Lighthouse Electric Tech Support

 

VTPS4 - Converting AC Filament Supply to DC

VTPS4 PSU, can be easy converted to DC filament supply implementing a full wave rectifier and an CRC filter, with one pole grounded, as shown below.


Fig. 1

Fig.1 shows a 12.6 VDC circuit, as used on our STA1 pre-amp. This amplifier draws only 0.5A filament current. Therefore, a 50V/2A rectifier bridge and 1000uF/25V filter capacitors for C1, C2 are sufficient.
The series resistor value should be determined for 12.6 V output under load (tubes connected).

Vacuum tubes are very sensitive in regard of filament voltage and should be operated at as near the rated voltage as possible.
Useful tube life can vary significantly with only a 5% change in filament voltage.

Most common value for the series resistor in this circuit is 2-3 Ohms. Choose a wire wound resistor with minimum 5W rating.
Fig.2 shows a 6.3 VDC filament circuit.


Fig. 2
The components for this circuit should be calculated according to the load current. Over-rating the values for the rectifier diodes and capacitors is not significant.

You can further reduce the output-voltage ripple by minimizing the current ripple that the output capacitor is forced to absorb, so the use of multiple small caps instead of a single large component can be beneficial.
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THESE PROJECTS ARE PROVIDED 'AS-IS', WITH NO WARRANTY OF ANY KIND.
USE OF THESE CIRCUITS SHALL BE ENTIRELY AT THE USER'S OWN RISK.

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