Dynaco A-25 Restoration - Measurements - Comments

[Pete B]

Thanks for the interesting input Vern, I've never seen the insides of an A-50.

Yeah, about marketing literature, I had to go work in the real world to learn about "dog and pony" shows:

From: http://en.wikipedia.org/wiki/Dog-and-pony_show

"The term has come to mean any type of presentation or display that is (1) somewhat pathetically contrived or overly intricate or (2) put on for purposes of gaining approval for a program, policy, etc."

I was wondering, have you ever seen and F-EW type woofer with this type of cone used in any production Dynas:

http://www.classicspeakerpages.net/dc/dcbo...d=141&page=#150

Best,

Pete B.

[Pete B]

I've mentioned that the 25F-EW (H250) does not seem right. The one I have came in an A-25 system,

and I thought it was the only version.

I just noticed on the Madisound site that the 25F-EW that they suggest is the different H085 version.

http://www.madisound.com/cgi-bin/index.cgi...=3D%25&pid=1035

Here's a picture, note the mostly uncoated paper cone and the different dust cap as compared to the early 25F-EW:

http://www.madisound.com/images/product/H085.jpg

And here is the H250 version, from 1990 (date code 48/90) that I've been talking about, note the fully coated cone:

http://members.aol.com/basconsultants/25F-EWF.jpg

http://members.aol.com/basconsultants/FEW2.jpg

Here is an older 25F-EW, from 1976 (date code 42/76) that appears to

have exactly the same cone as the original 25TV-EW:

http://www.classicspeakerpages.net/dc/user_files/1495.jpg

http://www.classicspeakerpages.net/dc/user_files/1494.jpg

I believe that the H085 is probably the closest SEAS 10" to what was used in the A-25XL

and is probably a good, but more efficient replacement for the old 25TV-EW.

My comments about the F-EW only apply to the H250 version that I heard/measured.

[Guest DaveyU]

Pete,

I read your posts. Wow, you really are "the man" when it comes to integrity of sound. I have two A25s that need woofers. I found Madisound and was a litte distressed by your review of their replacements. (My current woofers are not coated paper but look more like the ones on Madisound's website.) I also found woofers advertised as original used with the model number of #25 TV-EW. Are these, in fact, the correct item number?

What are your thoughts?

Thanks.

[Guest DaveyU]

Pete,

I read your posts. Wow, you really are "the man" when it comes to integrity of sound. I have two A25s that need woofers. I found Madisound and was a litte distressed by your review of their replacements. (My current woofers are not coated paper but look more like the ones on Madisound's website.) I also found woofers advertised as original used with the model number of #25 TV-EW. Are these, in fact, the correct item number?

What are your thoughts?

Thanks.

[Pete B]

Hi Dave,

Thanks for your generous comments.

Maybe it didn't come across in my last post but I was mistaken, thinking there was only one 25F-EW, there are two different H versions, H085 and H250. I purchased these A-25s recently and

one had an 25F-EW H250 which is not what Madisound suggests and

is simply the wrong woofer.

I've not heard or measured the H085 but it looks very close to

the FEW that was probably used in the A-25XL.

You say you need new woofers, why are they damaged, or do you

think they're the wrong ones?

Are you sure you've got A-25s (1.5" tweeter, 5 pos switch) and not A-25XLs (1" tweeter 3 pos switch)?

If you have A-25s and you want original woofers, then yes I'd look

for 25TV-EW 8 ohm woofers on ebay.

If you have A-25XLs or want to try an XL type woofer, then you can look for an old 25F-EW on ebay, or the new one from Madisound, but

not the H250.

Please let us know about your findings.

>Pete,

>I read your posts. Wow, you really are "the man"

>when it comes to integrity of sound. I have two A25s that need

>woofers. I found Madisound and was a litte distressed by your

>review of their replacements. (My current woofers are not

>coated paper but look more like the ones on Madisound's

>website.) I also found woofers advertised as original used

>with the model number of #25 TV-EW. Are these, in fact, the

>correct item number?

>

>What are your thoughts?

>

>Thanks.

[Guest DaveyU]

Pete,

I definitely have the A25s with the larger tweeter. And the reason I need woofers is because years ago a house sitter of mine must have crank the music very loud for a long time (while I was away). When I returned the speakers sounded awful. The cones look fine but I'm just guessing that the magnets were fried. I guess I should check that out but I don't know what to look for.

Could something else be causing the bad sound?

How could I check this out myself?

Thanks for your generosity.

Dave

>Hi Dave,

>

>Thanks for your generous comments.

>Maybe it didn't come across in my last post but I was

>mistaken, thinking there was only one 25F-EW, there are two

>different H versions, H085 and H250. I purchased these A-25s

>recently and

>one had an 25F-EW H250 which is not what Madisound suggests

>and

>is simply the wrong woofer.

