Mosfet One Channel Schematic
The EHHA Rev A Mosfet version schematic.
BJT One Channel Schematic
The EHHA Rev A BJT version schematic.
Rail Power Supply
The on board rail supply is a very conventional split supply using adjustable linear regulators.
EHHA Rev A Split Rail Supply
The EHHA Rev A board provides two heater supplies depending on whether you are using a 6.3-7V transformer or a 9V transformer. With the stock components the supply is adjust in approximately a 1V range around 6.3VDC.
Use 1N5822 Schottky rectifiers for this power supply.
Heater Supply for 6.3V Transformer
Use UF4004 rectifiers for this power supply.
Heater Supply for 9V Transformer