[Amps] 3D Printed ABS Plastic for Chimneys?

[N7EME]

Hi Dieter,

I built a 6 Meter Amp using the GS31B and made my own chimney using 
fiberglass resin on a 4 inch diameter
form. I covered the form with wax paper so I could get the fiberglass 
chimney to release from the form. You
can buy the Bondo fiberglass material and Bondo fiberglass cloth at your 
local automotive store. I made the
chimney about 12 inch long for some future amp designs. Fiberglass is an 
excellent insulator and resists high
temperatures. The chimney for my 6 meter amp is actually attached to the 
top cover of the amplifier and fits
snugly around the GS31B plate nicely. My solution for what its worth.

73
Jerry - N7EME


On 11/23/2016 1:06 PM, Paul wrote:
> 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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