[Amps] 3D Printed ABS Plastic for Chimneys?

[Paul]

Nice looking amplifier Dieter :-)

There doesn't seem to be much temperature headroom if ABS is used for a 
chimney? The GS35B has a max rated anode lead temperature of 200C 
(392F). At work we print ABS at 230C (446F) but the literature I've seen 
suggests an injection moulding or 3D printer heater temperature of 
between 200 and 230C.

Even if the anode cooler is running significantly below 200C, ABS would 
certainly be above its Tg (105C, 221F). Would it matter that the chimney 
went all flexible and floppy?

I used PTFE sheet wrapped round the (GS31B in my case) tube anode cooler 
and secured with nylon screws & bolts.

73 Paul G4DCV


On 23/11/2016 19:19, Dieter Kedrowitsch via Amps wrote:
> Having been bit by the home-brew 3D printing bug I've been considering designing and printing my own cooling chimney for a GS-35B HF linear amplifier I built a few years ago.  Currently the chimney is an off-the-shelf Coleman lantern globe that loosely sits over the heatsink, so I'd rather use something that's more of an exact fit to ensure all my cooling air is forced up through the heatsink rather than around it.
>
> I've read that styrenes like ABS make pretty good RF insulators, better in fact than Delrin or acrylics, so I'm curious to know if anyone has any input on the feasibility of using a 3D printed ABS chimney for high-voltage HF use?  I use high quality pure ABS filaments so I suspect it should be fine.  Does this sound like a safe bet or would I be best to avoid trying it.  Obviously the amp has copious mounts of protection built-in, but I'd rather avoid any potential for fireworks if possible.
>
> This particular amp and runs about 4KV on the plate and is capable of 1500W+ so obviously the ABS chimney would be exposed to extremely high voltages.  For specifics on the amp itself, I documented my build a little bit here:  http://www.w3drk.com/wordpress/?p=208
> Thanks and Cheers!
> W3DRK
>
>
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