CTC-2B Ballast

[wa2ise]

If the heater string adds up to around 84V, you can use a rectifier diode, without any filter cap, to effectively drop the 120VAC line. This saves the energy that would be wasted as heat. Remember, it's power = volts squared over resistance. The diode cuts the power in half, and the effective voltage is 120V times the square root of 2 (from the half) which then = 84V.

[Electronic M]

Originally Posted by wa2ise

If the heater string adds up to around 84V, you can use a rectifier diode, without any filter cap, to effectively drop the 120VAC line. This saves the energy that would be wasted as heat. Remember, it's power = volts squared over resistance. The diode cuts the power in half, and the effective voltage is 120V times the square root of 2 (from the half) which then = 84V.

You missed the part where it is mentioned that the Ballast in the CTC2B (a parallel heater transformer powered set) is used as a DC B+ divider....It has to remain a resistance based divider....Unless of course nick wants to go with LM317 DC to DC regulators. For the drop he'd need at least 4 in series (I've ran those chips in series as well as parallel before) to safely drop 115V (each device can only drop 40V max between input and output terminals). The biggest hurdle of using the LM317 is what to use as a ground reference...You might be able to keep the 430 ohm and reference the whole shebang to the centering terminal (thus replacing only the 800 ohm with LM317s), but if you want to eliminate all resistors you would need a ground reference.

[wa2ise]

Originally Posted by Electronic M

You missed the part where it is mentioned that the Ballast in the CTC2B (a parallel heater transformer powered set) is used as a DC B+ divider....It has to remain a resistance based divider....Unless of course nick wants to go with LM317 DC to DC regulators. For the drop he'd need at least 4 in series ...

The LM317 is a linear voltage regulator, in which case the voltage drop produces waste heat anyway. So you might as well use power resistors. If you have DC-DC converters (essentially a switching power supply) that might work, if there's no RFI from the switcher. But if you want to keep the set as close to the technology of its day, the resistors would be the way to go.

Some TV sets used the audio output tube as a voltage dropper for the set's IF strip.

[walterbeers]

The Ballast in my 21CT55 was good, (other than being rusty), measuring very close to the 800 and 430 Ohms. Actually it's just 2 high wattage resistors inside of a plug in unit, with a jumper between a couple of pins. If you can I'd just see if you could find a couple of 20-25 watt resistors and put them inside of the ballast, although I suppose space could be a problem. I painted mine with high temp silver paint for appearance.