AudioCircle

Audio/Video Gear and Systems => The Vintage Circle => Topic started by: Dchristie on 3 May 2013, 01:25 am

Title: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 3 May 2013, 01:25 am
Hi folks, I am new to the AudioCircle and need some assistance identifying the inductor coil value in a pair of A25 XL speakers. I recently purchased a pair of A25 XLs and unfortunately discovered that the very fine coil leads for the tweeter inductor had been broken from the base of the coil and may not be repairable. My next option would be to replace the coil, but upon searching the net, I have not been able to find any source that provides the actual value ( mh) of the inductor. The 8.0 uf cap and 3 resistors are all readily identifiable; only the coil is unknown at this point.

I seem to recall seeing somewhere on this Site a member ( maybe Wayner)  mentioning that they thought the coil value was 0.75 mh but I would sure like to be sure before I replaced the damaged one.

If anyone can help me, I would really appreciate it !

Thanks,
 
Dean
Title: Re: Dynaco A25 XL Crossover assistance
Post by: hdspeakerman on 3 May 2013, 11:26 am
See if you can find someone nearby with a meter that can measure the inductor value.  Google search for crossover if you have not tried that.
Howard
Title: Re: Dynaco A25 XL Crossover assistance
Post by: martyo on 3 May 2013, 01:30 pm
Quote
I seem to recall seeing somewhere on this Site a member ( maybe Wayner)  mentioning that they thought the coil value was 0.75 mh but I would sure like to be sure before I replaced the damaged one.


You are correct. Wayner did refurbish a pair. They are in his normal rotation of speakers in his lab. He should notice this thread, or you could "pm" him. 8)
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 3 May 2013, 02:52 pm
Thanks for your responses. Hopefully Wayner or maybe someone else can help me. I have intensively searched the internet ( Google) to no avail and even tried to contact SEAS since the drivers were theirs and I hoped they might be able to provide some direction. Don't really have any possibility of finding someone local with a bridge to check the inductance here in Spokane, WA either.

The H086 tweeter used in the A25 XL has a resonance point of 1000hz so I really wonder how they ( Dynaco) realized the published acoustical crossover point of 1200hz for this speaker. There must be a lot of overlap with the 25 F-EW mid/bass due to it's natural roll-off as it provides a lot of signal up to 2000hz according to what I have read. I wonder what the electrical crossover point ( not final acoustical crossover) for the H086 actually is in the XL - I assume it is much higher than 1200hz as it would not have to add much below 2000hz due to the 25 F-EW carrying the majority of the signal from 2000 hz and below. Seems to me it would also be prone to power failure and also distortion if it were used much below 1800 hz or so. SEAS only recommended it as useful from 1500 - 3000 hz with a recommended power handling capacityof 5 watts. Probably why Dynaco switched to a 2nd order crossover in the XL model for this 1 inch tweeter compared to the 1st order used for the 1.5 inch dome tweeter in the classic A-25.

Makes me also wonder if another more modern tweeter could not be substituted for the H086 with a simple 1st order crossover as is done with the classic A-25. I also wonder how much different ( or alike) the 10 inch bass drivers are in each of the speakers ( original vs XL). If they are more alike than similar, maybe the current production Morel or SEAS tweeters mentioned elsewhere as suitable substitute  for the A-25would work in the XL as long as the levels were matched to the bass driver.

But, I would prefer keeping the speakers as originally designed at the present so hopefully I can repair or replace the inductor.
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 3 May 2013, 11:37 pm
Dchristie, The A-25XL is crossed over at 1500 hz. The Dynaco A-35 and A-50 were crossed at 1200 hz. I am working on a pair of Dyna-A-25Mark2's. They are the A-25XL later, 1978 with the SEAS-86 tweeter mounted right above the woofer, not to the right like the A-25XL. Wayner told me,he guessed,that the coil was .75  like you said. My speakers use a 8 ohm L-pad instead of 3 resistors like yours. Also my coil looks different from the one I saw in the A-25XL. Some where on the computer is the schematic for your cross over. I will do my best to find it. I'm going to try to send you a picture of my crossover.
(http://www.audiocircle.com/image.php?id=79794)
I know I can find it...Mark Korda
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 4 May 2013, 12:04 am
Dchristie, I was wrong,it is 1200 hz for the crossover. Mine with the L-pad are 1500 hz....sorry....Mark. I tried every thing I could on the computer and could not find it. If you ever do measure the mh of the coil, I would really like to know too....thanks,  Mark Korda.
Title: Re: Dynaco A25 XL Crossover assistance
Post by: dB Cooper on 4 May 2013, 12:21 am
Wow, a two component crossover. Who would do that today. The Dyna low-parts-count approach extended to their speakers too, obviously.  The original A25 simply had a capacitor to roll the low end of the tweeter and used the inductance of the woofer voice coil to roll its high end. They got all all fancy with the XL  :lol:
Title: Re: Dynaco A25 XL Crossover assistance
Post by: bregez on 4 May 2013, 01:55 am
Just as a visual, I am assuming your speakers have the original Dynaco A25 XL coil as shown in the image.


