- Fender amp chassis non conducting? - 6 Updates
| whit3rd <whit3rd@gmail.com>: Jun 25 11:44AM -0700 > To get a ground connection you must use one of the threaded bolt holes for the back panel. Never seen this before. > Surely this makes grounds on speaker jacks and even the safety ground connection unreliable. > I have read that the plating may be " chromated zinc passivated " which is high resistance. To get through paint or plating, a star-type lockwasher is good; screw/lug/lockwasher/chassis is a reliable grounding connection, even if you replace 'screw' with 'rivet'. Loctite screw thread application doesn't seem to hurt the grounding with a machine screw, either. |
| "ohg...@gmail.com" <ohger1s@gmail.com>: Jun 25 03:44PM -0700 > I have read that the plating may be " chromated zinc passivated " which is high resistance. > Any ideas? > ..... Phil I called my brother who is a research chemist. He said it could very well be the chromated zinc passivated finish you suspect. He said the steel is first zinc plated, then a trivalent chromate finish is applied over it. If it's colorless or slightly blue, that's probably what it is. He did say that this trivalent chromate finish would also have a bit of sheen to it as well, and it most definitely would be resistive in nature. He said it's for protecting the steel from corrosion as we would suspect it would be. He also said the plating could be dyed other colors if wanted. |
| Phil Allison <pallison49@gmail.com>: Jun 25 04:10PM -0700 ohg...@gmail.com wrote: ======================= > > Surely this makes grounds on speaker jacks and even the safety ground connection unreliable. > > I have read that the plating may be " chromated zinc passivated " which is high resistance. > I called my brother who is a research chemist. He said it could very well be the chromated zinc passivated finish you suspect. He said the steel is first zinc plated, then a trivalent chromate finish is applied over it. If it's colorless or slightly blue, that's probably what it is. He did say that this trivalent chromate finish would also have a bit of sheen to it as well, and it most definitely would be resistive in nature. He said it's for protecting the steel from corrosion as we would suspect it would be. He also said the plating could be dyed other colors if wanted. ------------------------------------------------------------------------------ ** Thanks for that. Here are some pics showing the chassis details of one: https://www.mojotone.com/blog/fif-blues-junior-power-transformer-swap Look *exactly* like ordinary zinc plated. FYI: The top, where the controls knobs are, has a thin, nickel plated steel label folded over at the back and held by glue. The threads of the various pots and power switch effectively ground it by passing through holes that are free of plating. IME whenever such a chassis has a non conducting coating ( eg anodised Al or paint ) makers normally mask off any small areas that need to conduct. Not the case here. I reckon the metal shop simply got batch of plated steel that look normal but was not correct. Nobody with a DMM being around to check it. ..... Phil |
| Clifford Heath <no.spam@please.net>: Jun 26 12:16PM +1000 >> ..... Phil > I called my brother who is a research chemist. He said it could very well be the chromated zinc passivated finish you suspect. He said the steel is first zinc plated, then a trivalent chromate finish is applied over it. If it's colorless or slightly blue, that's probably what it is. He did say that this trivalent chromate finish would also have a bit of sheen to it as well, and it most definitely would be resistive in nature. He said it's for protecting the steel from corrosion as we would suspect it would be. He also said the plating could be dyed other colors if wanted. Thank for the response. To satisfy my curiosity, can you ask your brother what process and chemicals are used to add the trivalent chromate finish? Yes, I realise that chromates are dangerous, hexavalent chromium is a carcinogen. Ch |
| Phil Allison <pallison49@gmail.com>: Jun 25 08:42PM -0700 Clifford Heath wrote: ------------------------------ > Yes, I realise that chromates are dangerous, hexavalent chromium is a > carcinogen. ** Before or after watching this? https://www.youtube.com/watch?v=BGX4nMrnxg0 ..... Phil |
| legg <legg@nospam.magma.ca>: Jun 26 09:13AM -0400 On Fri, 25 Jun 2021 16:10:09 -0700 (PDT), Phil Allison >I reckon the metal shop simply got batch of plated steel that look normal but was not correct. >Nobody with a DMM being around to check it. >..... Phil Doesn't look like the chassis is used to carry any signal grounding - audio plug has plastic body. RL |
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