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AR3a re-build (capacitors)


Guest Nigel

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Guest Nigel

>Should I replace it?

You could if you want to using "high grade audio"

see: http://welbornelabs.com/hov.htm

>If not how can I test

>it ? (or should it

>be OK)

Radio Shack or similar have capacitance testers/meters.

>I remember from the inside of

>the other set there were

>2 cans (capacitors) screwed to

>the bottom.

>

>Just what's in that box ?

2 capacitors

>In order to read the box

>I cleaned it so if

>it goes back what can

>I use for a replace

>of the anti-electrolytic substance.

Go to a place like US Harbor Freight Tools, or similar, they have a plastic/rubber coating that is put on drills and milling machine cutters after sharpening. Small items can be dipped, larger items can be "painted". It ends up around 1/16" thick.

Nigel

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I purchased a 2nd set of AR3a's and while using one set, I plan to go thru the new set more thoroughly than the first. Questions for the gurus:

On the back of the inside about 1/4" from the bottom and centerd, there is a box being held on by 3 metal straps. Its marked 50mfd 50VDC & 150 MFD 50 VDC. There was some tar paper looking material (stops rusting ? ) under the straps.

Should I replace it?

If not how can I test it ? (or should it be OK)

I remember from the inside of the other set there were 2 cans (capacitors) screwed to the bottom.

Just what's in that box ?

Is a dual capacitance capacitor ?

In order to read the box I cleaned it so if it goes back what can I use for a replace of the anti-electrolytic substance.

Thank in advance for any help.

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  • 5 months later...

I (stan461) posted this some time ago. I want to thank Carl for responding and I will defintely proceed with his recommendation. Here is his response in an EMail to me:

*****************************************************************

Did you get the help you needed? Those caps are very old technology. They should be replaced with more modern, non-polar electrylytics. The 150 mf is for the woofer and can be replaced with an inexpensive one. The 50 mf and the 6 mf should have a metallized polypropelyne replacement. Lane Audio in Nashville, TN sells the caps. Or you can go to Madisound.

Unscrew those straps and cut the wires at the edge of the cap body and remove the huge clunker and junk it.

Carl, The Speakerdoctor

*****************************************************************

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  • 13 years later...

14 years later I'm restoring another pair of AR3a speakers.

This time I purchased a capacitor tester.

First I checked some new caps just to verify.

Works like a charm!

Next I yanked the caps out one 1 of the speakers and here are the results:

6mfd now measures 9mfd.

50mfd is now 84mfd and the 150mfd measures 219mfd.

I'll measure the other caps in the other AR3a before I toss them.

I expected them to be off, but not as much as they are.

I never heard this particular pair due to the pots being inoperative so I'm

left wondering what the difference in sound will be.

Anyway, it's too late and I'll be ordering from Madisound shortly.

I'm going with the Carli MET 6.0 mfd Non-Polar Mylar Capacitor 150V, the Bennic NPE 150uf and 5 surplus 10uf for the mids.

P.S. just measured the other one:

6mfd now measures 9.49mfd.

50mfd is now 107mfd and the 150mfd measures 304mfd.

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Not replacing the pots. Yet.

The pots cleaned-up really nice and I'm finishing off the job by applying some dielectric grease.

Also, I'm replacing the wool that was in there with acousta-stuf.

I used a filtration mask when removing the wool which was spewing particles into the air (like you wouldn't believe) as I gently pulled the pieces out of the cabinet.

After that, vacuuming and then wiping the inside of the box with a damp paper towel.

I detest fiberglass, thus the Acousta-stuf.

If I have to start playing with the pots down the road, then it's back into the boxes to replace them all with LPads.

It's a hobby and yes... it is fun.

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This time I purchased a capacitor tester.

First I checked some new caps just to verify.

Works like a charm!

Next I yanked the caps out one 1 of the speakers and here are the results:

6mfd now measures 9mfd.

50mfd is now 84mfd and the 150mfd measures 219mfd.

It looks like it was time to rebuild.

Limitations of LCR meters when measuring NPE´s was discussed some time ago and it was found out that measurements will differ less than 10% compared to bridge measurements. Your findings are quite similar to what I have found when measuring 40 year old electrolytic´s. They always seems to measure 50-80% more than specified. I have thought that manufacturing techniques were reason for this, as tolerance specs for electrolytic´s were usually something like -20% to +50%. Recently I have thought that if it is possible that drying electrolyte will force capacitor plates closer to each other and this is actually the reason for increased capacity of old electrolytic´s.

Any other idea or suggestions?

Best Regards

Kimmo

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