kodera2tNowadays constant voltage is easily obtained by Zener diode or three terminal voltage regulator but in the vacuum tube era, voltage regulator tube was widely utilized. It can generate high (more than 75V) constant voltage and it was quite useful for oscillator stabilization or some high precision amplifier. (Actually I have no idea how to generate constant 150V DC, even now ;-) Several kinds of voltage regulator tube was fabricated and this time I got 75V version, named VR75. The following video shows how it works. It is quite simple but useful tube!
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Those VR tubes have a gas mixture (usually neon) in them which has a precise firing voltage.
That reminds me I once made a darkroom enlarger timer (turned on lamp for a certain number of seconds) using a triode, a neon lamp, and a relay. The relay was from discarded phone switching equipment and used about 30-50V. A momentary switch connected the HV supply to a current limiting resistor and the relay. A very old octal base triode (also from discarded equipment) was wired in parallel with the relay. This was normally biased off with a resistor to a negative supply. A RC circuit with a potentiometer for the R charged the C, and a neon lamp, which had a precise turn on voltage was connected between this and the grid. When the C voltage became high enough, the neon lamp fired which turned on the triode, which "shorted out" the relay, turning it off. A pair of contacts of the relay were wired in parallel with the momentary switch to latch it for the duration of the exposure.
Ah those were the days. Thought nothing of working with HV.
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Very interesting ancient "blinky" !!
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Hahaha yes, an adjustable "blinky" for darkroom work.
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To generate a constant 150V the principle is the same whether tube or transistor, have a feedback amplifier sample the output voltage through a resistor divider and compare it with the reference. If you had a 75V reference, then you would compare it with half of the output voltage, and use the difference signal to control the valve in series with the load.
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Ha ha, yeah it will be like that. Lower constant voltage standard (for example, exact 5V) will be enough to get stable 150 V, if resistor divider is reliable..
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And of course any variation in the reference voltage will be magnified by the step down factor.
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