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RE: Is this feasible? Rectifying 6.3v for heaters




Hi Pete,

Here is the schematic of my updated B+ supply in my HK Citation 4.

The rectifier is now a full wave silicon bridge which feeds the pass transistor which is an N-channel power MOSFET. The heart of the regulator is the TI TL431 shunt regulator which contains the reference. The regulator is coupled to the pass transistor via an optocoupler (4N27). The regulator chip and optocoupler are powered from the heater supply.

The filter network of the OEM PS is retained and voltage from the new regulated power supply is adjusted to match the value on the schematic of the OEM supply. With a regulated supply the OEM filter is over kill but I wanted to preserve the essence of the Citation 4.

This regulated power supply is not from some frivolous desire to do it because I could. This preamp fed my Citation 5 for my main speakers but also my subwoofer (Electro Voice 30W) via a MOSFET amp which I built. Every time the fridge came on or off my subwoofer system went nuts. The regulator solved the fridge / subwoofer issue.

The remaining mod is that the ON/OFF button is now illuminated by an embedded green LED. When I was using the grunt three terminal regulator for the heater supply I lit the LED in a manner similar to the OEM by putting it and it's ballasting resistor across the regulator. That worked but the LED would vary in brightness greatly with line voltage. I was not going to have that so it now is powered from the heater winding of the power transformer ballasted with capacitors and full wave rectified. I will add that to the heater supply schemo and scan the updated version.

Phil

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