Fender amp chassis non conducting?

It might be an anodized aluminum skin. Anodized aluminum is very tough...

John :-#)#

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John Robertson wrote: ===================

** Completely wrong colour.

** I am very familiar with anodised Al, this is nothing like it.

..... Phil

Blue tint? That would be your passivated zinc-based material. Yellow tint? That would be *chromated* material. No tint? See Applied Varnish.

Given that the chromated material requires an extra step in the plating pro cess, if this is a passivated plating (which I doubt) I suspect the former rather than the latter. Further, the latter is mostly done for corrosion pr otection, not insulation. Would Fender indulge in a costly process for corr osion protection?

Note that the tints are quite subtle, but definite.

Given that both are rather more costly than a simple applied varnish, of wh ich there are dozens, I would look to one of those rather than something ex otic.

Two of very many.

Now, imagined it being done at an industrial level - the goal would be achi eved at a very low cost.

Note also that anodizing comes in many colors from clear to black and all b etween.

zing/

But of all the options, that is the least likely as it is the most expensiv e. Somehow I do not see a guitar amp manufacturer doing this for something that is very nearly invisible to the end-user.

Peter Wieck Melrose Park, PA

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.

like thousands of others.

gohms between adjacent points on the chassis.

r the back panel. Never seen this before.

nection unreliable.

s 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 t hat 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 fo r protecting the steel from corrosion as we would suspect it would be. He a lso said the plating could be dyed other colors if wanted.

snipped-for-privacy@gmail.com wrote: =======================

ks like thousands of others.

megohms between adjacent points on the chassis.

for the back panel. Never seen this before.

onnection unreliable.

is high resistance.

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 tha t this trivalent chromate finish would also have a bit of sheen to it as we ll, and it most definitely would be resistive in nature. He said it's for p rotecting the steel from corrosion as we would suspect it would be. He also said the plating could be dyed other colors if wanted.

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**   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 labe 
l folded over at the back and held by glue.  
The threads of the various pots and power switch effectively ground it by p 
assing through holes that are free of plating.   

IME whenever such a chassis has a non conducting coating ( eg anodised Al o 
r paint ) makers normally mask off any small areas that need to conduct.  N 
ot the case here. 

I reckon the metal shop simply got batch of plated steel that look normal b 
ut was not correct.  
Nobody with a DMM being around to check it. 


.....    Phil

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

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** Before or after watching this?

..... Phil

Doesn't look like the chassis is used to carry any signal grounding - audio plug has plastic body.

RL

legg wrote: ===========

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** Huh ???

The input jack sleeve is chassis grounded along with the common earth of the PCB.

The majority of guitar amps have plastics input jacks, nearly all Marshall and VOX models for example.

....... Phil

The mounting hardware for that jack is not counted on to make an electrical connection to signal ground.

This was something that you said you were worried about, when considering continuity of the box metalwork.

I think you'll find that PEM inserts have an electrical contact to the metalwork, even though installed after the metal is passivated. If the grounding stud is captive, it likely also benefits from this contact, though star washers are standard for a safety connection there, anyways.

RL

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** Irrelevant. So what if connects another way? ** Where ? I mentioned the speaker jack which is an all metal type. ** Yawnnnn - the holes are made post plating, which I mentioned.

Stop being such a PITA know all.

..... Phil

Holes are usually formed at CNC, before metal bending. Then passivation, then insertion.

To insert before passivation, you'd need either stainless or compatible metal chemistry, unless you permit visible discoloration. Messy.

Which is the more likely Phil com?

'you know, on second thought, there's nothing to worry about, sorry for wasting your time with this.'

or

'I really don't want an answer to this question, so piss off.'

RL

That would be the one.

Peter Wieck Melrose Park, PA