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Ash Small

Fri Jan 25 2013, 06:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

This is the circuit I intend to try:

I'm planning on trying ~250uF-450uF, and a fast diode. All the resistor has to do is discharge the cap between spikes. It should have negligible affect on the rest of the circuit, as far as I can see, if it's value is reasonably high, but I haven't built it and 'scoped it yet.

I've not tried it yet, but I plan to as soon as I finish the project currently on my breadboard.

Any comments from other forum members will be most welcome.

EDIT: I'm actually going to use it with a single transistor circuit. I'm not sure whether the two transistor circuit would benefit from a freewheeling diode. I don't think it serves any purpose with a centre tapped primary, but unless I build it and 'scope it I can't be certain.

Ash Small

Sat Jan 26 2013, 01:40PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ruskie wrote ...

With the first 3055 set I replaced, I did notice that there was a difference in gain- only about 60% of the original set. That set didn't last long.

Sounds like they possibly weren't fully turning on, but the gain can vary quite a lot from one set to another. Have you tried 'scoping accross C and E on the latest set of 2N3055's to check for spikes?

Maybe try shielding the cable from the multiplier to the head? (just a guess)

Ruskie

Sat Jan 26 2013, 01:57PM

Registered Member #9290 Joined: Sat Jan 05 2013, 03:42PM
Location:
Posts: 60

Ash Small wrote ...

...Have you tried 'scoping accross C and E on the latest set of 2N3055's to check for spikes?

Maybe try shielding the cable from the multiplier to the head? (just a guess)

Can't do as I don't own a scope. The only shielding the HV lead has at present is a layer of vinyl over it (this is in addition, of course, to the insulation already present on a HV multiplier lead).

Ash Small

Sat Jan 26 2013, 03:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ruskie wrote ...

Can't do as I don't own a scope.

Well, you could measure the accumulated voltage accross the transistor by removing the resistor from the snubber circuit I posted above, and seeing what voltage the capacitor charges to over time, but I'd recommend adding a resistor in series with the diode, and using a smaller value resistor. You won't be able to see if the diode is fast enough without a 'scope, but you could just try using the fastest you can get.

I paid Â£20 each for my 'scopes, I have two. get one from Ebay, or somewhere, one designed for fixing TV's will be fine. There are loads on the surplus market, or buy a new cheap digital USB one. (Personally I'd go for an old analogue one)

Tony Matt

Sat Jan 26 2013, 08:47PM

Registered Member #3700 Joined: Sat Feb 19 2011, 12:59PM
Location:
Posts: 107

Hi Ash !

Let me know what software you have used to make the diagram

Thanks

Ash Small

Sun Jan 27 2013, 01:23AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Tony Matt wrote ...

Hi Ash !

Let me know what software you have used to make the diagram

Thanks

A twenty year old version of TurboCad. Any CAD software should do it, though. It only took me a couple of minutes. I usually spend a bit more time on them to get them a bit neater.

Ruskie

Sun Jan 27 2013, 04:41PM

Registered Member #9290 Joined: Sat Jan 05 2013, 03:42PM
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klugesmith

Mon Jan 28 2013, 08:10AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Ruskie wrote ...
. What I might do in a pinch to save these transistors is put a light bulb in series on the input AC line. I noticed the other day that a 100 watt bulb was close and wouldn't let voltage/ current go any higher after a certain point, so I think 150-200 W bulb will work..... for now. Of course, I have to cover the bright monstrosity since it will defeat my point of camera capturing x-rays from the screen.

Instead of investing in uncommonly high-wattage lamps (with regular screw base?),
how about wiring two or three sockets in parallel? Then with an assortment of various wattage lamps, you can finely tune your ballast.

Especially if your primary interest is in radiography, and that your first adequate HV power solution will be your last.

Ruskie

Mon Jan 28 2013, 01:18PM

Registered Member #9290 Joined: Sat Jan 05 2013, 03:42PM
Location:
Posts: 60

Ruskie

Mon Jan 28 2013, 04:24PM

Registered Member #9290 Joined: Sat Jan 05 2013, 03:42PM
Location:
Posts: 60

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