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Old 17th Sep 2017, 1:18 pm   #1
GW4FRX
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Default Radford amplifier chassis refinishing?

Not being at all well versed in the art of metalwork, Iíd greatly value the wisdom of the forum in respect of the chassis of a Radford amplifier currently under restoration.

It seems to be steel judging by its weight although itís been plated or passivated. Thereís rather a lot of staining and discolouration and also what appears to be pitting. Viewed through an 8x loupe the latter looks almost like tiny rust spots. My best guess is that something has been spilt inside the amp at some stage. Hopefully the photos give some idea of the problem.

None of the stains respond to any solvent on my shelf including AVGAS (which can be very effective on metal staining) and common household cleaners donít touch it either. It would seem that the only solution is going to be refinishing of some sort but can anyone suggest the best way to go about it? A colleague recommended powder coating but this isnít something Iím familiar with.

Any advice very gratefully received and I'll happily send more detailed pics if it helps.
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Old 17th Sep 2017, 1:46 pm   #2
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Default Re: Radford amplifier chassis refinishing?

Some of the steel treatments of the period you won't be able to get redone, like passivated cadmium plating which was quite common

There seems to have been some sort of corrosion which you want to be sure is gone before adding any coating. So I think I'd start with bead-blasting to get to clean metal.
You could go for painting them yourself, starting with a steel compatible primer.
You could send them off for nickel or chrome plating
You probably have a powder coater near you.Done properly, powder coating comes out like a durable but softish paint. Some powder coating comes out almost like dipping in PVC.

If it was metal finish before, I'd probably go for nickel plating. A recent thread mentioned a firm in Manchester doing anodising (for aluminium) who may be worth asking. You may want a conductive treatment rather than powder coat or paint from the point of view of screening.

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Old 17th Sep 2017, 2:49 pm   #3
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Default Re: Radford amplifier chassis refinishing?

It's hard to tell from the pictures just what the original finish was and, as Wrangler says, it may well be some obsolete process. Powder coating involves firing tiny plastic particles from a gun on the surface and then cooking at ~200'C. Tends to produce a layer thay could be mistaken for thick paint. OK for garden machinery, perhaps even modern radio equipment, but suspect it will not look right on vintage equipment.

Maybe the way to go would be a zinc plater who can tint his plate.

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Old 17th Sep 2017, 3:27 pm   #4
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Default Re: Radford amplifier chassis refinishing?

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Originally Posted by Bazz4CQJ View Post
It's hard to tell from the pictures just what the original finish was and, as Wrangler says, it may well be some obsolete process.
It's definitely not cadmium-passivated -- the colour is wrong -- and it's a rather odd finish. In certain lights or from certain angles it almost looks grainy and under the fingertips it feels slightly rough. I've asked on the Radford forum since it's just possible that someone on there worked on the original.

From what's been said so far it doesn't sound as though powder coating would be a good move. The thread about re-anodising heatsinks was mine (it's the same amplifier) and I'll ask whether they can also do bead-blasting and plating.
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Old 17th Sep 2017, 5:37 pm   #5
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Default Re: Radford amplifier chassis refinishing?

Radford Revival might know - http://www.radfordrevival.co.uk/ - they are very helpful chaps.
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Old 17th Sep 2017, 5:58 pm   #6
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Default Re: Radford amplifier chassis refinishing?

Powder-coating could be problematic: the resultant coating is insulating so you'd need to scrape the coating away anywhere there's a need for a bolt-through earth tag.

I'd get it bead-blasted as a first approach, then perhaps an acid-pickle (chromate) to clean out any deep-seated pitting.

Then a very-fine misting with etch-primer [you still want to be able to see the underlying metal through the misting]. These guys: http://www.arc-rite.co.uk/aluminium-...y-sizes-1564-p are worth consulting.

Then spray the topside of the chassis with whatever topcoat colour floats your boat, but leave the underside unpainted for better contact where you need to bolt-down tags/valve-bases etc.
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Old 18th Sep 2017, 5:53 pm   #7
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Default Re: Radford amplifier chassis refinishing?

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Originally Posted by RojDW48 View Post
Radford Revival might know - http://www.radfordrevival.co.uk/ - they are very helpful chaps.
Thanks for that -- I did so and they tell me that Radford chassis of that era were most likely zinc-plated. So now it's probably a matter of finding a bead-blaster and plater.

Must say it's very tempting to get it chrome-plated
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Old 18th Sep 2017, 8:19 pm   #8
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Default Re: Radford amplifier chassis refinishing?

Zinc takes time to age and settle to the point where anything will stick to it. Chrome shows every blemish. A matt Nickel finish may be preferable.

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Old 19th Sep 2017, 3:17 pm   #9
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Default Re: Radford amplifier chassis refinishing?

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Zinc takes time to age and settle to the point where anything will stick to it. Chrome shows every blemish. A matt Nickel finish may be preferable.
I've now e-mailed six plating firms asking whether they could bead-blast and plate a steel chassis 290 x 260mm. Five declined saying they were too busy, couldn't undertake such work, etc, etc. The sixth wanted £385 plus VAT!

Does anyone know of a company who could do this work without it requiring a second mortgage?
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Old 19th Sep 2017, 4:43 pm   #10
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Default Re: Radford amplifier chassis refinishing?

There's a fair bit of information on the Web about DIY Zn plating. Might be worth reviewing.
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Old 19th Sep 2017, 4:55 pm   #11
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Default Re: Radford amplifier chassis refinishing?

I've not used any for years, but if you Google "vintage motorcycle plating" you should find plenty of companies active in re-plating vintage m'cycle parts (e.g., frequently small order quantities & sizes). It might be worth calling a couple. £385+ certainly seems outrageous / just a price from someone not wanting the job.
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