Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: lina on August 14, 2020, 08:32:09 PM
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I see some old threads that ask for/mention chassis plate dxf files, but can't find a conclusive yes or no about the availability of one. I'm considering getting a brass plate laser cut to use instead of the aluminum stock plate. Any chance there's a dxf/etc file I can get for that?
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We don't share our chassis panel CAD files. But it's not that hard to measure a panel and create your own.
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Ah, oh well. To the CAD! ;D
I've also got a dumb question... does the safety ground lug's design do something special, or would it be fine to just solder a lug directly to the chassis' underside? Figure that if I'm gonna design my own plate, I may do away with (or hide) some of the visible screws.
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If you think you can solder well to the brass, then you could certainly do that. If I made a brass plate, I would want to put a clear coat over the whole plate to keep it looking nice, and the effort of soldering to the plate may cook that right off.
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For safety reasons, the safety ground wire should stay connected to the plate under violent accidents that would disconnect other wiring. That's why it has its own terminal and a tight screw holding it in place. Solder connections are nowhere near as strong as screws.
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You could use a screwed on sub-plate below the decorative brass one - four screws, one in every corner. You would still attach some parts directly to the brass plate, connectors for example. That way you can still maintain the original layout and have your clean look. It gets more complicated than a straight up build.
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Solder connections are nowhere near as strong as screws.
I don't know, reworking vintage amps that solder to the chassis is a total PITA. Those are the most difficult connections to remove!
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I know strictly speaking an earth bonding should be a dedicated stud/bolt, however you are going to have to bolt the mains transformer to the chassis anyway, so why not use one of those fixing for the earth bonding?
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I say drill the hole and leave it as designed. One more screw head towards the rear of the chassis isnt going to change the esthetics one bit IMHO. Defeating engineered safety measures is never a good idea either.
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I know strictly speaking an earth bonding should be a dedicated stud/bolt, however you are going to have to bolt the mains transformer to the chassis anyway, so why not use one of those fixing for the earth bonding?
Yeah, I realized that was an option as well, and I'll likely go with that (maybe even solder the lug over the hole just to be extra safe, if I wanna be paranoid about it). Thanks for the responses folks, good things to think about. Just in case I decide to solder to the brass chassis at all, I'll first get a sample plate to test solder strength & see if it burns away lacquer finish in a bad way and whatnot (as Paul B mentioned).
Another question... would it be possible or a bad idea to use a switching jack in place of the power switch? Looking for a switch that fits the design I'm going for but not finding any I'm too thrilled with... figured maybe I could just do that and unplug the headphones to turn the kit "off". If it's not a bad idea to do so, any caveats I should consider?
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I don't think I've seen a switching headphone jack that will switch mains voltage.
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Ah, righto. Figured that was likely the case but thought I might as well ask, thanks.
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Even if such switch exists, do you really want 60Hz mains power a fraction of an inch from your output signal wiring? Seems to me like a recipe for hum. Or if the switch has tons of shielding it will be be huge and very pricey.
cheers, Derek
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True true. Yup, not a good idea even if it was possible. :P
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I know strictly speaking an earth bonding should be a dedicated stud/bolt, however you are going to have to bolt the mains transformer to the chassis anyway, so why not use one of those fixing for the earth bonding?
The separate mounting bold for safety ground is explicitly called out as a requirement in the UL safety rules. These rules are primarily based on actual injuries that have happened in the past, not just things that might theoretically happen.
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I should mention that PJ is completely correct, and my efforts to pull his leg a little on the forum don't always come across as that.
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My advice is to build the kit as delivered in terms of the layout and hardware. We cannot endorse any changes that might be made to the safety aspects that are designed into the kit. Of course I'm not saying you can't do it, I'm just saying it's your responsibility for safety compliance if you do. There's a good reason for a lot of small details in the layout and construction of the kits that builders might never consider.
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Using fancy brass screws shouldn't upset the aesthetic too much.