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Grenadier's big thread of RÃ¶ntgen related shenanigans

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klugesmith

Fri May 27 2011, 03:49AM

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

Nice work.

Grenadier wrote ...
Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...

For that example, in the likely case that mA meter's full scale voltage is not more than 200 mV: Shunt the mA-meter circuit at the HV end with hefty diodes in both directions, and a capacitor. Then at the control end, even if meter is disconnected there's no HV. The shunt should be able to withstand the maximum HV current under fault conditions, such as an unexpected arc in parallel with your Coolidge tube.
A similar approach can protect your kV-measurement circuit. In that case, if full-scale meter current is in the 10-to-20 uA range, the FS meter voltage may be high enough for a regular protective shunt diode to conduct significantly.

Xray

Fri May 27 2011, 02:42PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

If the meters are working OK the wires will be at low voltages, <10V, however if a meter goes open circuit then those wires are no longer pulled down to ground and will get quite hot. Example, the mA meter is in series with the tube and ground. If it goes open circuit then one side is +HV and the other is ground. Maybe some MOVs could protect things...

If any point along the mA circuit should open, then the open circuit will arc like a spark gap when the hv is energized. In fact, some older X-ray heads have a small spark gap mounted right at the mA terminal on the head to handle that particular situation. Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head. A typical neon bulb will fire at around 85 volts, and it should be able to handle the current from your CW multiplier for some time period.

Nice job, Adam!

klugesmith

Fri May 27 2011, 03:47PM

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

Xray wrote ...
... Newer models use a commercially available gas-filled voltage snubber (I'm not sure if that's really what they are called). It's bascially a neon bulb. And that's what you can use in your X-ray head.

Excellent suggestion - a single, inexpensive, very robust part.
The name is gas tube surge arrestor. e.g.

The ones pictured can probably handle short pulses of over 1000 amps.
I can send you a few that look like three-terminal neon lamps.

Adam Munich

Sat May 28 2011, 04:05PM

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

That is a clever idea using the neon lamps as protection, sure have enough of those. I've got a couple 1kV gas tube surge arrestors, I've always wondered whether or not a mark generator could be made 100% reliable by using those things in series instead of spark gaps.

I found this nice ceramic octal base that I could use for the control box's connection, but as for the head I'll have to use a plastic one as I have no more ceramic ones. I just need to find a pair of octal bases or tubes, all my tubes are nice GE and RCA ones (which I'd prefer to not destroy). I'll need to stain my box and try not destroy it...

Anyone else notice that my posts sound more intelligent during the day?

Adam Munich

Mon May 30 2011, 03:15PM

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

Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.

Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?

Ideas plz!

Xray

Mon May 30 2011, 05:00PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

Despite my best efforts, the stain looks like crap. Apparently this is just bad wood, grown and harvested in a hurry. My only option now is flat black rustoleum and some lacquer over that to make it nice and shiny.

Of course I could always do a 2 color design... if that is the case what colors and what design? Baby blue and white maybe?

Ideas plz!

Back in the "olden days" (before MY time!) electronic equipment control panels were painted with a textured paint called "crincle", and the prefered color was black. Then in the 1950's and 1960's, they were using a textured paint called "hammertone". and the prefered color was gray. Either of those two paint styles should hide most of the grain and defects in the wood. And that type of paint will give your project a vintage look. Both of those textures are still available from paint manufacturers.

Adam Munich

Mon May 30 2011, 05:22PM

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

Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)

Xray

Mon May 30 2011, 05:49PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

Problem is you need to bake those paints to get the effect, and putting pine in a 200* oven isn't exactly the best thing to do. (sap... everywhere!)

Actually, no you don't need to bake the paint. It comes right out of the can that way. Go ahead and Google "hammertone paint". There are also many other types textured paints available at most hardware stores, if that's the direction you want to go.

Adam Munich

Mon May 30 2011, 08:03PM

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

Got back from home depot, every hammer on or wrinkle paint they had needed a bake.

I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.

Xray

Mon May 30 2011, 08:27PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

Got back from home depot, every hammer on or wrinkle paint they had needed a bake.

I'm just going to do a 2 color thing and then clearcoat, but before that I'm going to layer the primer on (sand between coats) until the wood grain can't be seen anymore.

Here are two types of "hammered" paint made by Krylon:

Neither of them requires elevated temperature to cure.

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