Half-wave Diode Recitifer

[kannibul]

I'm thinking of converting an amp from AC heaters to DC heaters.

Other than using a pair of diodes and a smoothing cap (20uf should do), what else would be needed?

I also can't remember the voltage multiplier - is it 1.4?

[VacuumVoodoo]

It's not as simple as just connecting a rectifier and a cap to the heater winding of the PT.
You have to take into account voltage drop on the diodes and total current consumption.
I use DC heater supply in my amps, full wave bridge rectifier and 33.000uF cap with heater winding rated at 7.2V under full load to compensate for diode drop.

The question: why do you want/need to run heater on DC supply? If it's a question of excessive hum then there are many simple way to get rid of it.

[donnyjaguar]

First off, if you are taking the conventional filament winding off the transformer you will need a full-wave bridge, not just 2 diodes. If the filament winding is center-tapped, and you tied it to ground, you won't have enough DC voltage.

Make sure the current rating of the rectifier is adequate for the filaments. Some amplifiers draw 5A of current, which is well beyond what 4x 1N400x can handle. :)

I think you'll find that 20uF is pretty much useless for filtering at these current levels, 4700uF would be a good start. :)

I would also check the resultant DC voltage once you've affected the changes. I found on one project that I had appreciably more than 6.3Vdc and had to add a low-value resistor to bring it in-line. Running tubes at too high filament voltage will ensure their untimely demise. Ditto for too low voltage.

DJ

PS: I think you mean Vac(rms) / 0.707 to get the peak DC voltage for a capacitor input filter.

[kannibul]

First off, if you are taking the conventional filament winding off the transformer you will need a full-wave bridge, not just 2 diodes. If the filament winding is center-tapped, and you tied it to ground, you won't have enough DC voltage.

Make sure the current rating of the rectifier is adequate for the filaments. Some amplifiers draw 5A of current, which is well beyond what 4x 1N400x can handle. :)

I think you'll find that 20uF is pretty much useless for filtering at these current levels, 4700uF would be a good start. :)

I would also check the resultant DC voltage once you've affected the changes. I found on one project that I had appreciably more than 6.3Vdc and had to add a low-value resistor to bring it in-line. Running tubes at too high filament voltage will ensure their untimely demise. Ditto for too low voltage.

DJ

PS: I think you mean Vac(rms) / 0.707 to get the peak DC voltage for a capacitor input filter.

Yeah, that's one of the calcs I was looking for. (.707)

Basically I'll be building an amp that has 2 12AX7's, and an EL34 (unless there is another commonly-used octal that draws more heater current)