(http://www.audiocircle.com/image.php?id=79806)
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 4 May 2013, 05:48 am
Dchristie, this might be harder than cracking the German (Enigma Machine),I'm with you all the way brother! The value (mh) of the coil in my crossover is cemented on the board with silicone offering no data to be noted. I just got out a book that said with conventional shop equipment there is no way to measure inductance. There is a short or not. The book says all service data gives the DC resistance of coils, but Dchristie since we don't have that,I saw the bare coil of the A-25XL, and my coil has no info ,wouldn't we have to weigh the wire on a pot,whoops,a postal scale noted the mil. of the wire? ....Mark Korda
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 4 May 2013, 06:01 am
Hey Dchristie, I just re read your question about the Dyna tweeter. The ultimate tweeter that could match the Seas woofer was the Dynaudio A-28. This tweeter could go down to 1000 hz. I made a pair of speakers with them. Dynaudio does not sell their raw drivers anymore to guys like me. There was a great article in Speaker Builder magizine about the mod. I would be glad to share my copy with you...Mark Korda
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 4 May 2013, 12:59 pm
This topic again. Well, if I could find a LC meter that went down to say .5 mh, I'd buy one (if anyone knows of one) so this riddle is an interesting one.

I used to think that the coil was .75mh, but have decided that there isn't enough facts to make the call. Of course, the internet has nothing but the truth with in it. I am interested where the 1200hz cross-over point came from, cause I haven't seen it for fact, only opinion.

Anyway, we do have two clues and they are known facts. One being the cap in series at 8mfd, and there is a coil in parallel with the tweeter, so we can also safely assume that it is a 12db per octave slope.

If the cross-over were truly around 1200 (actual 1250), then the coil would be 2mh, and this would be a Linkwitz-Riley slope. I also noticed that someone said that the tweeter has a resonance frequency of 1000hz. So at 1250, one octave down would be 625hz and the signal would be down 12 db. This means that at about 1000hz, it would be down only about 6db @ the resonance frequency. Yikes.

Now, one other possibility is the good old Butterworth slope. With an 8mfd cap and a 1mh coil, that would put the cross-over at about 1750. One octave down would be 875 (close to the stated resonance frequency of 1K) with a 12db output reduction.

Or, the third possibility is that someone was "creative" and used an unknown value for the coil and we are all guessing.

So there is no final solution, other then best guess, or have someone actually measure a coil or two and finally end the guessing game.

Hint: There are speakers with much lower cross-over points, such as the Altec Lansing Santiago or Valencia that could have either a 500 or 800 hz cross-over point. That is fricken' low, man.

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 4 May 2013, 01:56 pm
Thanks everyone for your responses.

Wayner, the 1200 hz crossover came from High Fidelity Test Reports 1976 where they compared some of the design differences between the XL model A-25 and the Standard model. The original A-25 had a crossover of 1500 hz according to the test report. ( I have the test report).

The resonance frequency came from an old  detailed fact sheet from SEAS ( which I also have) which provides a lot of info on the tweeter, but interestingly, does not provide the nominal impedance info for the H086 which would have an impact on the crossover slope if indeed we are talking about a 2nd order slope. This same sheet also lists the usable frequency range for the tweeter as 1500 - 30,000 hz and the usuable range for the 25 F-EW as 35-1500 hz .

