I wish to experiment with valves (or tubes, if you prefer) and I shall begin by building a power supply. What voltages (at what currents) should it supply? Where may I find circuits? Naturally, the devices used should be easily obtainable.
Naturally? You best course of action is to move your birth-date back 100 years. Failing that, easily obtainable will be a stretch.
The voltage, current, will be determined by what it will power. Vacuum tube supplies, if variable generally had a variable transformer on the input to a line frequency power supply. These days you'd be designing and building a switching supply, so I guess the next thing you should ask yourself is if the power supply to be versatile enough for a wide range of applications (variable voltage) or for a single fixed purpose? And does it have to be authentic (use "valves" itself?)
To learn about tubes you may look for some vintage electronics company and start with a kit if you can find one, or find some old schematics and breadboard something.
In my practice year(1967) the first one was a device to show cosmic rays. It put 20.000 volts on two plates a 1/3 inch apart, less than 10 microseconds after a particle passed through those plates. The ionized trace the particle left behind showed as a flashing trail.
Next thing was an experiment control unit to print the count of five Philips counters onto one Kienzle printer in a radiation lab at predefined time intervals.
Both projects in tubes, working supply voltages 300 - 500 and 20.000 volts.
And I enjoyed them .
Worst accident was a set of four electrolytes exploding. (500 V reverse connected is a bit stupid........)
Then you might start with a big honking center-tapped high voltage
300-0-300 volt 1 amp transformer driven with a suitable variable transformer, and a separate well insulated step down transformer working at a fixed voltage of 5 volts 3 amps, driving a 5U4 vacuum tube rectifier.
The 5U4 is still in good supply, but all that stuff is going to cost you. And even back in the day the first thing to go was the vacuum rectifier replaced with a selenium or silicon diode rectifier.
But I think you'd be better off starting with an end project (or projects) so you know what the power supply should supply (V and I).
Then breadboard something vacuum tubish. There are plenty of schematics for the hobbyist in old magazines, old amateur radio books, and on line. Wood works well if it doesn't have to look good. Learn then spend more on chassis and chassis punches and metal working equipment.
I have never blown a tube. They are rather sturdy, and when an anode starts glowing, there is plenty of time to kill the power. However, I have blown a lot of AF118 transistors, when they could hardly deliver the power and cuirrent and slew rate demanded by a certain aplication...... Oh, and they were very expensive at the time.
Sure some niche applications. How many 1kV amps have you made in your life? (I've done zero. I guess I'd start with a 100V opamp and a 1:10 transformer, but then 'an opamp' is the hammer I hit all nails with. :^)
Hey I do have a ~200 Vp-p oscillator that runs a Rubidium lamp. (It's probably less that 200V once the lamp warms up and the coil get loaded down by the Rb vapor.)
There was a monstrous (~6 foot) klystron that pulsed the linear accelerator at the Vanderbilt FEL. High power/ voltage stuff is cool and scary.
Tubes can get you to places in voltage/current/capacitance space that no semiconductor can touch. Back in about 1990, I used an 813 transmitting tube to run the grid in an ion drift experiment, complete with a B battery. ;)
Haven't used one since, except in gizmos others designed.
I've always been amused by the thought of a bipolar current mirror _under_ the cathode of a tube (with grounded-grid)... I'll have to take some time and analyze that configuration... probably will need some kind of protective mechanism should the current mirror be "off". ...Jim Thompson
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