A screw Lose :)

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Rich T

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Hi all, my first post here so ag'day to you all.

I was checking the serial number on my Subway Rocket and noticed this screw loose (no jokes please lol) I removed the chassis and as far as I can tell, there is nowhere for this bolt to attach too. It has a threaded slug it screws into on the main chassis but there is nowhere I can see at the top of the cab or anywhere else to go. I was wondering if it were a spare for the chassis as it is about the same length.

14876433_550863765111006_5456188611956033519_o.jpg


Any ideas?

Thanks

Rich T
 
Talk about an eyesore :shock: That should concern anybody. Hey mesa, can't there be a better way to do whatever that screw does.
 
I assume I'm meant to tighten it up. I can't see any good reason to leave it like that. I'm concerned it could vibrate out.

Rich.
 
Don't over tighten it Rich.
What that screw does, is connect the chassis to a strip of tin foil on the underside of the top of the cabinet.
That tin foil completes a faraday cage, keeping the components in the chassis shielded from RF noise.
The foil is easy to puncture. Do the screw up tight enough that it's touching but not piercing the foil
 
Thanks for that, though I had the chassis out today and there is no foil inside the cabinet.

I had the amp on after I put it all back together and there is no hum or extra noise. The amp had new valves and some caps etc replaced recently. It's all working nicely.

Rich
 
That's unusual. It's common practice amongst amp builders. All my Marshalls and my Mark V have a foil or metal plate that the open side of the chassis makes contact with. As did the plethora of friends amps I've worked on.
Is it the original cabinet?
 
Yes it is, it's a 1995 Subway Rocket. Maybe they didn't do it for that model or back then ?

Cheers

Rich
 
The main purpose of that screw is to put a very slight tension on the chassis to prevent vibrations and rattles. The secondary attribute (more of a lucky result) is better continuity between chassis and foil shield.

I have only seen that screw on long chassis' that hang from the headshell. My Roadster head does not have it, but I believe all the Roadster combos do.

Don't tighten the crap out of it, screw it in with your fingers until it touches the inside of the headshell, then give it about a 1/4-1/3 turn more.

Dom
 
Thanks for that Dom. Yes that's what I have done, I finger tightened it with a tight pinch. Now screwdriver.

I'll leave it like that.

Cheers

Rich
 

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