03-13-2017, 02:59 PM
Hi Walt,
Here's how it works.
The tubes that start w/#7 equal 6.3v you have four of them = 25.2v
The tubes that start w/#35 equal 35v you have two of them =70v
This makes a total of 95.2v
The AC line voltage is about 120v. So if we hooked the heater directly across the AC line we would have about 25v too much.
Resistor #18 is used to drop the "extra" 25v. It equals about 180 ohms.
All the tubes are happy!!!!
When you substitute the 35A5 w/a 50A5 ( the 50A5 equals 50v instead of 35) it increase the needed voltage by 15v (50-35=15) This means instead of needing 120v now you need 135v.
If you put a jumper across #18 two things are going to happen. One dial lamp won't work any more. And w/the 50v tube in the circuit now the total is about 109v still a bit too low to power w/120v
When you recalculate #18 to only drop the "extra 15v" is total resistance equals 100 ohms. You'll want to leave the value of the left half of #18 the same as it is used to balance the current though the dial lamp.
Sorry for all the math!
Here's how it works.
The tubes that start w/#7 equal 6.3v you have four of them = 25.2v
The tubes that start w/#35 equal 35v you have two of them =70v
This makes a total of 95.2v
The AC line voltage is about 120v. So if we hooked the heater directly across the AC line we would have about 25v too much.
Resistor #18 is used to drop the "extra" 25v. It equals about 180 ohms.
All the tubes are happy!!!!
When you substitute the 35A5 w/a 50A5 ( the 50A5 equals 50v instead of 35) it increase the needed voltage by 15v (50-35=15) This means instead of needing 120v now you need 135v.
If you put a jumper across #18 two things are going to happen. One dial lamp won't work any more. And w/the 50v tube in the circuit now the total is about 109v still a bit too low to power w/120v
When you recalculate #18 to only drop the "extra 15v" is total resistance equals 100 ohms. You'll want to leave the value of the left half of #18 the same as it is used to balance the current though the dial lamp.
Sorry for all the math!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got it!
Terry
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