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Post subject: My AB763 Silverface SR project - and a question
Posted: Wed Oct 05, 2011 6:52 am
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Hi All,

A few months ago I posted abotu my sliverface Super Reverb project. As a result of a bunch of help, I am finding great (but slow, due to lack of time) progress.

But last night I started a resistor replacement exercise that came from a discussion I had with Arjay and getting bias levels set right to try and fix a dirty sound.

So I was relacing the 220Ks that link the power tubes to the bias circuit. And when holding one with pliers during removal, it broke. And did another one, and it broke. So did a few more and the break rate was over 50%. Now I did not think I was applying too much pressure, but I became acutely aware that age and heat seem to have done a number on many of the passive components in such a vintage amp.

So are my findings normal? Are fragile resistors after 40+ years a common occurence? Surely if they are so fragile, they also cannot necessarily be doing the job as designed?

Or did I just pull them too hard when removing and am thinking too much?

Chris


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Post subject: Re: My AB763 Silverface SR project - and a question
Posted: Thu Oct 06, 2011 5:01 pm
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Joined: Sat Jul 03, 2010 2:18 pm
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Ok... this is what I do to hold a resistor or cap while soldering. Use a SMALL alligator clip in the center of the component (this also helps to dissipate heat, so that you do fry the component---esp caps). Be sure that the component fits the hole and is the leads are already cut and bent to final shape.

OR use a small rubber band and wrap in around the needle nose plier's tip---just enough to hold the component, but not crush it. I put masking tape on the tip of the pliers---so as not to ruin the markings on the component.

Clean the surface to be soldered. 91% Isopropanol is fine. Let DRY. Get the heat up and running on the iron, first. Test it on a dummy solder point. You should only need to touch the solder point a few seconds to get a good flow. Use good solder. I like Kester 60/40. And I like a small FLAT tip on the iron. Weller, Hakko make good brand irons. They should have heat adjustment knob.

Good luck with that! Experiment first, before actaully soldering in the real piece. It'll help you get the heat correct, as well as your technique. I like Luxo Lamps with magnifying lens to helps "get thing right."

http://www.ebay.com/itm/Luxo-16353LG-Li ... 3cbcd46392


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Post subject: Re: My AB763 Silverface SR project - and a question
Posted: Thu Oct 06, 2011 5:41 pm
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Thanks BMW,

I have done a great deal of soldering in the past, but always good to hear reinforcement of good practice.

In may case, since I was replacing, I applied slight pressure to outgoing resistors -that was when I experienced the breakage - I have never experienced such brittle components before. I was just so surprised.


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Post subject: Re: My AB763 Silverface SR project - and a question
Posted: Thu Oct 06, 2011 6:17 pm
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Joined: Wed Mar 31, 2010 12:48 am
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Location: Tombstone Territory
I always disconnect components one lead at a time, and I remove the parts by using the first detached lead as a purchase point. Old resistors, caps, and bakelite tube sockets do become brittle with age and it's best to treat them as gently as possible.

HTH

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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