I also have the same questions about a crossover point actually being at 1200 hz as you do - if it were true, makes me wonder how all the A-25 XLs did not end up back in the shop for repairs if this figure is real (1000 hz resonance).

Now if the tweeter were truly an 8 ohm driver, textbook cap and coil values would be 7.0 uF and 0.90 mH respectively for a 2000 hz high pass crossover which seems more reasonable for a design like this and are close to the 8.0 uF cap and your estimated 0.75mH values.

If the bass driver actually has fairly substantial output up to 2000 hz or so, a 2nd order crossover on the tweeter around the same frequency might make sense.

So, the question remains unanswered at this point. Too bad  there are no info sources for schematics for some of the Dynaco equipment like there are for Acoustic Research but I am sure there is a schematic for the XL crossover somewhere in some file.

Dean
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 4 May 2013, 03:40 pm
OK Dean, good info. If in fact the cross-over is at 1200hz, then I would go for the 2mh coil. My H086 tweeters all say 8 ohms, with a resistance value of about 6 ohms. I would guess that the cross-over designer simply used the 8 ohm value to calculate the needed components. I do have a mint pair of H086 drivers that I got off of screw-bay, but they are 4 ohms, and that is why they sit in a box.

Now to the A25. I thought it had a simple 5mfd cap in series with the 8 ohm tweeter. At that point, it calculates out to 4K as the cross-over point, or do I have the cap value wrong, or is there a coil in the circuit (don't own an A25)?

So to sum up the A25XL cross-over design (at least at this point):

1) The woofer has no components and rolls off naturally (we think about 2Khz)
2) The tweeter crosses over at 1200hz, using an 8mfd, 50volt cap in series, and a 2 mh coil in parallel with the tweeter (making a Linkwitz-Riley 12db per octave slope).
3) has a 3 position, progressive resistive level switching technique. (I believe the values of the resistors are 2.2, 3.9 and 15 ohm). I think they are 10 watt, but correct if I am wrong.

I also wonder if the tweeter's polarity is reversed or not (usually done with a 12db slope).

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 4 May 2013, 05:36 pm
Wayner, you are correct in that the original A-25 ( not XL) only has a simple cap ( 5.0 uF) in series with the tweeter and 5 resistors. No inductor. looking at the tweeter crossover in my XL speaker, it appears to be in phase ( not reversed) with the woofer. I just put a battery to both drivers and they both tested in phase ( cone/dome move out with + terminals connected to + end of battery), so since each is attached the same way to the + and - terminals on the crossover board, they must also be in phase as well.

Speaker builder did a modification on the A-25 years ago and from the article, the actual crossover of the A-25 is only at the specified 1500 hz point ( as published in all of the Dynaco literature) when the series/shunt resistor combination was 11/10 ohms respectively. As you adjust the level control from this point the actual crossover for the tweeter shifts to a final value of 2500 hz where the series/shunt values end up as 2.2/18.8 ohms respectively. So the actual crossover for the A-25 speaker is variable based on the resistor combinations which makes sense.

So, if we look at the XL crossover, you have the same type of impedence shift as you add in resistance  via the level control and so I assume the crossover also varies according to the resistance added into the circuit. What I can see from looking at the crossover in my speaker is that the coil is always shunted across the tweeter + and -  terminals. Then, as you adjust the level switch from maximum output to minimum the series /shunt resistance ( in ohms) after the 8.0 uF cap adjusts ( via the different resistor combinations) as follows: 0/21 ohms, 2.2/18.9 ohms, and finally 6.1/15 ohms.  I would think that this would also affect the actual crossover point for the speaker as well.

So, maybe with the variable resistance in combination with the tweeter impedance and coil resistance, we end up with a crossover point at 1200 hz for at least one of the switch positions. We still do not know what the final resistance value would be taking everything above into account so I am not sure we can derive the final value of the coil for a 2nd order crossover without an actual measurement since the tweeter impedence is based on the whole package of the components.  Be much simpler without all of the resistors and the coil itself in the circuit

So, now my disclaimer for everything I have written above, I am not a speaker builder nor an electrical engineer so I am limited to my limited knowledge of these things but sure do wish we had a schematic. Hopefully someone more knowledgeable about such things can enlighten me.  :wink:
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 4 May 2013, 08:05 pm
I just did some math with regards to total resistance of the circuit with the 3 step resistor control. Total resistances are 5.8, 6.5 and 7.3 ohms.

