Valve Power Supply


This power supply will be used with the valve transverter elsewhere on this site and a number of other planned power amplifiers as only one will be active at any one time. However, the heater and bias supplies are sufficient to enable all of the units to be run continuously on standby for instant switching in contests etc. The unit, which fits into an SB-101 case and is painted to match my other Heath equipment, will provide 12V/12.6VAC at 12A, 6.3VAC at 4A, 6.3V AC at 4A for heaters, -150V at 30mA for bias, 300V / 420V DC at 200mA for general HT supplies and 1300V DC at 350mA for the PA supplies - only one PA in actual use at any one time although all may be on standby. The completed unit weighs 44 pounds.

This photo shows how it all started with the chassis, front and rear panels and side cheeks after initial assembly and before drilling the component mounting holes. All of the flat pieces are made from NS4 half hard aluminium which is extremely strong but too hard to bend. The side cheeks are made from a softer grade of aluminium which may be bent. Tapped ‘U’ shaped support  sections of 0.5 x 0.5 x 0.125 inch aluminium are used under the chassis to hold the front and rear panels in place, take the mounting screws that retain the assembly within the case and the case feet in place and for bracing.

The first photo shows the completed and boxed unit from the front with no power applied. Each main supply block has a separate mains fuse and front panel indicators, neons for high voltage AC and DC and lamps for the low voltages. The meter allows each DC supply voltage and current values to be monitored.

This photo shows the rear panel with labelling for the various power and loudspeaker connectors. Each output connector has 12 ways and all of the heater supplies are completely isolated from the chassis and wired separately to each outlet to minimise the risk of hum loops.

This photo shows the internal layout and wiring. The large transformer on the left is part of a self contained assembly with its own PC board holding rectifiers, smoothing and bias detection lockout circuitry which supplies +420V, +300V, -150V and two 6.3V supplies. The transformer on the right has another PCB containing the 1300V supply and smoothing. Two additional transformers provide the bias supply and 12/12.6V at 12A. All cabling is held in place with P clips which make maintenance rather easier compared to a laced cableform.

The block diagram to the right shows the various supplies and their respective modules. Each rear panel outlet has a 230V AC supply for cooling fans and unusual supply voltages that are impractical to include in the main power supply unit. Most but not all of the external units use the 12/12.6V heater supplies. The 23cms PA will use the two 6.3V supplies which will remain isolated from ground.