AR 58S Rebuild

[briodo]

I seem to have a knack for finding seriously stressed or abused AR's on Craigslist, this pair of AR 58S were found roughly 5 years ago and have been sitting on the shelf in the garage until now.  I spent time taking the woofers out and creating a list of tasks to restore them as best I can.  First some pictures.

[briodo]

I'm thinking the original 12" drivers are likely irreparable due to extensive amount of epoxy used to bind the rubber surrounds on, but hope to hear someone who may have experience with an approach.  I did have a spare pair of 12 purchased 6 years ago for another project so have replacements available.

The missing chunk of wood is on the top back of one of the cabinets and will be a challenge, but have been in a similar situation with a pair of AR90's a few years ago, so know they can be repaired to be functional, although making them look new could be a stretch.

Finally I saw lARrybody's excellent write up on crossover replacement for this model using a AR91 board, which I have for this project.  Starting my Parts Express order now!

 

[briodo]

Open to ideas on the original cabinet repair, 12" woofer recovery, and anything else I should be looking at.  I do have replacement caps for the 91 crossover boards, and will order new switches and binding posts.

[Stimpy]

Make sure that you have the correct AR91 crossover boards.  Those same "blanks" were used for both the AR91's and AR92's, which have different crossovers.  The correct 91 board, has 5 capacitors, with the woofer cap being 100uF.  The 92 board has 4 capacitors, with the woofer cap being an 80uF value.  Some different inductors too.

As to the rest, that looks like a fair amount of work.  Lots to fix.  The woofers look usable to me, but will need to be well cleaned.  Some huge surrounds on them too, which don't look correct.  So, I'm glad they're being properly restored.  Those are great speakers, and worth saving.

Good luck.

[briodo]

2 hours ago, Stimpy said:

Make sure that you have the correct AR91 crossover boards.  Those same "blanks" were used for both the AR91's and AR92's, which have different crossovers.  The correct 91 board, has 5 capacitors, with the woofer cap being 100uF.  The 92 board has 4 capacitors, with the woofer cap being an 80uF value.  Some different inductors too.

Briodo: Thanks for that.  Will post pictures of what I have for posterity and then do an inventory using correct schematic.

 

[RoyC]

4 hours ago, briodo said:

Open to ideas on the original cabinet repair, 12" woofer recovery, and anything else I should be looking at.  I do have replacement caps for the 91 crossover boards, and will order new switches and binding posts.

Those woofer cones are shot. Even if you get them to work they will not have the proper response. There is a rebuild kit available, and though it is not a precise match to the original woofer the result would be much better than the mess they are now.

Roy

[lARrybody]

4 hours ago, Stimpy said:

Make sure that you have the correct AR91 crossover boards.  Those same "blanks" were used for both the AR91's and AR92's, which have different crossovers.  The correct 91 board, has 5 capacitors, with the woofer cap being 100uF.  The 92 board has 4 capacitors, with the woofer cap being an 80uF value.  Some different inductors too.

As to the rest, that looks like a fair amount of work.  Lots to fix.  The woofers look usable to me, but will need to be well cleaned.  Some huge surrounds on them too, which don't look correct.  So, I'm glad they're being properly restored.  Those are great speakers, and worth saving.

Good luck.

Stimpy is right about the AR 91 and  AR 92 boards sharing the same blank. The AR 91 crossover has 6 resisters compared to 5 resistors on the AR 92 crossover. Yes the AR 92 uses a 80uf cap on the woofer as opposed to the 100uf cap used on the AR 91.  The AR 91 40uf cap is missing altogether. The 4uf, 8uf and 24 uf cap appear to be the same. I would not be surprised if the inductor coils have different values also. Just count the resisters (5 instead of 6) and Capacitors (4 instead of 5) to identify AR 92 boards. Identifying the inductor values will take more investigation.  As others have said, my AR58s speakers never cease to amaze me.

[ar_pro]

The AR-91 switches are really well built & very dependable - are you sure that you need new ones, Briodo?

[Stimpy]

3 hours ago, lARrybody said:

Stimpy is right about the AR 91 and  AR 92 boards sharing the same blank. The AR 91 crossover has 6 resisters compared to 5 resistors on the AR 92 crossover. Yes the AR 92 uses a 80uf cap on the woofer as opposed to the 100uf cap used on the AR 91.  The AR 91 40uf cap is missing altogether. The 4uf, 8uf and 24 uf cap appear to be the same. I would not be surprised if the inductor coils have different values also. Just count the resisters (5 instead of 6) and Capacitors (4 instead of 5) to identify AR 92 boards. Identifying the inductor values will take more investigation.  As others have said, my AR58s speakers never cease to amaze me.

Thanks!  I occasionally know what I'm talking about.  Just don't ask my wife for confirmation.  

[briodo]

1 hour ago, ar_pro said:

The AR-91 switches are really well built & very dependable - are you sure that you need new ones, Briodo?

