Dynaco A25 Speakers

mresseguie · « **on:** 20 Feb 2020, 07:45 pm »

I've got a pair of A25 speakers that I bought from a guy on Craigslist about a year ago. I bought them because I wanted to hear what they sound like. After all, they're famous and practically everyone has heard a pair, right? Well, I hadn't. Now I've heard them.

The guy who sold them had monkeyed with the front baffle <which didn't worry me at the time>. It wasn't until after I had paid him my $200 and he was driving off that I removed the woofer in order to see just how screwed up the speakers were. It turned out that the front baffle portion that held the driver's screws in place had rotted out, so this guy had used caulk/liquid nails/black goopy gunk to 'seal' the woofers to the baffle. Of course, this throws the sound off.

Anyway, the speakers have sat in my office for a year now. I'm not going to listen to them. I've considered offering them up for sale; selling just the drivers (all 4 work) and keeping the cabinets for a future project, or just tossing them in the garbage when no one is looking. I could even offer them as a KARMA (recipient would have to pay for shipping!).

Anyone have suggestions? How should I handle this?

Michael

Wind Chaser · « **Reply #1 on:** 20 Feb 2020, 08:03 pm »

Start a museum.

As with so many classics, I haven't heard them myself. I doubt it would be worth your time to do a restore. Episodes like this have taught me to quell curiosity and impulse.

Folsom · « **Reply #2 on:** 20 Feb 2020, 08:50 pm »

Pictures please. They have gunk to seal them from the factory (it's not glue though). I'm not sure anything sounds off about them yet. I like them personally buy recognize they aren't perfect and maybe not for use in ones primary stereo.

mresseguie · « **Reply #3 on:** 20 Feb 2020, 09:00 pm »

Cell phone quality:

I think you can make out that the baffle is still intact, but the seller must have thought the screws were no longer capable <alone> of securing the woofer drivers. My original idea was to hire a guy locally to make me new front baffles. However, I'm not so enamored of their sound that I want to go to the expense or trouble of reconditioning this old pair.

HAL · « **Reply #4 on:** 20 Feb 2020, 09:06 pm »

The woofer sealant on my Dynaco A25's is one that does not dry. Had to carefully peel the woofer out of its mounting hole.

Got lucky and found an A25 and A25XL that had tweeters mounted as mirror image pair. Sound very good for their age. Replacing the tweeter series connected electrolytic cap with a Solen PP film made a big difference in sound quality as did cleaning the attenuator switch contacts.

Folsom · « **Reply #5 on:** 20 Feb 2020, 09:16 pm »

Those are bone stock, probably never opened before. Totally factory and just fine. They aren't exactly meant to be played without the grilles...

They need a new capacitor if the tweeter isn't blown, and some fresh goo, that's it.

planet10 · « **Reply #6 on:** 20 Feb 2020, 09:19 pm »

The cabinets are worth burning.

The drivers can be used to build a decent speaker (i suggest removing the tweeter grill, use plywood and mirror image the boxes.and rebuilding the XO). The A35 cabinet is probably a better place to put them. Scott and i also did a modern classic TL for the SEAS current similar woofer and should work fine.

You will also find the parts are worth more than the drivers & the box together (and a lot easier to ship).

Drawings for A10/A25/A35/40 here:

https://www.t-linespeakers.org/classics/dynaco.html

The big TL; http://p10hifi.net/tlinespeakers/FAL/box-plans/classicTL-revisited-WD.pdf

dave

mresseguie · « **Reply #7 on:** 20 Feb 2020, 09:25 pm »

Picture me slightly slack jawed in wonder that the goopy stuff on my baffles is supposed to be there!?!?! Huh....

I had considered replacing the cap, but I think I'm better off handing them over to someone in greater need than myself. I anticipate the need to sell gear in order to be able to downsize. [No, my Apollos are not for sale.]

Thanks, guys.

