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Re: [Amps] 3D Printed ABS Plastic for Chimneys?

To: "Dieter Kedrowitsch" <>, <>
Subject: Re: [Amps] 3D Printed ABS Plastic for Chimneys?
From: "Jeff AC0C" <>
Date: Wed, 23 Nov 2016 14:02:41 -0600
List-post: <">>
There's not an issue with RF as you suspect assuming the pigments or any additives in the ABS are not RF conductive - but the heat is a problem. Pure ABS is a low temp material and that tube is going to melt that about the first time you warm it up. And ABS resin with common additives is still going to have a melt temp (HDT) way too low.

The safe bet is to use automotive silicon turbocharger hose. You cannot melt it and it's not RF conductive. About $20 for a 1' length of 4" at the performance car parts jobber near you.


-----Original Message----- From: Dieter Kedrowitsch via Amps
Sent: Wednesday, November 23, 2016 1:19 PM
Subject: [Amps] 3D Printed ABS Plastic for Chimneys?

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:
Thanks and Cheers!

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