Scope Clock Newbie Question About Heat

[Paul Atkin]

I am in the middle of a build for a my first small Scope Clock kit using a Mullard DP7-5 tube, haven't yet powered it up because I am waiting on a tube socket.

Question, do these tubes get hot?  I am designing a holding frame for the tube and planning to 3D print it in PLA.  Obviously no good if the tube generates any significant heat, especially around the electron gun area.

My past experience is limited to nixie, neon and VFD displays.

Any experiences?

[gregebert]

Most of the heat for the CRT should be from the filament; This is what I found online

Vf 6.3 Volts / If 0.31 Ampere / Indirec

That amounts to about 2 watts; the anode power is much smaller.

If you provide louvers on the case so that natural convection can remove the warm air, you should be OK as long as there is some exposed glass surface area around the neck for heat conduction.

[Paul Atkin]

Great thanks, so something like this should be no problem?

[gregebert]

Nice !

I suggest some padding where the glass contacts the plastic. Adhesive-backed foam tape, which is sold in home improvement stores for door insulation, should work well for a few years.

[gregebert]

BTW, I have used PLA for mounting small power transformers, with no issues. I just put a lot of ventilation holes on the sides and bottom for convection current.

[Paul Atkin]

Thanks very much.  Noted about the clamp, I will leave the diameter about 1.5mm over the tube diameter and use foam as you suggest.

If anyone is interested, I bough the kit from Jan Wuesten at

https://www.die-wuestens.de/r5.htm

The documentation is a little challenging but he has been extremely helpful setting me in the right direction.  Hope to get the pixies flowing through this kit in a few days.

On Wed, Jan 23, 2019 at 2:37 PM gregebert <greg...@hotmail.com> wrote:

BTW, I have used PLA for mounting small power transformers, with no issues. I just put a lot of ventilation holes on the sides and bottom for convection current.

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[Oscilloclock]

Similar to the foam idea, in my clocks I use a 2mm thickness of silicone between the (cast acrylic) clamp and the neck of the tube. The silicone rubber should last decades, it is translucent for good looks, and it seems to shield the heat from getting to the acrylic clamp.

As for ventilation, my completely sealed acrylic CRT units don’t seem to have a problem - even the 8mm thick acrylic tube does seem to conduct the 2-3W heat out well enough, I have opened up the case after days of running in summer and it’s just a bit warm in there.

Nice mounting design, enjoy the build!

[Mike Mitchell]

I built two of Grahame Marsh's scope clocks using a wooden base, as shown here:

https://www.dropbox.com/sh/rldue6seyzty9ju/AAB8kECNtxuRSKLGU4rF6Pm3a/Photos/MikeM?dl=0&subfolder_nav_tracking=1

A simple acylic case fits over the base.  I used black felt to line the wooden supports.  I didn't need to clamp the neck in place, the weight of the 5" tube is sufficient.

The interior of the case gets to just over 80 degrees Fahrenheit during operation.  The only vents are under the black box on the base.   

You can find out more about Grahame Marsh's scope clock kit at 

http://www.sgitheach.org.uk/scope3.html 

He has an acrylic case design of his own.