05-22-2026, 11:01 AM
Hi Joe,
One thing to be cautious about is that the filament voltage of 7.5 volts is derived from a voltage divider from B+ (R101A and R101B). If you replaced the selenium rectifier with a silicon diode (1N4007 or equivalent) the B+ will now be about ten volts higher. In addition, this circuit was designed for 117 volts from the mains and my house gives me 122. That's an additional five volts. You should consider increasing R100 to compensate for the increase. I also add a 1 watt zener diode to the 7.5 volt connection point to protect the filaments.
One thing to be cautious about is that the filament voltage of 7.5 volts is derived from a voltage divider from B+ (R101A and R101B). If you replaced the selenium rectifier with a silicon diode (1N4007 or equivalent) the B+ will now be about ten volts higher. In addition, this circuit was designed for 117 volts from the mains and my house gives me 122. That's an additional five volts. You should consider increasing R100 to compensate for the increase. I also add a 1 watt zener diode to the 7.5 volt connection point to protect the filaments.
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