Easy way to get 12VDC/150mA to power some LEDs

[tubesornothing]

I am looking for an easy way to get 12VDC/150mA to power some LEDs.  I would like to avoid rectification/filter if possible. Even if I did use the heaters, they are offset by 60+ volts and that will be too many volts to ground for my little LED display.  I dont have a 5V tap or Bias tap either.

If I use a voltage divider from the B+, I am guessing that it wont drop the B+ node voltage too much?!?!  What messes me up, is if I want 12V/150mA of B1 (which is 448V) I would need a 448V/.150A = 3k resistor.  That's going to totally kill my B+.

Whats wrong with my math here?

[PRR]

> Whats wrong with my math here?

Nothing.

The problem is the word "easy". There is NO "easy" way to make low voltage high current from a high voltage low current DC source.

Yes, a 3K 68 Watt resistor is "easy", IF your power supply can spare another 150mA. Tube amps usually eating 80mA-200mA, with little to spare, you just can't parallel another 150mA load, and then it would be stupid/hot to shuck 97.5% of that as waste heat.

(Actually I think your total is 448V, you want 12V, your resistor is really figured as 436V not 448V. But no real difference.)

What IS your total amp consumption? If you just need 150mA, and you have a quad of cathode-bias 6V6, your tubes are passing ~~150mA already, and they would work just as fine with 436V as the full 448V. Tap the LED box into the cathode circuit. But I don't think that is what you have.

What kind of LED box really needs 12V at 150mA?? That's a LOT of LED power, unless you are using bike-lights or something. Most stage-amp pilot light LEDs are plenty bright with a few volts at 10mA each. I have a frikkin binary 20-LED clock here says it uses only 9V at 150mA, and I think that's high.

12V 0.150A _is_ a normal rating for some incandescent pilot lamps.

[tubesornothing]

Hey thanks, well that at least explains the numbers I was getting.  Yeah 150mA was way out of whack, I am not sure where I got that from.  The cathode circuit - I like that.

[sluckey]

I am looking for an easy way to get 12VDC/150mA to power some LEDs.  I would like to avoid rectification/filter if possible. Even if I did use the heaters, they are offset by 60+ volts and that will be too many volts to ground for my little LED display.

Are you talking about just a simple LED with series limiting resistor? If so, use the heater circuit and just float the LED circuit. DON'T reference to ground and the LED will never know or care that the 6.3VAC is riding on 60VDC.

But, if you need 12vdc/150ma to power some LED module that also has active electronics (something like a bar Vue meter, or 7 segment display/driver) you may want to consider a dedicated ps.