unless you want to build stuff for museums I would advise you to use semiconductors. Vacuum tubes become priceless, unless you get it from dumps.

The old timers of us might have some left.

Bah! :-)

I can turn you onto sources for just about any tube you want. These are new tubes, most made in China, Russia, and eastern block countries. Some of these tubes are world class performers rivaling their ancestor counterparts.

If money is no object, there are sources for NOS tubes that will make your jaw drop when you see the price. However, stuff out of Russia, China, and the eastern block are priced cheaper than they cost in the 1960s when adjusting for inflation.

Well to be quite honest, I am referring to 17 years back. In Europe the originals became X3 to X 10 the price of the seventies. We probably relied on old stocks from originals. Good to know. Thanks for the hint. Dolf

Amusing, back when I was in school, folks used to ask how a transistor is like a vacuum tube. In a bipolar (PNP or NPN) transistor, a small current through the base-emitter circuit controls a large current through the emitter-collector circuit. The ratio is the gain of the transistor and is called beta or hfe. In a vacuum tube, the voltage between the grid and cathode controls the current in the cathode-anode circuit. The characteristics of a tube are more similar to an FET (field effect transistor) where the gate voltage controls the channel current. You should have no problem handling the voltage and frequency you specified. Tubes are used by some audiophiles who prefer the sound quality of a tube amplifier. You might find ads in magazines devoted to that interest. Most tubes these days, I believe, are made in Russia and Eastern Europe (and probably China).

Field Effect transistors are analagous to tubes. Both are voltage devices, whereas bipolr transistors are current devices.

Both fets, transistors and tubes can handle 200 volts or more, various currents and speeds and power levels at various frequencies.

High power and high frequency = TV transmitters of 500,000 watts = tubes are king.

Transistors have eliminated tubes in many lower power transmitters on AM and FM, up to 10,000 watts, and that power is being pushed higher each year.

Yes. I haven't looked at any electronics textbooks in years, but I would bet coverage of vacuum tube theory went by the wayside a long time ago. My first electronics textbook covered tubes first -- then solid state. Just shows the prevalence at the time.

I went through my electronics coursework in the late 80's and there was not a single mention of vacuum tubes.