I've only been registered here a short time, but it seems like some knowledgeable people are on here. I have a question, first prefacing basic operation. This is an area on the schematic of a receiver that was on a WWII American bomber. The radio was operated off the 24-28 system running throughout the plane. That voltage ran the self-contained dynamotor (generator) that provided the 235V B+ for the radio. The tube heaters were run straight off the 24-28 airplane electrical system. The tubes were all 6.3 volt heaters, all using 300 millivolts of heater current each, except the final audio tube 6K7 with took 400 millivolts. Studying the area highlighted in pink, it would seem that the 2 heater strings get 25+ volts, AFTER Resistor 76-A brings down the aircraft 28 volts down to the 25+ volts each heater string needs. We have 2 series strings, in parallel.
Now to my question: Would Resistor 76B be there because the output tube needs .4 amps, so it needs a little extra juice provided by R-76?
Then what if I want to put a 6V6 tube in place of the 6K6, and the 6V6 takes .45 amps at 6.3V? How would I calculate resistor value then? Thank you. PS, btw, I already know I'll have to change grid bias also, but that's not my question.
Now to my question: Would Resistor 76B be there because the output tube needs .4 amps, so it needs a little extra juice provided by R-76?
Then what if I want to put a 6V6 tube in place of the 6K6, and the 6V6 takes .45 amps at 6.3V? How would I calculate resistor value then? Thank you. PS, btw, I already know I'll have to change grid bias also, but that's not my question.
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The 190 ohms is in parallel with the 3 x 0.3A heater string.
It's just resistors in parallel.
Calculate the resistance of the heaters then resistors in parallel calculation.
Hint - online calculators perform resistors in parallel calc.
It's just resistors in parallel.
Calculate the resistance of the heaters then resistors in parallel calculation.
Hint - online calculators perform resistors in parallel calc.
In the schematic the resistance of the 400mA heater would be 15.75 ohms. You want the rest of the circuit to equal 3 times that, ie 47.25 ohms but the three others equal 63 ohms on their own.
I am not able to do the math on this, which is why I ask. I was a poor student in school and was never tested for dyslexia as a possible cause. Instead they spent fortunes on eye doctors. I understand theory and terminology in chemistry, mechanics, and all kinds of sciences. But when I try to actually do the math, the numbers criss-cross. Thank you.
Thank you. I have no idea why I put the "d" in "question" in the head topic. And then failed to post the graphic with the first post of it. I deserve no answer. How is it that I can understand mathematics and so many other studies so well, but cannot trust my own math on paper? Oh,well. Regards all.