Tube Power Supply Design / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

Tube Power Supply Design

Move Thread

LAN_403

EDY19

Thu Dec 06 2007, 12:49AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I have been working on designing a power supply for a new tube based plasma tweeter. I found a GREAT program that allows me to test many ideas, and monitor voltage and current across all components. The schematic below is my potential design, and with a load of about 1.2kOhms on the 600V output, and the PI filter consisting of a 3H inductor, ripple is less than .25V. My question is, can i put another inductor in the +300V line to smooth that out for the grids? Also, if i were to decrease the value of the 560uf capacitor from +300V to GND slightly, could I obtain a slightly higher voltage for the screens/grids? I am aiming for 350V for this leg of the power supply. The tweeter is the design here:

Using a EL519 tube, EF86, and ECL82.
Also, in the picture, the primary of that transformer is 115VAC, not 15

EDY19

Thu Dec 06 2007, 12:51AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Ooops, forgot the picture...

Hazmatt_(The Underdog)

Thu Dec 06 2007, 09:36AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Your 300V line is going to have fundamental frequency ripple from whatever method you derive your power from.

You're also mixing your grounding schemes, I wouldn't do it this way. You're designing a noisy supply.

I designed a little power supply that's on the old forum somewhere. I took the 120, stepped down through a 12VCT 3A I think, used the 6V for filaments and the other 6V went to another 12VCT but I only used the 6V to get 120 on the other side. After that it went to a tripler and balast resistors for 240-330V range.

If I were you I would use a cascaded multiplier and take a tap off at 300V insted of what you're doing here, that is unless you need more then a few mA of current. But then my question is, how much current do you really need for a plasma speaker?

EDY19

Thu Dec 06 2007, 04:08PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

The original design calls for a 120VA transformer, so I was thinking <200ma for sure on the current. The grid/screen supply (~350V) should need very little current however. I just don't know that much about tubes, so I'm in a whole new territory without using MOTs and 811As

Those leave a little more room for error

Maybe I'll think about a switching power supply- I'll have to check around for some schematics, but having these two voltages adjustable might be a handy feature. What do you think? I'm not aiming for an all tube design, so I wouldn't mind the lessened weight of Solid state!

Hazmatt_(The Underdog)

Thu Dec 06 2007, 11:15PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Well, you might be able to get 200mA @600VDC from a 5 stage multiplier, using 1N4007 and 470uF caps or larger. So your tap point would be after the second stage because the doubliers output more like 2.8x input rather then 2x.
The cascade will also allow you to have the same case/HV gnd which will prevent you from getting nasty shocks of a 2 gnd setup.

The power supply I'm suggesting might not supply enough current, I'd test it up to 200mA but I'm a bit tied up right now. If you want to test it out just do a quickie but be real careful around it, I got shocked by mu supply when testing it and 350V really hurts even at low current.

EDY19

Fri Dec 07 2007, 12:16AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I've done a little research on switching power supplies, and I think I am going to build either 2 half bridges into two separate transformers for (+350V, +~600V) or 2 boost converters after seeing the simplicity of those, and Steve Wards scaled up design. This will allow for a lot less weight and space taken up as well from the power supply. Any comments on what types of SMPS power supply?

Steve Conner

Fri Dec 07 2007, 11:07AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Fender just used a two-diode doubler, and only put a Pi filter on the 350V rail, the 700 is just smoothed by a plain capacitor. There's no reason why you couldn't add a choke and second capacitor to the 700V rail too.

With a SMPS, you might find it hard to keep beat-frequency whistles and aliasing out of the audio. I considered a SMPS for my upcoming tube bass amp project, but I couldn't be bothered, so I'm copying the power supply from the above 300PS instead. I figured that if I already have to lug a 15lb output transformer and at least one 70lb speaker cabinet, another few pounds of iron won't really matter. Fender's power transformer weighed 23lbs(!) but I managed to get a toroidal one that weighs about half of that.

The only problem with the Fender design is that the 350V rail is halfwave rectified. So all the current drawn from the 350V rail flows as DC through the transformer winding, which can make it buzz. I'm worried about that, since I have a toroidal P.T. and I know they hate DC. With your design, both rails are full-wave rectified.

EDY19

Fri Dec 07 2007, 04:41PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Thanks Steve! That is just what I needed to see - +700V and +345. I'm going to my first hamfest this upcoming saturday, so I'll look around for a ~250-260V transformer at a couple hundred milliamps- i could probably find an 1:2 isolation tranformer with multiple primaries, and use a primary rated for a slightly lower voltage. I already have some extra capacitors (400V, 560uf) that should be great for the doubling capacitors, too. Would it be possible to decrease the value of one of the doubling capacitors in order to increase that 300V in my schematic? And lastly, I'll probably add some resistors across the caps as bleeders.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob