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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 14th May 2021, 12:18 am   #1
Bazz4CQJ
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Default Rusty 2N3055's ?

Steve's thread on PSU's has reminded me that I have an old Kingshill regulated PSU sitting in the garage rated at 24V @25amps. I literally pulled it out of a dustbin, being very pleased when I found that the only thing wrong with it was the internal fuse had blown. It's quite an old beast (1970's?) and I'm sure Kingshill disappeared many moons ago. It uses a British-made transformer (with the mass of a small planet) with numerous tappings and could easily be made to run at anything from 6 to 44V

One thing I should think about it that it uses 12 off 2N3055's as pass transistors, passively cooled. The tops of those transistors are quite rusty and so far, I've done nothing more than squirt WD40 at them.

Does anyone know what happens if rust fully penetrates the top of a 3055? I guess that I should try some very careful sanding to remove the rust and apply some zinc phosphate primer on them, or maybe just clean them with some fine steel wool and apply silicone grease liberally?

B
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Old 14th May 2021, 12:41 am   #2
paulsherwin
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Default Re: Rusty 2N3055's ?

The rust is likely to be cosmetic unless it's really, really bad. You need a lot of corrosion to eat through a power transistor casing. Even if the transistor is penetrated, it won't stop working in typical environmental conditions.

I think steel wool followed by WD40 is a reasonable solution, certainly for hobbyist use.
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Old 14th May 2021, 9:34 am   #3
The Philpott
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Default Re: Rusty 2N3055's ?

Quite hot so..would favour a smear of copper grease. It'll remain there until it gets wiped off. (Obviously you don't want it near the terminals)

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Old 14th May 2021, 9:40 am   #4
barrymagrec
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Default Re: Rusty 2N3055's ?

Fabulous transformers on those old Kingshills, really ooze quality.
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Old 14th May 2021, 10:10 am   #5
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Default Re: Rusty 2N3055's ?

Steel wool then some black paint? The WD40/silicon grease/copaslip is fine functionally but will collect dust and get grungy
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Old 14th May 2021, 11:14 am   #6
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Default Re: Rusty 2N3055's ?

As others have said, it'll take a lot of corrosion to go through the can but if it does do be aware that 2N3055's with the can removed make really quite good photo-transistors! Made a couple of flashgun slaves with them! Sorry, bit off topic there.
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Old 14th May 2021, 10:18 pm   #7
G.Castle
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Default Re: Rusty 2N3055's ?

Sand off corrosion, then coat with air drying electrical varnish works well.
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Old 15th May 2021, 12:31 am   #8
Bazz4CQJ
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Default Re: Rusty 2N3055's ?

I managed to dig my way through the clutter to get within picture-taking distance of the Kingshill, so you can judges for yourselves. The 3055's all seem to have a greasy surfaces, so the WD40 has hung around. I'm sure that originally, the TI markings were visible, but hard to see them in that light. It's a 19" rack unit and has 3 thick aluminium panels each bearing 4 transistors.

I think that someone on the forum said that Kingshill has acquired a good reputation with companies building the huge audio mixing desks used in recording studios back then, but I'm fairly certain that this one never helped record a Beatles or a Stones album .

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