AR-2AX smoked pots & Tweeter dome???

[Tom H.]

Hi everyone.

We are just starting out with restoring a pair of AR-2AX speakers. We got them apart today and have a couple of questions.

At some point the pots and nearby wiring got very hot. The pots are disintegrated and the wires are burnt nearby. What caused this? Was it excessively loud music for a long time? Visibly the dual capacitor and inductor look OK. I had planned on replacing the crossover and pots anyway. I knew they were toast. One of the speakers got so hot the holes where they mounted literally got burned to the point where they wouldn’t hold the pots anymore.

Is the dome of the tweeter supposed to be pliable or move slightly when you touch it? It seems hard as a rock. I have not ohmed out the drivers yet.

The woofers look OK except for the foam of course. I don’t think these cabinets have ever been opened as we had to fight to get the grills off, woofers out and the everyting else looks original.

Thanks for anything. This will be the first in a long line of questions I’m sure.

[dynaco_dan]

Hi everyone.

At some point the pots and nearby wiring got very hot. The pots are disintegrated and the wires are burnt nearby. What caused this? Was it excessively loud music for a long time? Visibly the dual capacitor and inductor look OK. I had planned on replacing the crossover and pots anyway. I knew they were toast. One of the speakers got so hot the holes where they mounted literally got burned to the point where they wouldn’t hold the pots anymore.

Is the dome of the tweeter supposed to be pliable or move slightly when you touch it? It seems hard as a rock. I have not ohmed out the drivers yet.

The woofers look OK except for the foam of course. I don’t think these cabinets have ever been opened as we had to fight to get the grills off, woofers out and the everyting else looks original.

Thanks for anything. This will be the first in a long line of questions I’m sure.

Hi there

Thank you for your commentary on how much damage was done to the pots and surrounding area.

The damage might not have been so severe if the speakers had been fused.

Perhaps fusing them may be an option after your restoration.

Please do not touch the tweeter dome as you can most certainly damage it, beyond repair.

They are not available brand new, but are available on the used circuit.

There is look-a-likes and sound-a-likes, but no actual original equivalent drivers made today.

There is alternate brand drivers that have been adapted as near suitable compromises.

I would check out the drivers before going too far, with the severe pot damage, they may be also wounded.

In particular, an individual isolated driver can be tested with a small 1 1/2 volt battery, no larger.

Be sure to use a capactor on the mid and tweeter and use very low volume, for amplier testing.

Testing a mid without a capacitor inline may cause permanent damage, especially the tweeter.

This is if you are using your amplifier to test them.

Any chance of HD photos of the damage?

They may be the earliest 4 1/2 watt pots, rather than the later, A-P 25 watt pots.

[Tom H.]

I have 6 to 6.5 ohms on both mid ranges and one tweeter. We removed the bad tweeter. I don't know if there were breaks in the fine wiring that goes to the front of the driver but there are now. I could not get any reading on what remains of the wire so it appears that one tweeter is toast.

I think tomorrow I may build a temporary crossiver for the purpose of testing the drivers and see if they are OK sonically. I will also battery test the woofers. Both have resistance. I don't remember what it was but seemed reasonable.

Thanks, Tom

PS The date code on the one tweeter we removed was 1970. I don't know which version of pot I would have had. I'll try to get pictures of the carnage tomorrow.

[dynaco_dan]

I have 6 to 6.5 ohms on both mid ranges and one tweeter. We removed the bad tweeter. I don't know if there were breaks in the fine wiring that goes to the front of the driver but there are now. I could not get any reading on what remains of the wire so it appears that one tweeter is toast.

I think tomorrow I may build a temporary crossiver for the purpose of testing the drivers and see if they are OK sonically. I will also battery test the woofers. Both have resistance. I don't remember what it was but seemed reasonable.

Thanks, Tom

PS The date code on the one tweeter we removed was 1970. I don't know which version of pot I would have had. I'll try to get pictures of the carnage tomorrow.