>I've not heard or measured the H085 but it looks very close

>to

>the FEW that was probably used in the A-25XL.

>You say you need new woofers, why are they damaged, or do you

>think they're the wrong ones?

>Are you sure you've got A-25s (1.5" tweeter, 5 pos

>switch) and not A-25XLs (1" tweeter 3 pos switch)?

>If you have A-25s and you want original woofers, then yes I'd

>look

>for 25TV-EW 8 ohm woofers on ebay.

>If you have A-25XLs or want to try an XL type woofer, then you

>can look for an old 25F-EW on ebay, or the new one from

>Madisound, but

>not the H250.

>Please let us know about your findings.

[Pete B]

Thanks again Dave,

OK, I understand. As I mentioned back in the thread the original TV

woofer voice coil was wound on a paper former, this compared to the

Advent for example with a solid metal former did not handle much

power at all. Played loud, the coil will overheat and deform, even

burn the paper former. You probably have burnt and/or partially

shorted windings or one that is badly deformed and not moving freely.

The only way to bring them back to original condition is to find

new/used woofers on e-bay for example. This is what I did because I

wanted a completely stock pair for historical reasons. We can give

you some tips for buying on e-bay if you'd like.

Also keep in

mind that not only do the paper former woofers burn out more easily,

they heat up more easily under normal playing and the copper

resistance goes up, you might be surprised by how much, which leads

to what we call thermal compression. The woofer output fades by

a few dB as they heat up.

I believe that the Madisound 25F-EW is a good replacement, but

remember that it is about 3 dB more efficient, and you might want

to add/move one wire in the crossover to raise the tweeter level

as compensation. We're fairly

certain that the 1976 F-EW was used in the more efficient A-25XL.

I'm also fairly certain that it has a better voice coil former,

will handle more power, and will have less thermal compression.

I believe that the stronger motor will result in slightly less

bass output at the lowest end of the woofer range due to the

stronger damping. I've not tried or tested the 25F-EW H085 version

so this is what I expect based on the theory, T&S parameters, and

published response curve for the 25F-W H085. Another alternative

is to pad the H085 woofer with some series resistance to weaken

the motor and make it more like the original while retaining the

better thermal capacity. I worked out the resistor values for the

F-EW that I have and they should work for the H085 if you'd like

to try it. Nice thing about this is you can try it both ways.

Pete B.

>Pete,

>

>I definitely have the A25s with the larger tweeter. And the

>reason I need woofers is because years ago a house sitter of

>mine must have crank the music very loud for a long time

>(while I was away). When I returned the speakers sounded

>awful. The cones look fine but I'm just guessing that the

>magnets were fried. I guess I should check that out but I

>don't know what to look for.

>

>Could something else be causing the bad sound?

>How could I check this out myself?

>

>Thanks for your generosity.

>

>Dave

[Horswispr]

There's a pair of F EWs on Ebay as I write. I'm thinking of snapping them up just as a back up. Wound up with a pair of A-25s recently with a blown woofer. Fortunately the guy was local and cool so didn't have to deal with finding a replacement woofer at that time. But it could happen again. I'm a wood guy, not a driver guy (though I could replace a Dynaco woofer or tweeter).

My question is this: Would the F EW with the round outside fit into a typical SEAS early 70s Dynaco cabinet? The woofers of that era had the same cone as the "roundie" F EW, but with the star screw insert pattern. Would a roundie not fit into the typical 1970-1972 woofer space?

The round pattern was what I associate with the Scaspeak woofers of teh 1969 Dynaco A-25s, with the port on the top.

Anyone know?

--Horse

[dynaco_dan]

Hi there;

The round woofer will fit into the horned hole ok.

The horned woofers require that you knotch the cabinets for the horns, with a wood chisel, a minor job.

Good luck.

[Pete B]

Has anyone found a close match in replacement grille cloth?

These did not have grilles and I just need the cloth for a

replacement pair. I've seen the various discussions of the

more coarse cloth used on Advents and ARs but I'm looking

for a close match to the origianal A-25 cloth. Anyone?

[onplane]

I found the pic below on AK and it's supposed to be the xover of an A-25. I've seen written many times that the A-25 has no coil in the woofer xover, yet there clearly is one in this pic.

Any guesses as to what's going on here?

Regards,

Jerry

http://www.classicspeakerpages.net/dc/user_files/1862.jpg

[dynaco_dan]

>I found the pic below on AK and it's supposed to be the xover

>of an A-25. I've seen written many times that the A-25 has no

>coil in the woofer xover, yet there clearly is one in this

>pic.

