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Thread: 'That look' - metal finish

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    Senior Member BCNZ's Avatar
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    Default 'That look' - metal finish

    This is more an engineering question.

    Some of you will know the Perreaux products that were made here in NZ in the 80s - big heavy power amps, 1U rack mount preamplifiers and so on.

    What I'd like to know is what process they used to get that smooth but 'rough' look on the front panels. It almost looks like the aluminium has been bead blasted using very fine beads.

    I know it's not sandblasted as I did try that on a piece of extrusion once and it was sort of the same finish, but the sand was obviously too coarse and caused too much pitting of the metal leaving the surface too rough.

    I did send an email to one of the original owners of the company who was around at the time these things were made, but he couldn't remember.
    I know there are other equipment manufacturers who use a similar finish on their gear.



Look Here ->
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    your not thinking of a "2 pack" finish are you
    When I explained to the guy what avatar I wanted, that wasn't what I meant!

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    Junior Member TZB's Avatar
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    Sounds like "Hammer finish". I think you can buy it in a spray can.

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    Quote Originally Posted by Studio1 View Post
    What I'd like to know is what process they used to get that smooth but 'rough' look on the front panels. It almost looks like the aluminium has been bead blasted using very fine beads.
    No idea what the perraux finish was like, but something matching your description could be done by etching an aluminuim front panel in caustic soda (sodium hydroxide) and then sealing it a clear polyurethane varnish.

    It requires a lot of trials to get it right, leave it too long and your panel gets eaten away!

    Found some instructions on the net....

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    the newer stuff looks like this



    and they explain it all here



    not sure of the older gear though

    regards...

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    Member PunX0r's Avatar
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    Yeah TZB, you sould like you are on the mark, we used it on our workbenches in here and it is like what Studio is describing.

    We used a brand called Hammertone

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    Actually looking at it appears to be more of a Granite look than a Hammertone. Though Hammertone was used a lot on older gear.

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    Ok, it's not hammertone, it's not a hammer finish (have used that in spray cans for other applications so I know what it's like), it's not the finish like the recent Perreaux stuff (as in the Norwegian report above) and it's not 2 pack.

    All good guesses tho!

    SSrattus - I think you might be on the right path. In an old Perreaux brochure (that I have stored away in my lockup) I remember seeing 'dipping baths' and them describing how the aluminium panels had to be 'processed' - the subsequent photos (Black and white) showed aluminium cabinet parts such as rack handles and panels hanging on wires, suspended in these baths.
    This would equate to them being dipped in caustic soda solution. I think I will need to get the old panel (it's in storage as well) and post some photos here. Then I might need to do some 'testing'.

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    Dipping in caustic soda is basic home method of doing it, a manufacturer could dip in other chemicals as well to achieve different grades of finish. Or they could be anodising the aluminium, it is a much harder finish.

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    Junior Member expitaxial's Avatar
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    Speaking of kiwi amps with brushed aluminimum has anyone got a schematic for a ZPE 1000?

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    Quote Originally Posted by expitaxial View Post
    Speaking of kiwi amps with brushed aluminimum has anyone got a schematic for a ZPE 1000?
    I have some contacts here who may be able to help. I'll fire some emails off and let you know what comes back.

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    Junior Member expitaxial's Avatar
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    Default zpe1k

    Hi Studio1, Thanks and there is NO hurry.. Intrestingly the fault is in the front end rather than the output stage. Its one of them 'I will get around to it one day jobs' cheers Craig

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    Yup, that's usually where the faults are in high power amps. Rarely have I seen the output stage killed in one - as they are pretty bullet proof - they have to be when you're dealing with 50+ volts and in excess of 20 A continuous current!

    I've tracked down the company that apparently has information on these amps.
    I will call them on Monday if I get a chance.

    ZPE [Zetka Power Engineering] goes back to the 80s I believe. They haven't been around for some time.

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    Junior Member expitaxial's Avatar
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    Ta, It had a bit of a failure some years back where the smoke escaped but I patched it up ok (good to have the other ch in one piece for ref) Yep its an old beast now. The rails are at least +/-80V. I prey for outputs to stay semiconducting as they are hard to find (the old hitachi lateral mosfets)
    here is a photo damaged area circled I recall I had to replace a dead o/p fet.
    Cheers Craig

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    Ok, that looks like the driver section for the outputs. If an output FET goes S/C it will generally take out the drivers in this area as well - and catastrophically as it has already done.
    I don't think the circuit will be too different from the Perreaux design of similar power. They did a 1 kW amp but I don't remember the model number.

    The Hitachi pairs (2SJ49 / 2SK134) were a well used configuration and the circuit design to drive them is pretty standard.
    Hitachi also did the slightly lower rated 2SJ48 / 2SK133 pair, and the higher rated 2SJ50 / 2SK135.
    Believe it or not, these devices are still available. I have a couple of component drawers full of NOS. I think mine are the 2SJ48 / 2SK133 types tho. I bought a heap of them in the 80s when I was building mosfet amps.

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