This seems to be a very simple way to lower a Voltage, and the needed capacity is found by using Xc=1/2 Pi F C, where C is in Farads, and 1/2 means "one over 2 pi". I am bothered by the fact that large, heat producing resistors are used instead of capacitors in just about every application. The capacitor found in a motor is to produce a phase shift between the starting and running winding, to get a single phase motor turning in the first place. Again I ask, why aren't capacitors used to drop Voltages more??
:Me again, I found my calculator and determined that your 5Uf cap is 530.5 Ohms at 60 Hz.
Lewis L
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Resistance line cords appeared in pre-war AC/DC radios. Suitable non-polarized film caps then would have been very large, physically, and expensive - if available at all.
Also, using a voltage dropping cap, the radio would operate on AC only - and there were DC utility systems then. I don't know if this was a consideration, though.
The formula for calculating the required Xc given above isn't quite the whole story. The value Xc is 90 deg out of phase with the resistive impedance of the filaments - so a little trig is necessary.
:::Hello I was reading about resistance line cords, installing resistors, using capacitors and well, I did remember I had a window air conditioner that the motor took a dump so I took out the cap and it was 5 uf.....well it works but its of course 2 uf too small......I would like to get the axial lead caps the the person named "dick" has found that have axial leads, small and easy to mount......but who has them...my motor start capacitor is quite large and just doesnt seem to be feasable......anyone know who has these axial 7uf caps?....as far as electrolytics back to back its mentioned of overheating?...well either they do or dont and I am still on the fence as to whether I should try them or not...I havnt seemed to find a surplus place near me yet
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:This seems to be a very simple way to lower a Voltage, and the needed capacity is found by using Xc=1/2 Pi F C, where C is in Farads, and 1/2 means "one over 2 pi". I am bothered by the fact that large, heat producing resistors are used instead of capacitors in just about every application. The capacitor found in a motor is to produce a phase shift between the starting and running winding, to get a single phase motor turning in the first place. Again I ask, why aren't capacitors used to drop Voltages more??
:
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You can replace a resistance line cord with a power resistor, but there may be inadequate room in the set and it will add a lot of heat to the chassis/cabinet.
You can sometimes reduce the amount of voltage drop required by substituting equivalent tubes with higher filament voltage requirements, but the same current draw. Also, adding a diode to the filament string will reduce the effective rms voltage by about 30%.
A resistance line cord, by today's standards, is not acceptable, safety-wise - even if it's in decent shape.
Another approach is to use a transformer to drop the filament string's voltage to the appropriate level.
:capacitors short. resistors open. opening is better than shorting. don't you think?
::Hello I was reading about resistance line cords, installing resistors, using capacitors and well, I did remember I had a window air conditioner that the motor took a dump so I took out the cap and it was 5 uf.....well it works but its of course 2 uf too small......I would like to get the axial lead caps the the person named "dick" has found that have axial leads, small and easy to mount......but who has them...my motor start capacitor is quite large and just doesnt seem to be feasable......anyone know who has these axial 7uf caps?....as far as electrolytics back to back its mentioned of overheating?...well either they do or dont and I am still on the fence as to whether I should try them or not...I havnt seemed to find a surplus place near me yet
http://vintage-radio.com/repair-restore-information/valve_dropper-calcs.html
And here he give you a link to an Excel spreadsheet to calculate everthing.
It works great!!
http://vintage-radio.com/download/vintage-radio-calculations.zip
Very good, Peter. I will bookmark these sites and study them for quite a while. I do have a bit of a funny story concerning a household emergency light with a Ni-Cad battery in it that was charged from the AC mains through a capacitor. I went to test this little light, and as I worked for an airline, our test bench had 400 Hertz for all the test positions. Forgetting about this, I plugged my little light into 400 instead of 60 Hertz, and when the smoke cleared, I no longer had to worry about fixing my bedroom night light. A lot of stuff went to component heaven that afternoon.
Lewis L.