>

>Any guesses as to what's going on here?

>

>Regards,

>Jerry

>

Hi Jerry;

The item above the cap is also strange, looks like a funny resistor or funnier cap, possibly an owners add-on.

This is not an A-25 crossover.

[Pete B]

>I found the pic below on AK and it's supposed to be the xover

>of an A-25. I've seen written many times that the A-25 has no

>coil in the woofer xover, yet there clearly is one in this

>pic.

>

>Any guesses as to what's going on here?

>

>Regards,

>Jerry

>

>http://www.classicspeakerpages.net/dc/user_files/1862.jpg

>

It has 5 resistors on the tweeter switch which is correct for an A-50. The woofer section is too simple for an A-50:

http://www.classicspeakerpages.net/dc/dcbo...g_id=&page=#106

It could be a normal A-25 that had the woofer replaced with the newer XL version. One tweeter resistor would be removed. The woofer inductor would help with the newer, more efficient woofer. The extra cap in the tweeter circuit looks to be like the modification that I suggested:

http://members.aol.com/basconsultants/DYNACO-A25-XO.htm

[Pete B]

Anyone know if Dynaco used a black cloth behind the light grille cloth or did they just paint the grille frame black?

>Has anyone found a close match in replacement grille cloth?

>These did not have grilles and I just need the cloth for a

>replacement pair. I've seen the various discussions of the

>more coarse cloth used on Advents and ARs but I'm looking

>for a close match to the origianal A-25 cloth. Anyone?

[Pete B]

Aperiodic Vent link, see previous post.

[Pete B]

I have finally made new grilles for these speakers.

I estimated the thread count at 28, however I'm wondering now if it might have been 18. It would help if someone with original grilles would please count the threads per inch.

I spoke to Roy C. who spends more time here on the AR forum and commented about how excellent his AR-2ax's looked:

http://www.classicspeakerpages.net/dc/dcbo...pe=search#11164

That material, in his first picture, is 18 ct, and it has the most open weave that I've seen so far. The texture is more of an expensive linen and it looks very close to the original Dyna A-25 material. Roy offered his source as:

http://www.123stitch.com/cgi-bin/fabric.pl

It is under linen, 18 ct, "Lambswool" color.

I estimated the count as closer to 28 but this was based on pictures and memory. I completed these grilles using "Zweigart 100% Linen, 28 Count, Cashel Raw Linen" purchased at a Michael's store. The color is a bit darker than what I remember and I believe that the 18 CT linen mentioned above is a better match.

[Pete B]

Grille Cloth link

[Pete B]

Vern wrote from:

http://www.classicspeakerpages.net/dc/dcbo...=97&mesg_id=350

>Hi Pete;

>

>Have you continued with your A-25 investigation?

>

>How are you making out?

>

>I kept a printout of your great schematic, 2/24/06 Rev 1.0 and

>started to look from where I copied it from.

>

>Thank goodness the Dynaco forum doesn't have thousands of

>files, it wasn't too difficult to find.

>

>I wrote elsewhere, without seeing your comment, about that

>A-50 schematic not being in my mind, correct as well.

>

>I feel the 10 ohm w-w resistor in series at the lowest

>setting, is incorrect.

>

>This would place the tweeter down at least 10 db +/- for

>starters.

>

>It would be appropriate to have it at the end of the switch to

>common ground, such as with the A-25 crossover.

Hi Vern,

I bought these with the intention of mainly investigating the Aperiodic woofer loading, and they were not in great shape.

I ended up refinishing them, making new grills, they were missing when I got them, and finding a new woofer to replace the newer FEW type.

I spent a lot of time looking for a close match to the grill cloth but I didn't have the original so it was a best guess. Still would like someone to count the threads per inch on an original pair of A-25s and report it here.

I'm going to have a look at the tweeters, take some measurements and then close them up and hopefully be done with them for now.

I'm not in a rush to do some detailed bass experiments, I just saw them for sale near by and picked them up.

It will be nice to have a restored pair as a reference for the original sound.

[Pete B]

Vern wrote from:

http://www.classicspeakerpages.net/dc/dcbo...=97&mesg_id=350

>Hi Pete;

>

>Have you continued with your A-25 investigation?

>

>How are you making out?

>

>I kept a printout of your great schematic, 2/24/06 Rev 1.0 and

>started to look from where I copied it from.

>

>Thank goodness the Dynaco forum doesn't have thousands of

>files, it wasn't too difficult to find.

>

>I wrote elsewhere, without seeing your comment, about that

>A-50 schematic not being in my mind, correct as well.

>

>I feel the 10 ohm w-w resistor in series at the lowest

>setting, is incorrect.

>

>This would place the tweeter down at least 10 db +/- for

>starters.

