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RF_PREAMP_SUPPLY

2015-03-22 03:31  
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RF_PREAMP_SUPPLY
Early tube-type receivers used filament voltages of 6.3 and 12.6 Vac, but had no low-voltage dc power supplies. The figures show how to borrow a little of the filament voltage, which is rectified and regulated to provide 12 Vdc for the preamp. In the 6.3-Vac version, diodes D2 and D3 act as a simple voltage doubler to step the input voltage up to approximately 15 Vdc. While the 220-μF capacitors used for the voltage doubler are sufficient for the load presented by the preamp, they will not provide the 115 V dc to the input of the regulator at more than about a 25-mA load. If other circuits will be used with these dc power sources, then the 220-μF capacitors should be increased ac-cordingly (2200 μF will provide about 65 mA regulated output).