This supply provides 750 volts B+, and 375 volts B, using a typical voltage doubling circuit.  6.3-0-6.3 VAC is also provided.

A link to the Schematic is at the end of this page.  It’s made from junkbox parts, so use what you can find.   The components identified by ( ) in the description are identified on the drawing.

Transformer (T) and AC fuse (F1): An old tube TV 270-CT-270 VAC xfmr is used. The primary was probably sized for 115 VAC and it is estimated to be adequate for 300 ma. Present line voltage in the shop is 120 VAC as measured by digital volt meter of reasonable accuracy. F1 is a 3 or 4 amp AC line fuse.  It and a 3-wire cord provide basic protection.

Varistor (V): 20D-25; 20 ohm 4.8 amp steady working current. Provides some inrush protection since this supply uses solid state diodes rather than a rectifier tube, which the transformer was designed to work into. A tube rectifier is slow to produce DC when turned on, and thus provides some inrush protection.  Even with the varistor, there is still some inrush as indicated by the MA meter, so it is recommended to have the meter switch in the HV position at turn-on to refrain from bouncing the meter needle so much!
An alternative is to wire a 50uf electrolytic across the meter terminals, to slow the swing.  It will not materially affect accuracy.

Meter: This is a large Hewlett-Packard custom meter, with a 5 ma movement instead of the common 1 ma movement. The 56 K voltage multiplier (Rm) resistor is followed by a 50 K potentiometer (Ra) to allow setting the voltage reading accurately.  Adjust your design to accommodate the more common 1 ma meter.

Meter Scales:  On this particular meter, the 0-1 upper scale is used as a 0-1000 volt scale and the 0-300 lower scale is read directly as milliamperes.  Your meter will be different.

Meter Shunt (Rs): For measuring milliamps, a nichrome wire shunt (Rs) of approximately 1.4 ohms is used as the shunt, to accommodate the 5 ma meter. Note: Due to placing the ma meter in the negative lead of the diode bridge, its current flow will include about 6 ma through the two 68K equalizing resistors (Re).  This is compensated for by adjusting the meter shunt so that the meter reads 208 ma with a 2400 ohm load at 500 volts output (500/2400=.208).  Again, your meter and shunt will be different.

Diode Bridge (Br): The full-wave bridge rectifier consists of four CL04-12, 12 KV, 500 ma microwave diodes. We hope to never exceed the 500 ma draw but these are robust and tolerate overloads well.
The AC input to the bridge is via two red wires encased in black insulating sleeves.

HV Fuse (F2): An encased 750 ma microwave oven high voltage fuse (F2) is placed immediately after the output of the diode bridge rectifier and should blow should any significant overload occur in the filter capacitors, equalizing resistors or the load placed on the power supply by whatever it is connected to.
It is best to use an “encased” fuse so that if it blows, it won’t spray glass fragments around the inside of the device.
The idea here is to protect the hard-to-replace transformer.

B+ output is via a 10KV-rated test lead wire, feeding the RED terminal on the front panel.

B voltage (half B+) is taken from the junction of the transformer secondary center tap, connected to the junction of the two electrolytic filer caps. This configuration provides a voltage-doubler system to produce both the B+ and the B voltages. A blue wire feeds this half voltage to the GRAY terminal on the front panel.

Filter Capacitors (C): Two 100uf x 450 volt units are used, in series, for 50uf of B+ filtering. Each is paralleled by a 68K, 10 watt resistor (Re), which was what was in the junkbox. About 6 ma of current flows through this system (.006 x 750 volts = 4.5 watts of power flowing through these 10 watt resistors.

Safety Bleeder: A safety bleeder was not included, although good practice says one should be installed.  The equalizer resistors are so robust that failure is very unlikely (a.k.a. “do as I say, not as I do.”)

6.3-0-6.3 VAC for filaments feeds the GREEN terminals, providing either 6.3 or 12.6 volts.

Here’s a link to the hand-drawn schematic of the supply, as described above.

A Google Search for “W8JI power supplies” will produce a number of informative links.