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Tubes and Hybrids / Re: Reduce signal from preamp.
« on: January 21, 2021, 02:21:35 PM »
12a?7 valves have a 12v6 heater between pins 4 & 5 and a centre tap on pin 9. for 6.3 v common pins 5 & 6 and feed supply between these and pin 9. AC or DC doesn't matter.