PEEK are another option, I know others that have used them in high voltage application PEEK Screws / Victrex Screws
Wow, so many great ideas; that's what I love about this board! I'm on the road today going to DC for work, but I'll check out all the suggestions later. Thanks!
After checking out the options, I'm going with the Laird clips Rod recommended. Newark has them in stock in the US. Thanks, all.
The clips would also allow you to use a "thermal sock" made from SilPad silicone material. It's a tube that you drape over the transistor package. It's designed for ease of assembly.
~Tom
~Tom
We use PEEK in the chem lab, It's great for high pressure tubing and fittings in liquid chromatographs, and even some pump heads (several thousand PSI) are made from it. Its glass transition temp is only 140C or so, though, which might cause some issues with long term stability in really hot amp conditions. Plastics tend to do funny things over many heat/cool cycles at higher temps. It's not cheap either...
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Tom, do you have a source for the "socks"? It seems like they'd be very handy to ensure that the elevated chips cannot short out in any manner with their surroundings.
Most certainly, I think people were paying $1-1.50 each even when purchased in large quantities 😱
That's cheap. Try $45 for a single 10-32 screw made from Vespel.
Screws made from Ultem are also available.
OK, I just got back the chassis panels from Landfall, anodized black. They look GREAT!
Time to start the assembly and testing process. The plan is to do the filament supply first, then the driver stage, then if all is well the output stage (with most of the really heavy stuff).
But first I need to blacken the stainless steel screws with Caswell SS Blackener. Then the fun can begin!
Time to start the assembly and testing process. The plan is to do the filament supply first, then the driver stage, then if all is well the output stage (with most of the really heavy stuff).
But first I need to blacken the stainless steel screws with Caswell SS Blackener. Then the fun can begin!
I would use a 10A ICL in series with the filament – it'll save some wear-and-tear on your startup circuit.
You can use a 9V relay to bypass it once the voltage across the filament comes up high enough (and therefore, the current, low enough).
Just a thought.
Gotta say, having progressed from 2A3 to Triode-strapped GU-50 to 6C33C to GM-70 SET's, the GU-48 (Russian 833 clone) looks like my next target – after all, it's just a hop skip and a jump from the 1240V HT I used on the GM-70, (but what a jump!)
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Blackened a couple hundred screws today -more than I need for this project but while I had the chem lab cookin' I figured I might as well use it. After a bit of experimenting with a few screws, here's what worked for me:
Caution: 31% HCl can be nasty stuff so wear gloves and ventilate well!
1) Two minute soak in 31% HCl (Muriatic Acid), followed by thorough rinse with distilled water. This step is needed to remove the chromium oxide passivation layer on the surface of the screw. It will not blacken without removing that layer (I tried!).
2) Three minute soak in blackener, full strength, followed by thorough rinse in distilled water.
3) Dry spread out on paper towels. Try not to handle too much as the black does come off if rubbed.
4) Three more minutes in fresh blackener, full strength, followed by thorough rinse in DW.
5) Dry on paper towels. At this point the screws are a dark flat gray color.
6) Spray a few thin coats of clearcoat enamel on the screws heads. The clearcoat darkens the screws to a nice gunmetal gloss black. Not jet black, but black enough, I think.
A little more work than just painting them but hopefully this will be more chip resistant as the black is part of the metal surface. A cool experiment, anyway...
Caution: 31% HCl can be nasty stuff so wear gloves and ventilate well!
1) Two minute soak in 31% HCl (Muriatic Acid), followed by thorough rinse with distilled water. This step is needed to remove the chromium oxide passivation layer on the surface of the screw. It will not blacken without removing that layer (I tried!).
2) Three minute soak in blackener, full strength, followed by thorough rinse in distilled water.
3) Dry spread out on paper towels. Try not to handle too much as the black does come off if rubbed.
4) Three more minutes in fresh blackener, full strength, followed by thorough rinse in DW.
5) Dry on paper towels. At this point the screws are a dark flat gray color.
6) Spray a few thin coats of clearcoat enamel on the screws heads. The clearcoat darkens the screws to a nice gunmetal gloss black. Not jet black, but black enough, I think.
A little more work than just painting them but hopefully this will be more chip resistant as the black is part of the metal surface. A cool experiment, anyway...
Why are you trying to passivate screws? And standard passivation mix for most stainless steels uses nitric acid. 10% in distilled water at room temp. The reason there turning black is your etching them. You removing a layer of metal and leaving a weaker etched surface behind.
Are you going to be running this amp at 400 degrees f in a chlorine gas atmosphere or something? Are you concerned about chrome sensitization? I'm just scratching my head over this. Why are you doing it?
Oh, I see now. This process probably weakens the threads quite a bit. I guarantee they will strip on you pretty ease. Why not just give them a quick paint? Or even send them out for powder coating?
Are you going to be running this amp at 400 degrees f in a chlorine gas atmosphere or something? Are you concerned about chrome sensitization? I'm just scratching my head over this. Why are you doing it?
Oh, I see now. This process probably weakens the threads quite a bit. I guarantee they will strip on you pretty ease. Why not just give them a quick paint? Or even send them out for powder coating?
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Not passivation, blackening. I had to remove the passivation layer.
The guys at Caswell plating said the screws shouldn't be damaged unless I leave them in the solution for hours. Anyway, screws are cheap.
I've done other builds with painted screws and wanted to try something different, plus painted screws tend to chip when they're driven, then I have to touch up, etc. They really are a nice gunmetal black color now; I'll have to see how they look against the anodized aluminum, but I can always spray on a layer of black enamel if I don't like how it looks. Plus I learned a new skill!
I work with hydrochloric acid a lot everyday, hate it. It stinks bad. Fumes like crazy. Muratic is hydrochloric. Hey what ever floats your boat. I was just a little confused at first.
Why didn't you just buy black anodized screws in the first place? They're available at real hardware stores. Locally, I use Tacoma Screw. On-line, McMaster-Carr has just about everything you'd possibly need.
~Tom
~Tom
You can't anodize stainless steel. But you can get black oxide coated bolts. I'm sure screws are available too.