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Post subject: Re: Crackly hum after Showman SF AB763 restoration
Posted: Fri May 06, 2016 8:26 am
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Old jacks have three common issues. Corrosion, alignment, and loose swedge.
The first thing to look at is down the barrel to eyeball the tip contact.
If it has black crud on it, Q-tip and alcohol. Now look closely at the clean spot where the tip touches the tang. If it is shiny silver, thats good. If it's coppery colored, the plating is worn away and the copper easily corrodes in a short time. Replace the jack.
If the barrel is corroded, a fine sandpaper around a Q-tip can burnish it.

Looking down the barrel, the tang should protrude about 1/3 of the way into the barrel diameter.
If the shorting switch does not have good pressure against the tang, it can be bent at its base to increase the pressure. If you can't access the base, the tang can be bent out of the way to get access to bend the switch contact. Rebend the tang and realign. As with most metals, overbend a bit and bend back into proper position.
Inspect both switch contact points for pitting and corrosion. A pitted surface can be cleaned, but will never stay that way.. It will pop and hum. Replace the jack. There is no spray that can replace good nickel plated metal for a low resistance contact.

The metal of the barrel is bent over, or swedged, to fasten it to the ground lug. If the jack is overtightened, it can pull this swedging loose.
The result is a nut that won't tighten. It just spins. If you pull the jack and use a file through the plating, you can solder it together, but otherwise, replace it.


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Post subject: Re: Crackly hum after Showman SF AB763 restoration
Posted: Fri May 06, 2016 10:37 am
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Joined: Wed Mar 31, 2010 12:48 am
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Location: Tombstone Territory
TimsAudio wrote:
If the barrel is corroded, a fine sandpaper around a Q-tip can burnish it.


Crokus cloth (used by gunsmiths) is a better material for this purpose.

https://en.wikipedia.org/wiki/Crocus_cloth

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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