variac question

[yagosaga]

I operate every vintage hybrid tv set with a variac. Here in Europe, vintage tv sets do not have a mains transformer. Filaments are heated by serial mains voltage. And when they are cold, they are overheated by the full mains A.C.. This reduces the lifetime of the tubes. So I use a variac and watch the tubes' heating while power on.

- Eckhard

[wa2ise]

Another way to drop the line voltage is to use a power resistor, inserted in the power feed, that, with the current the TV set draws, drops you about 6V. The set usually has a label on the back telling the power consumption, say it's 175W. Divide that by 117V, and that gets you an approximation of the current draw. Here we get 1.49 amps, call it 1.5 amps. Ohms law then gives us 6v/1.5a = 4 ohms. Now how much power rating for that resistor? Vsquared/R = P, 36/4 = 9 watts, a 10W resistor would do. Or use a 20W resistor so it won't get as warm to the touch. Hide it inside the cabinet.

A resistor will reduce the turn-on inrush currents you get from the set's cold tube heaters and such.

Did you check your voltage with a load ?

If the voltage sags more than a half volt with a 100W load, there's likely a house wiring defect that needs to be corrected.