>

>It would be appropriate to have it at the end of the switch to

>common ground, such as with the A-25 crossover.

Hi Vern,

I bought these with the intention of mainly investigating the Aperiodic woofer loading, and they were not in great shape.

I ended up refinishing them, making new grills, they were missing when I got them, and finding a new woofer to replace the newer FEW type.

I spent a lot of time looking for a close match to the grill cloth but I didn't have the original so it was a best guess. Still would like someone to count the threads per inch on an original pair of A-25s and report it here.

I'm going to have a look at the tweeters, take some measurements and then close them up and hopefully be done with them for now.

I'm not in a rush to do some detailed bass experiments, I just saw them for sale near by and picked them up.

It will be nice to have a restored pair as a reference for the original sound.

[Rolf Zetterberg]

On my A25s,the version with Scan-Speak tweeter and SEAS woofer,it's around 25 threads per inch -one thread per mm-although it could very well be made in India or whatever.It's not evenly woven though,about every inch or so there's a thicker thread and also some extra thicker threads woven in uneven intervals.Sounds a little complicated,I guess.I'll see if I can scan the fabric.

[Pete B]

>On my A25s,the version with Scan-Speak tweeter and SEAS

>woofer,it's around 25 threads per inch -one thread per

>mm-although it could very well be made in India or

>whatever.It's not evenly woven though,about every inch or so

>there's a thicker thread and also some extra thicker threads

>woven in uneven intervals.Sounds a little complicated,I

>guess.I'll see if I can scan the fabric.

Thanks very much for this, I used some thing close to that and it does look very good so it should be fine.

[Pete B]

The 1.5" SEAS H-087 (ALNICO magnet) tweeter was the one most commonly

used in the A-25. It can be seen here in this picture, thanks Vern:

http://www.classicspeakerpages.net/dc/user_files/1871.jpg

This large tweeter was probably in an attempt to provide better power

handling. However, this tweeter utilized a paper voice coil former

which does not function as much of a heat sink. Aluminium or

aluminized paper is much better.

The H-087 was a good tweeter for its day, but it was a dated design

even in the early 1970s. The SEAS 27TFFC suggested as a modern day

replacement is a far superior tweeter.

It does employ tinsel lead in wires which helps to avoid wire breaks

with first order crossovers.

It is a simple design with a felt pad under the dome, no pole vents

or chambers to add resonances to its response.

[Pete B]

I noticed that one of the two systems here sounded harsher in the midrange than the other, it was subtle and I was not positive that it was a speaker problem. I decided to open the tweeters and take a look.

I have quite a bit of experience with older dome tweeters and midranges that often did not have any sort of alignment pins for centering the voice coil. In this case you play a test tone at resonance and adjust the position until there is no voice coil rub or buzz, then tighten the screws.

The SEAS H-087 has a thin donut shaped ring in the frame, and a matching ring shaped depression in the dome assembly which is used to center the dome.

Removing the four screws in front allows the front face plate to be removed. This is not something to do if you do not have a gentle touch since it is very easy to damage or deform the voice coil in the process. I inspected everything once the dome was off and checked for debris in the gap. One driver did have a small piece of metal lodged in the gap, which I removed. Otherwise, both looked fine, voice coils looked good, and were reasonably centered. I also cleaned the two alignment surfaces to be sure that they would match up without binding.

One tweeter went back together without any buzz issues. The other was sensitive to the order in which the screws were tightened and there was a definite buzz when not reassembled correctly. I found a combination of pressure toward one side and the correct order in tightening the screws eliminated the buzz. Even modern tweeters from top name suppliers have consistency issues and I have often seen misaligned voice coils and other problems.

These tweeters otherwise look to be in very good shape.

[Pete B]

I should probably mention that it is easy to see the buzz in an impedance measurement or even better by measuring the distortion at the driver terminals when driven by a high Z source. This allows distortion on the acoustical side to be reflected back into the primary side. I did this and could easily see the distortion with the driver that buzzed. I could have gotten out my mic, but the driver was already wired up for this test and it worked fine.

[Pete B]

Finally measured the original capacitors in this pair of Dynaco A-25s.

One unit has a Jensen 5 uF made in Denmark cap, and the other has a Wicon

cap, both 5 uF 50V. It seems that the Wicon is defective showing very high

ESR of about 12 ohms:

5uF 50V Jensen:

2 kHz 5.11 uF + .75 R

3 kHz 5.07 uF + .60 R

5 kHz 5.02 uF + .45 R

5uF 50V Wicon:

2 kHz 4.48 uF + 12.3 R

3 kHz 4.47 uF + 12.1 R

5 kHz 4.50 uF + 12.0 R