Author Options:

running vacuum tube filaments on dc and getting 10 volts from 2 5 volt wires from a atx? Answered

i am going to run a 10 volt filament on the +5 volt and +5 volt to get a combined power of 10 volts. First of all will running the filament on dc hurt it? Also the tube takes 10 amps, so will the +5 and +5 power supply be able to cope with it? ( it is a atx power supply) also how do you wire 2 +5 volt wires with a common ground to get 10 volts



Best Answer 8 years ago

Use the +12V supply and drop it down to 10V.  Te reason is that while you could use the +5V and -5V lines together to get 10V, only the +5V line can supply enough current.  The -5 only supplies an amp or two at most, so you might burn it up by trying to draw 10 amps. 

As gmoon suggests, use a couple giant diodes in there to soak up that extra voltage and you should be good to go.

You can't be right on that,surely, or maybe? What tube is it?


well as i said earler in a comment it is 2 803 tubes, 5 amps each, but ther is a tube that takes 10 volts, ten amps, the 833a tube

I must look up more on tubes, thanks for the information (just did look 'em up). What are you using for your high voltage source?


i'm using a villard cascade to get 2kv. i might need to make it current limented, do you know if i do? ( i would make it pass only 6 amps so it would give 720 watts, 20 more than both tubes)

My limited knowledge of thermionic valves says you don't need current much on the HV side, more the electric potential. In a vacuum tube you'll not pass much current with cold electrodes. On the LV side I think it'll limit it's self?


.  If they have a common ground, you can't get 10V out of two +5V supplies. You can if the supplies float or if you have a +5 and a -5 supply.

.  If that was supposed to be 10V, you can regulate the 12V output, but you're going to need a fairly hefty regulator to handle 10A (120W).
.  As a very rough rule of thumb, at least half the power in a PSU will be on the 12V rails. Eg, a PSU advertised as being 500W will have at least 250W (21A) available on the 12V buses.

No problem with DC filaments.

You can string some silicon rectifier diodes in series to drop a couple volts off your 12V supply.

Each SI diode will drop approx 0.7 volts, so three diodes (12V - 3*0.7 = 9.9V). If three is too much, then try two.

Since the forward voltage drop over each is only 0.7 volts, each diode should "only" dissipate ~3.5 watts (@ 5 amps.) If 1N4007 diodes don't cut the mustard, use two or three 1N5408 diodes, which are 3A @ 1000V.

There are tricks to heatsink diodes, too. Like drilling a hole in a penny and soldering it to one end of each diode (just don't ground each penny like a typical linear IC heatsink! Keep each one electrically isolated.)

Oopps! Two 5V tubes, so 10 amps total. So ~7 watts per diode.

Still reasonable, but they will get hot...

Running a tube on DC will work fine. 

I'm not sure about how to use the atx power supply though some of them are finicky.

What tube are you using that takes 10 amps?

What is your project?

well i'm using two 803 for a vacuum tube tesla coil