Required transformer voltage for voltage regulator tubes in series

Question

First of all some small context: I am attempting to design and build a clock with old electricial components, without silicon components. This question is about the power supply circuit. Note that I have no degree in electronics whatsoever, I have just been learning it as a hobby for a few weeks now.

For my circuit I will use a tube rectifier, e.g. the 6C4P rectifier. I will connect this, after smoothing, to voltage regulator tubes. I've picked the following, as I need the following DC voltage outputs:

• At least 450 V for dekatron anodes;
• Around 170 V for Nixie anodes;
• Negative 150 V for dekatron pulse (I can build this later on, but recommendations are welcome).

After doing some research, I am aware that one can connect voltage regulator tubes in series, to obtain different stable voltage outputs. I've picked the following voltage regulator tubes:

• 2x SG-16P (each around 85 V stabilised voltage, 150 V ignition voltage) = 170 V out
• 2x SG-1P (each around 150 V stabilised voltage, 175 V ignition voltage) = 300 V out

If connecting them in series and counting the output voltages, I should be able to get 170 V and 470 V if I am correct.

Now - if using the full-wave rectifier and a capacitor, what AC R.M.S. full load output voltage transformer should I pick? Do I need to count all the ignition voltages for the voltage regulator tubes as minimal DC input after the rectifier circuit? If so, I come up with the following calculation:

Voltage regulator tubes ignition voltages = (175 + 175 + 150 + 150) = 650 VDC needed after rectification and smoothing.

Currently I don't know the voltage drop of the rectifier tube and voltage regulator tubes, so I will just call them X and Y for now.

If 650 VDC after the rectifier/smoothing is correct, would this mean I need at least a full load AC R.M.S. voltage output of (650 + X + Y) / √2 on the transformer for max. efficiency?

Answer 1

The very first thing to do with vacuum tube circuits is to determine whether you need voltage regulation at all, and if you do, where you do.

Typical home radio receivers generally just used rectified line voltage (often without even transformer isolation -- those were fun times). Typical communications radios started using regulated voltages in the 1940's or '50's, but just for critical circuit elements like the oscillators that set the on-air performance.

Solid regulated supplies were known, but not often used. I'd start by looking at the tube specifications to see what the tolerances are on the supply voltages -- if the tubes can tolerate more supply variation than you get on the power line at your house, then just build a passive (transformer, rectifier, filter) supply. If you really need voltage regulation, then regulate just what needs it, not everything.

Having said all that, the simple way to make sure your regulator tubes will light up is to do as you say. I believe there are other schemes that would be lost to antiquity if it weren't for the ARRL and other amateur radio associations publishing handbooks every year since the 1920's or 1930's.

If I needed a regulated 450V and a regulated 170V in an all-tube circuit, I'd strongly consider getting the 170V with a shunt regulator (use regulator tubes in series as you're proposing), and use that 170V as the reference voltage for a series regulator. Again, old radio handbooks are your friend here -- there's circuits that use two or three triodes that will give you a regulated voltage from a reference -- think of them as 78-OH-MY-GOD-450 regulators.