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dc high voltage supply (120 ~ 160).

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Duality

Wed Dec 19 2012, 05:57AM

Registered Member #1951 Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105

Hey all :)
I want to design/make a voltage supply for my tubes, (vacuum tubes/valves)
But I have no idea where to start,
first I was thinking of connecting two transformers in a way that one would step down mains, and then the second would step up back to
the needed voltage, but I don't have to many transformers laying around, so I though maybe
make some kind of switched power supply ?
I have some power mosfets laying around irfp460 if IIRC
Also I have two UPS circuit boards that has a few H bridges on it, maybe could use that.

Any way I hope someone can help me out or point me in a direction.
(also I hope I am allowed to post it here)

Greetings,
Rob

Patrick

Wed Dec 19 2012, 06:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

what final voltage do you need?

you can get 160VDC by rectifying 120VAC...

Duality

Wed Dec 19 2012, 07:13AM

Registered Member #1951 Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105

oh wait didn't I include that bit ... It's in the title :) but we got 240AC here. so no rectifying mains here.
voltage needed is about 120 to 160 maybe even 180 ish ? (coolest would be if it were adjustable.)

ScotchTapeLord

Wed Dec 19 2012, 07:36AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

You could use a commercial voltage converter for using American appliances on 240. Just make sure the wattage is sufficient with some headroom.

Or get higher voltage tubes and rectify mains! ;)

Sulaiman

Wed Dec 19 2012, 09:10AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

A very versatile but quite expensive approach;
A variac e.g.

A 240:2x 115Vac isolating transformer e.g.

These are just eBay examples, look around for better prices.
Connect secondaries in series for 0-230 Vac, in parallel for 0-115 Vac.
Add a bridge rectifier and electrolytic capacitor(s) for 0-160 or 0-320 Vdc.
Add off/on switch, fuse from variac wiper and an enclosure.
Add a low voltage output transformer, rectifier, capacitor etc. for a variable low voltage psu.
You can 'earth' any output due to the isolation transformer.

At the other end of the cost spectrum,
any 230 Vac mains transformer that has two 115 Vac primaries can be used as an auto-transformer

for 230 :115 Vac NON-ISOLATED.
Add bridge rectifier and capacitor(s) for c160 Vdc
BOTH +DC AND -DC SHOULD BE TREATED AS MAINS LIVE.

Duality

Wed Dec 19 2012, 09:52AM

Registered Member #1951 Joined: Sun Feb 01 2009, 01:59PM
Location:
Posts: 105

Sulaiman,
actually I got a variac, but i don't like using it,
cause now and then it wil blow the fuses when plugging it in.
can do 240 at 10A.

johnf

Wed Dec 19 2012, 06:49PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Duality
Variacs can remember the magnetic flux when turned off
ie if you switch off at the peak of a mains cycle the core remains magnetised until the next turn on. if the mains is at the opposite cycle peak at turn on then the magnetic forces cancel and the current in the variac winding is equal to the DC resistance of the winding --usually very low --a few ohms --so for that first half cycle 50 to 150 amps is not unusual --a great fuse tester
A surge preventing NTC resistor in series with the input to the variac can alleviate this
ps you only fuse a variac output not the input for this reason

Also if you use the variac you should use an isolating transformer as well to isolate yourself from the mains

Proud Mary

Wed Dec 19 2012, 09:28PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Nothing very useful can be said about a power supply for thermionic valves without some idea of the current needed by the valves in question.

Generally speaking, power supplies in consumer electronics of the thermionic era were very simple and used few components. Cheap AC/DC radios had no transformer at all - HT+ was produced by a half-wave rectifier in series with the Live AC or DC+ mains line, and the heaters were all connected in series with a big ceramic dropper resistor wired directly across the mains.

Cheap AC only consumer electonics often had a transformer supplying 6.3V to the valve heaters, while a half-wave rectifier (valve or selenium) was connected directly to the Live AC line to produce HT+, while the Neutral line was connected to the chassis - the very popular but hazardous 'live chassis' technique.

So you must decide what circuits you want to run before you decide what power supply would be best for them to work well.

Adam Munich

Wed Dec 19 2012, 09:29PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Just pick something large enough so that Xc doesn't become an issue. This isn't too efficient for large loads though.

Divider

$F8c303a4844efb38eaa2b65c1d92b441$

Andre

Fri Dec 21 2012, 04:21PM

Registered Member #6921 Joined: Wed Sept 26 2012, 07:47PM
Location:
Posts: 109

you can do everything with the vacuum tubes even the bridge rectifier, and you can adjust the voltage by adjusting the filament on the tube, vacuum tubes are high power mostfet,
here is a video tutorial on vacuum tubes and how they work:

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