Selenium rectifiers

[bandersen]

Right and P is also I2 X R. So if B+ is drawing 320mA, then you'll have (0.32 * 0.32) * 39 = 4 watts out of that resistor so a 5W should be OK, but maybe 7W for a little overhead. Or use a smaller 5W resistor like 33 or 27 ohms.

[Findm-Keepm]

Originally Posted by bandersen

Right and P is also I2 X R. So if B+ is drawing 320mA, then you'll have (0.32 * 0.32) * 39 = 4 watts out of that resistor so a 5W should be OK, but maybe 7W for a little overhead. Or use a smaller 5W resistor like 33 or 27 ohms.

He's 20V low, and the 39 ohms is dropping that. My original calculations called for a ~13 ohm resistor. (see post 27, page 2) Take three 39 ohm resistors, parallel them, and place them in the circuit. That'll give you the proper (lower) voltage drop, which should give you the proper B+, and plenty of overhead on the wattage. .33A X 13 = 4.29W, and you've got (3) 5 watters in parallel.

[Findm-Keepm]

And Tim, if you need more resistors, lemme know. I've got my dad's old stock of resistors, and yes tons of diodes too. Save your money on parts and buy sets....


Cheers,

[bandersen]

Originally Posted by Findm-Keepm

He's 20V low, and the 39 ohms is dropping that. My original calculations called for a ~13 ohm resistor. (see post 27, page 2) Take three 39 ohm resistors, parallel them, and place them in the circuit. That'll give you the proper (lower) voltage drop, which should give you the proper B+, and plenty of overhead on the wattage. .33A X 13 = 4.29W, and you've got (3) 5 watters in parallel.

Minor correction - it's current squared times resistance or (0.33 * 0.33) * 13 or 1.5 watts like you calculated earlier. So only 0.5 watts per 39 ohm resistor.

[Bill Cahill]

I don't know where you guyes are getting your fancy calculations, but, you both are way off.... I will state for a fact. Every one tube record player I have run into has had a five watt resistor on selenium.
Every simple five tube radio, five, to ten watts.
I have NEVER seen any BW tv with anything less than ten watts, and, sometimes as high as twenty five watt resistors on the seleniums.
Further, Tim made it clear it was burning out five watt wirewound resistors. And, you think a half watt resistor is going to drive an entire tv???
Wake up, guys.. Your fancy calculations are really amiss.....
Bill Cahill