Hi again Tom

As far as a temporary crossover is concerned, the woofer needs no filtering, the mid needs a cap to filter out the bass and the tweeter needs a cap also to filter everything below it's

crossover frequency.

This is for testing each driver individually.

Photos would be a great teaching tool, thank you.

[Tom H.]

Dan et All.

Here are some pictures of the carnage. I'm suprised the speakers didn't go up in flames. I never believed that you could start a fire with loudspeakers until now. Is there any way to tell if these are the lower wattage type pot that was mentioned?

We are going to do some audible testing of the drivers later today.

Thanks, Tom

[RoyC]

Dan et All.

Here are some pictures of the carnage. I'm suprised the speakers didn't go up in flames. I never believed that you could start a fire with loudspeakers until now. Is there any way to tell if these are the lower wattage type pot that was mentioned?

We are going to do some audible testing of the drivers later today.

Thanks, Tom

Tom,

Your 2ax speakers will have been equipped with the typical, troublesome 15ohm/25watt Pollak pots. I have seen this before. Resistance increases with corrosion, causing a corresponding increase in heat. If an original pot (or even a common 15W modern l-pad) is working properly that kind of heat will not occur during normal use. The first AR-2ax's I worked on (in 1980) were less than 8 years old. The problem was corroded pots.

Roy

[JKent]

Hi Tom

Here's a suggestion: Go to PartsExpress and order 4 L-Pads, 2 25 0hm resistors, 2 Hi-Vi tweeters and 2 .05mH inductors. Oh--and new film caps: 2 each 4uF and 6uF. Rebuild your 2ax's with the L-pads and HiVi tweeters (resistors for the mids). They will be very durable and sound great. You can sell the one good tweeter here in the For Sale section. Here's the shopping list:

• (4) L-Pad 15W Mono 3/8" Shaft 8 Ohm
• (2) 25 Ohm 10W Precision Audio Grade Resistor (or a plain 10 watt resistor is probably fine)
• (2) HiVi Q1R 1-1/8" Textile Dome Tweeter
• (2) 0.05mH 18 AWG Air Core Inductor
• (2) Dayton Audio DMPC-4.0 4.0uF 250V Polypropylene Capacitor
• (2) Dayton Audio DMPC-6.2 6.2uF 250V Polypropylene Capacitor

I use L-pads in my AR 4x and 2ax speakers and they work great. Recently put HiVi tweeters in my AR 3a's and can recommend them highly. Roy has done a lot of work on the L-pad and HiVi tweeter mods, including figuring out what resistor and what inductor to use to give them the most authentic sound. His labors have paid off!

Here is a thread with photos of my 2ax crossover with L-pads and film caps, and the mids with 25 ohm resistors. I used newer original 2ax tweeters with black domes on these but in the future would opt for HiVi tweets:

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=4466&st=0&p=76185entry76185

If you insist on original tweeters, you can find another 2ax tweeter, but you've got the tiny lead wires to contend with, plus the fact that the suspension has probably stiffened with age, and sooner or later the domes will "pop" (if you have the original red phenolic dome tweets. Maybe the newer black paper domes, too. They also have the 3-point foam "blob" suspension). Despite their much-heralded dispersion, I don't think the old tweeters are worth the hassles. Of course YMMV

Kent

[dynaco_dan]

Dan et All.

Here are some pictures of the carnage. I'm suprised the speakers didn't go up in flames. I never believed that you could start a fire with loudspeakers until now. Is there any way to tell if these are the lower wattage type pot that was mentioned?

We are going to do some audible testing of the drivers later today.

Thanks, Tom

Hi Tom

Thank you for posting the HD photos.

I am in shock at the sight of that damage.

I have never seen such extreme fire damage to any speaker system, short of being in an actual house fire.

There was melted black and red stems seen in the early A-P 25 Watt pots, later versions used an aluminum shaft.

Perhaps a scientific member can test defective plastic pot shafts in a testing oven to find out their melting point.

