Lighthouse Electric Power Supply Project
Some Application Examples:
Some Application Examples:
The power supply reassembles two small low-voltage transformers, a couple of fuses, capacitors, resistors and four rectifier diodes or one rectifier bridge. The transformers are connected back to back, the 12.6 VAC output of the first transformer is connected to the 12.6 VAC CT output (2 x 6.3VAC) of the second transformer. The secondary winding of TR2 develops about 230 VAC. A full wave rectifier connected to it produces about +250 VDC under load. The first transformer TR1, in addition to powering the TR2, supplies two different filament voltages. 12.6 and/or 6.3 VAC are available. To protect both transformers from short or overload, line input and HT output are fused as indicated on the schematic. The 220k resistor at the output, discharges the capacitors in case there is no load connected to the output. However, do not operate this power supply with no load as the voltage on the filter capacitors may rise to 300 VDC or more. For testing purpose, a 10 kOhm 5 Watt load resistor may be used for short periods of time.
Potentially lethal voltages can be present. Do not touch any part of the device with bare hands while under power. After disconnecting power, wait until filter capacitors are discharged. Measure voltage with voltmeter to be sure. If you do not know how to handle high voltage circuits, do not build this device. Get help from a qualified technician.
Our prototype was built on a metal box (chassis). The two transformers were bolted on top. Underneath, two strip terminals were mounted. On the front, five holes were drilled to accomodate a power switch and four binding posts. Two posts were designated for HT B+ and common ground, the other two for filament output. A power-on indicator can also be added. The back had three holes. Two holes for the fuse holders and one hole for the power-cord. All components were soldered to the solder terminals. In that type of assembly, axial or radial capacitors can be used. Make sure the polarity of the diodes and capacitors is correct. Double-check your wiring before applying power for the first time. Do not install the HT B+ fuse at first. Switch your voltmeter to 500 Volt AC. Apply power and measure transfomer output voltages. TR1 should have about 12 to 13 VAC and TR2 should have about 230 VAC. If the voltages are present, turn off power and install the HT 50mA fuse. Switch your voltmeter to 500 Volt DC and plug into the HT binding posts. Connect a 10k 5W load resistor to the same posts. Now turn on the power. The voltmeter should indicate about 250 Volts DC instantly. If not, turn off the power immidiately. There is a wiring error. Correct the problem and try again. HT fuse may be blown. If you do not have a load resistor available, do not apply power for longer than 2 seconds.
TR1 = Step-Down transformer 115 VAC-12.6 VAC CT 2-3 Amps (Jameco PN:29225CL)
TR2 = Step-Down transformer 115/230 VAC-12.6 VAC CT 2 Amps (Jameco PN:102154CL)
BR1 = Four diodes 1N4007 (Jameco PN:177674) or Rect. Bridge (Jameco PN:178087)
C1,C2 = 22uF/350V Radial Electrolythic Capacitor
R1 = 1k Ohm 2 W
R2 = 220 kOhm 0.5W (or 2x100kOm 0.25W parallel)
F1 = Fuse Holder and 0.25A AGC fuse
F2 = Fuse Holder and 0.05A AGC fuse
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