Michael

Mark Korda · « **Reply #8 on:** 20 Feb 2020, 09:45 pm »

Hi Hal,
That's no problem. Very carefully take a 1 inch putty knife and some rags and scrape up that gorpy glue. You want to be careful to not bring up any of the particle board. Fill the old holes with some silicone caulking and scrape them flat with your putty knife once the black gorpy stuff is cleaned up.
Get a roll of Mortite at the hardware store.It's like modeling clay on a string. It comes in a big roll and is used to fill cracks in old wooden windows and can be pulled out for the summer. It's the easiest way to make a uniform woofer gasket that does not harden and does not get goopy. When you put your woofer back in note where the old holes were and move the woofer over 1/2 an inch....remember to make new pilot holes smaller than the screws diameter. Protect that woofer from any slips of your hand! I know from experience.
I noticed that little point of crumbled particle board. One pair I fixed looked exactly like yours I put a Mortite gasket in an just kept it abutted against the woofers edge around the routed edge of the woofer cabinet hole.When your screws are in place it will be air tight I did the same with the tweeter. Don't over tighten the screws,the gasket does a job of holding too. The Mortite doesn't even squeeze out,it was made for Dyna it seems.
I saved 2 different Dynaco woofer gaskets. They were a cheap way out,foam, and are as thin as a piece of paper. I forgot wipe the black crap off the woofer frame too. When your done you will have a better Dynaco A-25 than before,,,,,Mark.

Folsom · « **Reply #9 on:** 20 Feb 2020, 09:46 pm »

Wow, please don't butcher them. Despite being the number one made speaker in the world there isn't a pile of them around for us to pick them up for nothing and enjoy.

The aperiodic vent at the bottom is special tuned, and for the tuning to work it needs to be very well sealed.

HAL · « **Reply #10 on:** 20 Feb 2020, 10:11 pm »

Quote from: Mark Korda on 20 Feb 2020, 09:45 pm

Hi Hal,
That's no problem. Very carefully take a 1 inch putty knife and some rags and scrape up that gorpy glue. You want to be careful to not bring up any of the particle board. Fill the old holes with some silicone caulking and scrape them flat with your putty knife once the black gorpy stuff is cleaned up.
Get a roll of Mortite at the hardware store.It's like modeling clay on a string. It comes in a big roll and is used to fill cracks in old wooden windows and can be pulled out for the summer. It's the easiest way to make a uniform woofer gasket that does not harden and does not get goopy. When you put your woofer back in note where the old holes were and move the woofer over 1/2 an inch....remember to make new pilot holes smaller than the screws diameter. Protect that woofer from any slips of your hand! I know from experience.
I noticed that little point of crumbled particle board. One pair I fixed looked exactly like yours I put a Mortite gasket in an just kept it abutted against the woofers edge around the routed edge of the woofer cabinet hole.When your screws are in place it will be air tight I did the same with the tweeter. Don't over tighten the screws,the gasket does a job of holding too. The Mortite doesn't even squeeze out,it was made for Dyna it seems.
I saved 2 different Dynaco woofer gaskets. They were a cheap way out,foam, and are as thin as a piece of paper. I forgot wipe the black crap off the woofer frame too. When your done you will have a better Dynaco A-25 than before,,,,,Mark.

Hi Mark,
Those are mresseguie's A25's in the pictures.

Mine are in very good shape and sealed back up after the cap replacement.

Best,
HAL

planet10 · « **Reply #11 on:** 20 Feb 2020, 10:33 pm »

Over a million Dyna A25s were shipped, built by at least 2, maybe 3 OEMs. I expect that ove rthe entire popullation there are many variations.

dave

Folsom · « **Reply #12 on:** 20 Feb 2020, 11:20 pm »

IIRC there's only one minor difference between some of the models. The only thing you need to check is the uf value of the cap that needs replaced in all of them. Then you need some fresh goo from parts express, and a little deoxit to clean the switch. And I recommend some gloves for handling the mineral wool, not because it's nasty like fiberglass, but because it feels funny and leaves little bits of minerals on your hand you wash off. The soldering is slightly tricky because it's through the woofer hole.

dB Cooper · « **Reply #13 on:** 21 Feb 2020, 05:19 am »

What I know about the A25:

I enjoyed mine very much for the ~9-10 years I used them.

The A25 had the simplest crossover imaginable (a single capacitor in series with the tweeter to keep the low frequencies out), probably one reason it was renowned for its transient response. Crossover was a relatively low 1500 Hz. The aperiodic tuning gave it very tight,articulate bass and a smooth impedance curve that made it an easy load for an amp. The bass tuning was accomplished by feeding it a low frequency square wave and adjusting the amount of stuffing in the port while observing the woofer output on an oscilloscope.

The later A25XL had a slightly more complex crosseover, a slightly smaller tweeter and about 3dB higher sensitivity.

I don't know where Wayner is but he is also a good resource for A25 know-how. He built beautiful replacement cabs for his. That's who I'd reacjh out to for advice. His A25 pictures are gone (below are a couple I saved) and maybe he is too but Frank Van Alstine might know how to reach him.

