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ms660 · 4th Dec 2019, 8:22 pm

According to a schematic I'm looking at, on FM, the voltage given for the main HT at the reservoir capacitor is 273 volts, the screen grid voltage on the output valve is given as 220 volts, that's a voltage difference of 53 volts, the resistance of the hum cancelling section of the output transformer will be small compared to the 1.3k resistor so can more or less be ignored, that leaves power dissipated in the 1.3k resistor as Vsquared/R which equals 53squared/1300 which equals 2.24 watts approx. which is within the rating specified in the schematic and well within the rating of the 5 watt resistor under normal conditions.

Lawrence.

4th Dec 2019, 8:22 pm	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Grundig 7070W hot resistor. According to a schematic I'm looking at, on FM, the voltage given for the main HT at the reservoir capacitor is 273 volts, the screen grid voltage on the output valve is given as 220 volts, that's a voltage difference of 53 volts, the resistance of the hum cancelling section of the output transformer will be small compared to the 1.3k resistor so can more or less be ignored, that leaves power dissipated in the 1.3k resistor as Vsquared/R which equals 53squared/1300 which equals 2.24 watts approx. which is within the rating specified in the schematic and well within the rating of the 5 watt resistor under normal conditions. Lawrence.