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A Small Power Supply For Vacuum Tube Circuits

A small power supply for tube equipment.

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210 volt DC @ 75ma / 6.3VAC @ 2A

Here is a nice little project I built the other day. Before I get started, I want to state that this project should be built and operated only if you are experienced with making things that plug into the wall socket and that have other high voltages. If you reach inside this while it is plugged in, you have a good chance to land on your rump or worse.

Soon I will be building some more tube receivers and perhaps a small transmitter or two. For these projects I thought I would use one power supply for all of them. That cuts the cost of building down, and also isolates the power supply section from the rest of the radio.

This power supply is built on a 7x5x2 (17.75x12.7x5.1 cm) aluminum chassis. The chassis was made by Hammond in Canada. The chassis came with a helpful plastic film on the outside. I marked my measurements on this and avoided scratching the chassis. Sweet. I used some Greenlee chassis punches to make the larger holes and a Adel nibbling tool to cut the square hole for the power connector.

The transformer is a Hammond 269BX. Again a fine product from Canada. The power supply design is pretty much standard. The total output is rated at 75 ma, but the voltage regulator circuit uses 15 ma, so the main output is down to 60 ma. If you need a little more current, and don't need the 105 volt supply, the voltage regulator tube can be pulled.

The 10 ohm resistor on the output is not required but it is very handy for metering the current draw on that line. A voltmeter placed across the resistor will let you measure the current. 50 ma equals .5 volts on the meter.

The major concern of this project is safety. I used a recessed power connector (Cinch S-306-DB) so that contact while grabbing the male connector (Cinch P-306-CCT) would be impossible. Not that you should be pulling that plug while it is on anyway. The power supply is fused. A 150k 1 watt bleeder resistor is connected across the output. The wattage of the resistor is way above the required wattage. So it is unlikely that the bleeder resistor will open.

The 7.5k 4 watt resistor is actually a pair of 15k, 2 watt resistors in parallel. I hope to have a couple of receiver projects that use this power supply built and running in the near future. Good luck with your power supply. ~ Dave, N2DS

Dave Schmarder's Power Supply Back View Dave Schmarder's Power Supply Wiring View

Power supply schematic