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Yet another AR-4x rebuild


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My initial post was mistakenly appended to an AR-2ax thread, so at @JKent's suggestion, I have started anew.  I purchased both my 3a's and 4x's at the same time in 1969 and have begun working on the 4x's for "practice" before tackling the 3a's.

So here are some details:  These are original purchase speakers, kept in ideal environmental conditions (but not used for a decade or so) and have the AR-4x name plates and serial numbers (see below) so I'm sure they are 4x's (after assuming they were 2ax's in my original comment, having not done my research OR reading the label on the back.)  ?  I have confirmed from the photos in @Coleman4130's thread "AR4x Crossover Rebuild Check" by @ra.ra(thanks, guys for doing all that work!) that I have the later 2-1/2" tweeters and a single 20 mfd capacitor.  (Can't read the numbers with the induction coil strapped on top, but it has 2 wires.)  This should be consistent with the date.

I have ordered the dope for the cloth surrounds (which look very good) and the 20 mfd capacitor and the 8-ohm 15W L-pads.  I'm a bit puzzled by the 25 ohm resistor.  I do not find any resistor on the crossover board.  My board looks exactly like the photo by @rebelliondog.  Other posts concerning the 4x's are saying no resistor is needed between terminals on the L-Pad for this model.  With my 1969 speakers, is this the case?  Confusing because some of these threads begin crossing over to other models and the trail becomes less clear.  And forgive me for being a total dunce when it comes to electronics.  I'm a chemist -- we don't like sparks.

Cabinets and cloth are in excellent condition and will not receive any amateurish attempts to "fix" what ain't broke.

Serial numbers:
FX250128 and FX246425

I find this a bit curious because the span between the two numbers is very large.  In addition, the FX250128 has the "FX" stamped along with the number, while the FX246425 has a hand-written "FX" before the stamped serial number.  Perhaps a rebuild of a defective original, or just a change in manufacture labeling.  Interesting.  I have not opened the FX246425 up yet so I may find something different in there.

I appreciate any assistance you can give regarding the 25 ohm resistor (or lack thereof.)  I can send photos if necessary.  I cannot read the stamping on the back of the woofer.

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That's roughly the same time I bought my 4x's--exactly 50 years ago yesterday! And like you, mine were the my first restoration project, with help from guys here. Mine are Serial numbers: FX262692 & FX262765. Speakers back then were not sold with consecutive serial numbers. They were sold individually and if you bought 2 at the same time they were probably from roughly the same production run. Yours and mine are the same vintage.

Working on the 4x's first makes sense. They are much simpler (and less expensive) than the 3a's.

Don't bother with the resistor. You can attenuate the output of the tweeter with the L-pad and these old tweets need all the help they can get. A resistor will just tone them down.

I agree--if it ain't broke don't fix it. You can clean the wood with something like Murphy's Oil Soap if you like and use furniture polish or wax.



grill on.jpg

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Another suggested trying to use Deoxit5 to clean the original pots.  I'm skeptical that will work as intended.  I do have a pair of the new L-pads (which I'll save for the AR-3a's) and I don't think I like the idea of taking it down, unsealing the woofer and mucking around again to replace a pair of wonky pots with new L-pads if the old pots don't work.  I think I'll go the the new L-pads with no resistor and see what happens.  Much easier to add a resistor than to R&R the pots.  Also, as a senior citizen, my high frequency hearing is a bit lower than the golden-ear kids who evaluate hifi components.  I'm not playing a lot of new, detailed music, mainly older "golden-era" jazz LPs and CDs along with a bit of streamed stuff of random source.

Surround dope should be here sometime this week along with the 20 mfd capacitors so next week should see them back together.

Thanks for the help!

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On 10/21/2019 at 4:02 PM, MikeD2 said:

...trying to use Deoxit5 to clean the original pots...

Hi MikeD2,

It's a little difficult trying to follow all of your 4x questions in three different threads, but I hope something here might be useful to you. As far as re-furb'ing original pots, it's highly unlikely that only a spritz of Deox will be sufficient treatment to ensure long-term performance, despite its effectiveness at as an electronic parts cleaner. Quite often the metal parts develop extensive corrosion and/or pitting, and this can only be fully confirmed by complete disassembly of the pot, which is a mildly tedious process especially if it then leads into restoration efforts. Still, it is not unusual to achieve properly functioning pots after a thorough cleaning and re-assembly, but this usually depends on the extent of corrosion and the attentiveness of the re-build process.

If the pot re-build idea is not your cup of tea, go ahead and try the new L-pads. (BTW, AR-3a's will take two pairs.) During re-assembly of the speaker, you can conduct your own tests about whether or not to include the resistor, and if you initially decide to leave it off, it can be easily added later directly to the backside of the tweeter without removing the woofer and stuffing.

The re-doping of the woofer is usually not critical for the 4x because the mesh dust cap is intended to allow some passage of air. Nonetheless, I typically apply a light coat of Roy's goop to the 4x surrounds as I feel it helps to re-distribute the original butyl and refresh the suppleness of the cloth fabric.  


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