Folsom · « **Reply #14 on:** 21 Feb 2020, 06:01 am »

Nice new boxes, but the tweeter will never be pretty!

Mark Korda · « **Reply #15 on:** 22 Feb 2020, 12:33 am »

Hi you guys,
I looked again at the pictures and would like to add a little. Some earlier A-25's used a ScanSpeak woofer, not the more common Seas.The ScanSpeak has little bumps around the screw holes on the woofer frame while the Seas does not. So you might not be able to use new pilot holes.Once you de-gorp ,clean up the woofer hole and put a dab of caulking in the existing screw holes.The Mortite gasket you will have made does 90 percent of keeping the woofer in there anyway, like Blu-tack poster putty.
Folsum, I don't want to be mean but I couldn't even unfurl my roll of Parts Express speaker gasket material. It became a mess and I had to give it the heave ho.My roll of Mortite,and you get enough to do 100 speakers is still just as pliable as it was new 25 years ago.In my old apartment windows in Maine it dried out after a few years but that was Mortite exposed to mother nature not your listening room.I'm a big Parts Express fan though,there great.
Why put gorpy gunk back in when it shouldn't of been there to begin with. I will get some pictures including the sheer thin gasket Dyna used.When you make your Mortite gasket it's so easy it's like going back to kindergarten and playing with modeling clay. Scrinch in some little pieces around those screw holes...take care Mark Korda

planet10 · « **Reply #16 on:** 22 Feb 2020, 12:39 am »

Quote

Some earlier A-25's used a ScanSpeak woofer,

In the A25s built by SanSpeak?

dave

SET Man · « **Reply #17 on:** 22 Feb 2020, 02:23 am »

Quote from: dB Cooper on 21 Feb 2020, 05:19 am

What I know about the A25:

I enjoyed mine very much for the ~9-10 years I used them.

The A25 had the simplest crossover imaginable (a single capacitor in series with the tweeter to keep the low frequencies out), probably one reason it was renowned for its transient response. Crossover was a relatively low 1500 Hz. The aperiodic tuning gave it very tight,articulate bass and a smooth impedance curve that made it an easy load for an amp. The bass tuning was accomplished by feeding it a low frequency square wave and adjusting the amount of stuffing in the port while observing the woofer output on an oscilloscope.

The later A25XL had a slightly more complex crosseover, a slightly smaller tweeter and about 3dB higher sensitivity.

I don't know where Wayner is but he is also a good resource for A25 know-how. He built beautiful replacement cabs for his. That's who I'd reacjh out to for advice. His A25 pictures are gone (below are a couple I saved) and maybe he is too but Frank Van Alstine might know how to reach him.

Hey!

Man! Those are pretty. I don't mind the look of those tweeters.

I've never heard them. But I think the key of these speakers is that those woofers are running full range and naturally rolled off just a right point and steep enough for the tweeters to come in, so no need for the crossover for the woofer. I love the design of these speaker.

Anyway, here's a modern day A25, the Seas A26 kit.

https://www.madisoundspeakerstore.com/2-way-speaker-kits/seas-a26-10-2-way-kit-pair-based-on-the-classic-a25/

Buddy

planet10 · « **Reply #18 on:** 22 Feb 2020, 04:04 am »

The tweeters in the gorgeous rebuild look like the newer ones from the A25XL.

Quote

Seas A26 10" 2-way Kit

That’s the kit we designed the big TL for.

Link to plans posted earlier.

dave

dB Cooper · « **Reply #19 on:** 26 Feb 2020, 03:32 am »

Quote from: SET Man on 22 Feb 2020, 02:23 am

Hey!

Man! Those are pretty. I don't mind the look of those tweeters.

I've never heard them. But I think the key of these speakers is that those woofers are running full range and naturally rolled off just a right point and steep enough for the tweeters to come in, so no need for the crossover for the woofer. I love the design of these speaker.

Anyway, here's a modern day A25, the Seas A26 kit.

https://www.madisoundspeakerstore.com/2-way-speaker-kits/seas-a26-10-2-way-kit-pair-based-on-the-classic-a25/

Buddy

The woofer is not run full range. The inductance of the woofer (according to contemporary reviews) rolls the woofer at 1500 Hz and the cap on the tweeter acts as a high-pass. I'm guessing the slopes are gentle. The XL had a slightly more complex x-over.