Hello,
The schematic shows a 110 ohm, 10 watt resistor across the heater of V-5, a 6H6. All the tubes are in series and have 300 Ma heaters, so I don't understand the need for this resistor. Why is it necessary to lower the heater voltage on the 6H6?

Tom Ackerman

In some cases, it was found that the 6H6 and other detector tubes work better at a slightly reduced filament voltage. A resistor in parallel with the filament when the tube is in a series string filament circuit will accomplish this. If the tube were in a parallel connected filament circuit, there would be a resistor in series with the 6H6 filament. Maybe someone else can explain why the tube works better with a reduced filament voltage.

Dave