Yep, they all measure good.  While going with new would be fun to implement, I'm thinking the originals are going to work just fine.  I will change out the old binding posts though.

[briodo]

5 hours ago, RoyC said:

Those woofer cones are shot. Even if you get them to work they will not have the proper response. There is a rebuild kit available, and though it is not a precise match to the original woofer the result would be much better than the mess they are now.

Roy

I appreciate the feedback.  One of the surrounds is marked Alpine and almost appears to come from a passive radiator they cut up and epoxied to the original cone.  There is no way I can see removing the epoxy without destroying the cone.  In addition, the wood spacer the surround attaches to was removed.  I have a spare pair, so the old ones go into the junk box.

[briodo]

4 hours ago, lARrybody said:

Stimpy is right about the AR 91 and  AR 92 boards sharing the same blank. The AR 91 crossover has 6 resisters compared to 5 resistors on the AR 92 crossover. Yes the AR 92 uses a 80uf cap on the woofer as opposed to the 100uf cap used on the AR 91.  The AR 91 40uf cap is missing altogether. The 4uf, 8uf and 24 uf cap appear to be the same. I would not be surprised if the inductor coils have different values also. Just count the resisters (5 instead of 6) and Capacitors (4 instead of 5) to identify AR 92 boards. Identifying the inductor values will take more investigation.  As others have said, my AR58s speakers never cease to amaze me.

Looks like I have the correct crossover board base on resister/cap count.  Thank you for this info! 

 

[Stimpy]

Yep those are 91 boards.  And I didn't know that AR used T.I. caps.  I believe those are Mylar.  The Unicon caps were nice too.  Both brands better than the black/red Callins capacitors in my AR90's.

Are you planning on a recap, prior to the swap?

[DavidR]

Those small value mylar caps show up on late production boards.

Attached pic>  one on an AR90 board.

 

[DavidR]

<edit for double post>

 

 

[briodo]

19 hours ago, Stimpy said:

Yep those are 91 boards.  And I didn't know that AR used T.I. caps.  I believe those are Mylar.  The Unicon caps were nice too.  Both brands better than the black/red Callins capacitors in my AR90's.

Are you planning on a recap, prior to the swap?

I purchased the replacement capacitors for 2 pairs of 91's.  I'm doing a two for one so to speak, having a pair of AR91's requiring woofer surrounds and recap.  Cabinets are 9 out of 10.  It's clear from others work in this area that NPE's from that era may need to be replaced, but mylar ones are likely to be good.  I have a meter with capacitance reading, and will verify before replacing. 

Four woofers have been refoamed.  I use shims after carefully cutting around the outside of dust cap leaving a small hinge so I can reglue.  Aileen's tacky glue works perfectly for all aspects of the job. AND drys clear.  The cut lines are barely noticeable.

Also took a picture of the crossover board still inside one of the AR91's.  It has the NPE's throughout.  AR91 also has a brace from front to back placed between the woofer and midrange drivers, assuming to reduce cabinet flex from the woofer??  I'm thinking that may be an easy add to the AR58S.  Any opinions on value of that brace?

Going to work on the crossover board removal next.

[briodo]

Should show a pic of the AR91's as well.  Still have the foam around the midrange and tweeter. 

[Stimpy]

2 hours ago, briodo said:

I purchased the replacement capacitors for 2 pairs of 91's.  I'm doing a two for one so to speak, having a pair of AR91's requiring woofer surrounds and recap.  Cabinets are 9 out of 10.  It's clear from others work in this area that NPE's from that era may need to be replaced, but mylar ones are likely to be good.  I have a meter with capacitance reading, and will verify before replacing. 

Four woofers have been refoamed.  I use shims after carefully cutting around the outside of dust cap leaving a small hinge so I can reglue.  Aileen's tacky glue works perfectly for all aspects of the job. AND drys clear.  The cut lines are barely noticeable.

Also took a picture of the crossover board still inside one of the AR91's.  It has the NPE's throughout.  AR91 also has a brace from front to back placed between the woofer and midrange drivers, assuming to reduce cabinet flex from the woofer??  I'm thinking that may be an easy add to the AR58S.  Any opinions on value of that brace?

Going to work on the crossover board removal next.

 

 

 

Beautiful work on the refoam.  Well done. 

Also, I just looked again at those 58 woofers.  I didn't realize they were that horrible.  It looks like someone glued a partial woofer on top of the AR woofer?  What were they thinking?  Brutal to see good woofers treated like that.  I'm glad you had the back-up spares!  And hopefully, you can pop out that UMR dome too?

[briodo]

Thanks Stimpy, doing surrounds is my favorite part. I bought the 58S on Craigslist from a young Mom going through a divorce for $45 in 2012 or so.  She told me her ex-husband worked in a car stereo store, which is likely source of whatever he used, which appears to be a passive radiator.  I actually tore the paper cone trying to remove the hard plastic/rubber/epoxy he used, so Tom was spot on about them being beyond normal repair.