The person that did that damage, almost maybe, could have burned down their home, under certain circumstances.

Such as blankets hanging over them, curtains touching and doilies on top, just to name a few.

I read a while ago, likely at Crown.com, manufacturer of the Crown/Amcron amplifiers, about holding your hand in front of the woofer's dust dome, as it pumps air out.

There was mention of high heat levels from the voice coil heating up.

If I remember correctly, the temperature could go up to 150C, I believe.

There have been comments over the years of stereos causing house fires, I don't know that first hand.

The speaker wires from the amplifier to the speakers should be checked out as well.

At this point, I would suggest fuse holders be at the amplifier outlet, rather than at the rear of the speakers.

This because of the light guage wires that some users may still be using, such as the FREE speaker wires, thrown in with the stereo systems years ago.

I don't think that it was heavy enough to be used as telephone cable IMHO.

Scary!

[Tom H.]

Thanks for the input everyone.

My son and I tested the basic function of the dual capacitor (Just for the purpose of testing drivers - it will not get permanently used) by hooking up a cheap full range speaker to it to see if it somewhat cuts off the low frequencies. It more or less passed that test.

We then hotwired the mid ranges and one good tweeter through the dual cap and all drivers sounded ok to our ears. Don’t worry we kept the loudness very reduced! We also did a low level test of each woofer and they both seem fine except for the surrounds.

As it stands, all the drivers are OK except for the one bad tweeter.

I like the idea of going with the textile dome tweeter that Kent mentioned. They seem pretty reasonable cost-wise. Thanks also for listing out the parts list I’ll need. At this point I need to save some coin.

Where are you guys on the L-Pad vs. Pot “controversy”? I’ve read that some folks don’t like the sound of the l-pad vs. the original style pots. I suspect it may be one of those things that some folks swear by but I doubt that it will make much of a difference since originality is going to be pretty much thrown out the window with these speakers.

I really can’t believe these speakers didn’t burn someone’s house down. (This happened long ago before I acquired them.) One the one speaker, you can see where the back is faintly discolored from smoke/heat rising up. They must have been in the horizontal position when it happened. They also kind of smell bad inside but I should be able to rectify that. Come to think of it I kind of smell bad too but my wife keeps me around!

Thanks, Tom

[JKent]

Where are you guys on the L-Pad vs. Pot "controversy"? I've read that some folks don't like the sound of the l-pad vs. the original style pots. I suspect it may be one of those things that some folks swear by but I doubt that it will make much of a difference since originality is going to be pretty much thrown out the window with these speakers.

"Vintage AR" sells nice kits for $35 per speaker. Here's what he says:

This control is superior to the original control which AR used. It is heavy duty, has finer turns for better setability, is ventilated for heat removal and has excellent contact life. It is an "L Pad" design which holds the resistance nearly constant while adjusting the driver balance. This holds the crossover point nearly constant independent of the control setting. We have been using these on a regular basis for over ten years, have sold a great number and have never had to replace one.

Of course we know to just buy them from PE for $5 each! Check the AR3a restoration guide for comments on the L-pads.

Then of course there are the Ohmite pots. Bulletproof but hard to find, expensive, and a pain to install because you have to make some sort of shield to protect the open backs from fiberglass.

Kent

[RoyC]

Where are you guys on the L-Pad vs. Pot “controversy”? I’ve read that some folks don’t like the sound of the l-pad vs. the original style pots. I suspect it may be one of those things that some folks swear by but I doubt that it will make much of a difference since originality is going to be pretty much thrown out the window with these speakers.

Thanks, Tom

Tom,

The 25 ohm resistors in Kent's list addresses the l-pad vs pot issue. A typical 8 ohm l-pad (like those sold by "Vintage AR" and AB Tech) will change the crossover frequencies and, consequently, the tonal balance. The midrange is the area most negatively affected. The added parallel resistor will bring the l-pad's effect on the crossover much closer to that of the original pots. It is a simple and inexpensive solution to implement.

Roy