The Millen 90281 High Voltage Power Supply has a DC output of 700 volts at a maximum current of 250mA and a 6.3 VAC 4A filament voltage. Designed as a general purpose power supply it is an excellent power source for both the 90800 and 90801 transmitters HV and filament requirements.
The power supply uses two 816 mercury vapor rectifier tubes and has a two section pi filter with 10 henry General Electric chokes and a 2-2-10 mfd bank of 1000 volt General Electric Pyranol capacitors. All this power results in a one heavy power supply! When used to power my 90801 transmitter I also require another DC low voltage homebuilt supply to provide power for the oscillator/multiplier stage.
The first picture shows only the front control plate area as the remaining panel is blank rack panel. In the rear picture notice the size of the 10 henry chokes, on the upper left, in comparision to the 816 rectifiers.
Later versions of the 90281 had the capability of high/low voltage adjustment of the DC output. This is done through the switch located above the fuse holder and the terminal strip labeled LOW HIGH on the rear panel. Early version units do not have these items. The switch places a 5 ohm 25 watt resistor in the primary of the HV transformer for low voltage output. The jumper on the LOW HIGH terminal strip will either insert or remove the input filter capacitor from the circuit. Removing the input capacitor (LOW jumpered) changes the filtering configuration to a choke input type. Thus voltage regulation is improved, but output voltage is reduced. For early version units this same filter change is possible, but the unit must be opened and the input capacitance disconnected.
The Remote Switch terminals (both versions) allow the connection of remote switches which parallel the front panel filament and plate switches. The terminals can also function as a remote means for controlling an external antenna relay. The later is discussed in the article a Millen Station Setup Guide.
Owners: Don Buska, N9OO (Early Version), Tom Smith, N5AMA (Late Version)