I thought I got a heck of a deal, my wife looked at me in disbelief when I brought them home.  Glad I'm not in this for the money.

Crossovers are out and ready to work replacement caps for both pairs.  Took a picture of the AR92 and AR58S crossover boards.  BTW, I was pleased to see the 91 board connectors and switches fit the 58S back panel cutout.  I will need to figure out how to save the SN label on both AR58S

I tried a little heat and careful vacuum approach on the mid-range dome, no joy.  It is really stuck.  I've done several domes using that technique before, so something is different and appreciate some ideas on alternative methods.  I don't mind a couple of dimples, but current dent is too much...

[DavidR]

21 minutes ago, briodo said:

I tried a little heat and careful vacuum approach on the mid-range dome, no joy.

I've removed bad dents from tweeter domes by using a tube that fits over the dome and sucking on the other end (no jokes please). I also apply a small amount of isopropanol but I think the mid domes have a different coating and material. Or try to stick a thin strand of duct tape and yank it off quickly. And a third option is a very small drop/dot of Goop, wait for it to cure and tug on it gently.

[briodo]

Today was spent measuring the caps on all 6 crossover boards, qty 2 AR58S, and qty 4 AR91.  I included the replacement Dayton NPE replacement caps in the measurement test as well.  No surprises.  Collins were way out, Unicom had good and bad, the TI's were 3 for 4 within tolerance.  My baseline assumption of 5% tolerance is acceptable.

I will be replacing all the caps on the AR91 crossovers due to age.  However, my lesson on using Daytons (especially when doing series or parallel to reach target value) is to measure them before use.  The 22uf I purchased all measured within tolerance without combining with the 2.2uf to reach the target 24uf goal for what I called C3.

results attached for those who appreciate measurements. 

AR58S and AR91 Cap Value Measurements.pdf

[briodo]

12 hours ago, briodo said:

The 22uf I purchased all measured within tolerance without combining with the 2.2uf to reach the target 24uf goal for what I called C3.

 

Rethinking this comment, will remeasure tonight using 22 + 2.2 combo.  Otherwise I'm deviating from specified parts and that is a slipper slope.

[AR surround]

12 hours ago, briodo said:

Today was spent measuring the caps on all 6 crossover boards, qty 2 AR58S, and qty 4 AR91.  I included the replacement Dayton NPE replacement caps in the measurement test as well.  No surprises.  Collins were way out, Unicom had good and bad, the TI's were 3 for 4 within tolerance.  My baseline assumption of 5% tolerance is acceptable.

I will be replacing all the caps on the AR91 crossovers due to age.  However, my lesson on using Daytons (especially when doing series or parallel to reach target value) is to measure them before use.  The 22uf I purchased all measured within tolerance without combining with the 2.2uf to reach the target 24uf goal for what I called C3.

results attached for those who appreciate measurements. 

AR58S and AR91 Cap Value Measurements.pdf 30.98 kB · 7 downloads

I replaced the Unicon caps in Boston A70's with Dayton NPE's. (Note that there is only one cap in this 2-way Boston.)   The result was not good compared to the Unicons...harsh mid/upper range.   I had to add 1/2 ohm of resistance and a subsequently a Dayton F&F bypass cap to restore the tonal qualities of the speaker to my liking.   I conjecture that the ESR of the stock Unicon capacitors is higher than that of the Daytons.  Just communicating my experience in case you don't like the results with the Daytons.

[briodo]

5 hours ago, AR surround said:

I replaced the Unicon caps in Boston A70's with Dayton NPE's. (Note that there is only one cap in this 2-way Boston.)   The result was not good compared to the Unicons...harsh mid/upper range.   I had to add 1/2 ohm of resistance and a subsequently a Dayton F&F bypass cap to restore the tonal qualities of the speaker to my liking.   I conjecture that the ESR of the stock Unicon capacitors is higher than that of the Daytons.  Just communicating my experience in case you don't like the results with the Daytons.

That is really good to know.  I found a post from 2011 started by Carlspeak on capacitor values and will spend more time researching.  I don't need to rush this repair and the sunk cost of the Dayton's are not going to force my decision if a better option is out there.  It is clear the old ones have to go, just want to be good enough to represent the original design/sound knowing the surrounds will need to be redone in 20 years... 

[DavidR]

29 minutes ago, briodo said:

Dayton's are not going to force my decision if a better option is out there.

I've used the Dayton (made by MDL) and they are fine. Mundorf has some ECap70 NPE that I use on the smaller values. The larger value Mundorfs don't have a sufficient voltage rating compared to what AR used. CSP member Harry398 has done several AR restorations and used the Dayton NPE and he was always happy. You might drop him a PM for his thoughts.