Delicate soldering

[ra.ra]

Shortsighted on their part perhaps, but I will acknowledge that Acoustic Research did make a conscious attempt to instruct consumers to refrain from fiddling around with the sealed speaker construction of the classic AR's, as evidenced by the statement found on every rear s/n paper tag:

"No attempt should be made to open cabinet ......... blah, blah ......"

That may be the rationale for the original designers having confidence in all of the delicate wiring left semi-exposed (usually underneath black electrical tape) behind the linen grilles, instead of safely tucking it all inside the solid cabinet. Still, while I will not claim to understand the particular factors involved (from an electrical engineering standpoint) in the specific design of the many high and mid-range drivers where this occurs (AR-2, 3, 4, 5, 6, 7 and 8 series), this vulnerable wiring has always struck me as a very weak point in the industrial design of these otherwise excellent products. OK, that's my rant .... now on to my problem.

I recently purchased a couple of tweets which were original to the AR-18B (p/n 200034-0, mfr. date '83) and even tho' these have the protective screen, somewhere during transit between salesperson and purchaser, it appears that one of these delicate leads has become "unattached".

So my question is how to fix? I am certainly not the best electrical technician (e.g solderer), but I would really appreciate advice on how best to re-connect this wire to the external terminal. Also, is there a glue or other substance suitable to adhere these tiny wires to the cone and/or tweeter frame? What did AR use in original manufacturing? What is all that yellow adhesive?

[xmas111]

Hi Rob,

I would try and get some solder on the terminal first then very gently solder the wire to it. Then either put a dab of glue or a small piece of electrical tape over the whole terminal.

Sure others will have better methods.

Good luck with it.

John

[redpackman]

The key is a small, but adequate amount of flux. Flux on both surfaces enables the solder to adhere to both surfaces and then weld them together, completing the circuit.

Put flux on both surfaces, just a small amount, just enough to be seen, NOT a glob. That's overkill. Then put another small amount on the tip of your hot soldering iron and then "tin" the end of the iron by bringing the hot, now "fluxed" tip of the iron in contact with some solder from your supply. Again, just the smallest amount of solder is needed, not a whole glob. Then with the tip of the hot iron tinned with solder and hot flux bring it in contact with the two fluxed target points that you have brought into contact with each other. Aided by the flux, the solder will flow onto the wire and terminal and form a circuit. Remove the hot iron and hope that the wire and terminal stay in contact as the solder cools in the next seconds. IF and when it does you'll likely have a completed circuit and be in business.

Here's an example of a similar and very delicate repair I was lucky enough to succeed in. I couldn't even see the wire protruding from the tweeter cone, but the flux and solder found it and made a circuit. The tweet is still working!

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7953

I don't know about every variety of glue available, but I'd apply tape only after the solder circuit has been established. The tape then acts as a "support" or a brace for the wire and circuit. I'd avoid glue. If you ever have to repair it again, tape can be removed but glue would just muck things up for another re-soldering attempt.

[RoyC]

I've done quite a few delicate soldering jobs on these and other tweeters, and have never had to use outboard flux. Solder such as Kester "44' rosin core (.031 inch) will work very well with a fine point soldering iron tip.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=370-074

Be aware that the voice coil wire has a coating on it. It appears in the photo there is still a solder covered area at the end of the lead, which should make it easier to re-solder.

A thin application of any glue (ie white pva/tacky glue, etc) will work fine...just be careful not get too much glue on the cone.

Roy

[ra.ra]

Thanks to all of you for the advice - there are helpful tips in each of these responses. I have not performed any work yet, but intend to get around to it sometime soon.

Roy's keen observation that the damaged wire still has some solder appears correct - - I have looked again with a magnifier to confirm this. And since I need new solder anyway, his recommendation is timely as well, but I am curious about this: exactly what are the performance differences between solder that is 60/40 and solder that is 63/37? Regarding the notion of added flux (or not), it seems that the idea is to create an environment that facilitates an easy and ample flow of connective metal alloy, and from what I can tell, it appears this particular Kester solder touts that particular attribute. Still, I often use a cheap little 25W Radio Shack soldering iron, and have no idea what the necessary temperature requirements may be.

If I am able to successfully make the 'fix' on this tweeter, I have another similar tweet afflicted with a similar disease, so I may be able to kill two birds here with one stone, so to speak. As a point of interest, here is a distributor (near me) that sells this item at a substantially lower cost that P/E (see attached images as well).

http://www.hmcelectronics.com/product/Kester-Solder/SN63314466

Last question, a bit off topic maybe - - - can someone remind me what gauge of colored wire was used inside the cabinets during the classic era of AR speakers? I think I remember someone stating that it was 18 ga., but I know some restorers like to use a heavier gauge for the woofers.

[RoyC]

ra.ra,

For our purposes it really doesn't matter which flavor you choose. I've been using 63/37 for years. Your 25 watt iron should work fine.

The AR crossover wires were mostly 20ga and 18ga. There is absolutely no reason to go with anything heavier than 18ga inside the cabinet unless someone has given you a free roll of something else.

Roy

[ra.ra]

Great advice as always, Roy.

Thanks.