When we leave the cap value at 8 mfd with the 3 different resistance values for a Linkwitz Riley, the 2 other unknowns can be solved.

So:

5.8 ohms = 8 mfd cap-----1mh coil-----cross at 1700hz
6.5 ohms = 8 mfd cap-----1.37 mh coil------cross at 1500
7.3 ohms = 8 mfd cap-----1.72 mh coil------cross at 1350

If we think it's a Butterworth

5.8 ohms = 8 mfd cap-----.5 mh coil------crosses at 1825
6.5 ohms = 8 mfd cap-----.64 mh coil------crosses at 1625
7.3 ohms = 8 mfd cap-----.86 mh coil------crosses at 1450

Here are some problems with some of the earlier statements. A 1200hz cross-over point is not possible with an 8 mfd cap. It would have to be over 10mfd. Since the 3 settings produce 3 different cross-over points (with the same coil value), the review of the speaker could not have published just one cross-over point, unless they chose the middle one (as an average).

If I were a betting man, I would pick the 2nd Linkwitz-Riley values.

Reverse engineering is a bit_h.

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 4 May 2013, 09:00 pm
I believe you are correct in that Dynaco only adressed one crossover value for their literature as they did the same for the A-25, A-35,  and A-50. All show just a single crossover point of 1500 hz, 1200 hz, and 1000 hz for each model  respectively in the literature that I have.  High Fidelty Test  Reports proably just used the manufacturers literatue for their information.

But you do have to wonder how they ( Dynaco) came up with the value of 1200 hz with the 8 uF cap in the circuit. The other thing to take into account is the values you derived in your calculations all assume a true 8 ohm driver load. Wonder what the actual impedance of the H086 is at the respective crossover frequencies as the hz increase or decrease according to the switches.

Also, that small of a coil is going to have a somewhat high DCR due to the resistance of the fine wire although coils are usually not relevant as long as their DCR is 1/20th of the driver voice coil DCR ( according to Dickason).

Dynaco appeared to be pretty thorough with their engineering ( think I read somewhere that David Hafler was involved with the development   A-25) so I have to believe their published specs for the XL have some merit to them.

Where is that ex Dynaco engineer when you need him ! :lol:

Thanks.

Dean
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 4 May 2013, 09:15 pm
Wayner,

Also, would you please share with me your solution to dislodged/broken terminals on the 25 F - EW 10 inch bass driver. Mine are not totally off the frame yet but they are very loose and won't be attached for long.

Thanks !

Dean
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 4 May 2013, 09:33 pm
PM me.

Also, I think you have to use the tweeter's "nominal" impedance (8 ohms) when figuring out the cross-over as the impedance curve of the tweeter changes with the frequency.

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: DavidS on 4 May 2013, 11:40 pm
apologies for a little off topic.  I always see these speakers for sale in good condition for $200 or less.  How do they sound - are they worth picking up.  Seems even if they don't work out with original drivers and crossover you could update with new A26 woofer and seas tweeter but not sure if this is going to be something I am happy with or just a fun experiment (and something that will sit unused in closet).
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 5 May 2013, 12:58 am
Hi David -once I have the crossovers completed, and the speakers back together, I will be glad to shoot you an opinion. I am recapping and also changing out the resistors in the crossover all with Mundorf components. Will also probably upgrade the wire to Supra 13 gauge and deoxit the level controls.

Actually, you should be able to get a better opinion from Wayner as he has rebuilt his A-25 XLs and also replaced the original cabinets with much higher quality cabinets. He has lived with his A-25XLs a lot longer than I have.

As to  how they sound, there is a huge following for Dynaco speakers - especially the original Dynaco speakers which I feel also includes the A-25 XL and A-40 XL models. If you read enough sites ( like AudioCircle) you will find some folks that absolutely love the sound of the A-25 XL and also some that prefer the original non-XL A-25 speakers which some have christened the "classic" A-25. I actually like them both and I do not feel you can go wrong with either model but it all depends on what your priorities are. To my ears they both have a very easy sound with fairly natural mids ( no bass below 45 hz or so) and smooth highs. I prefer the XL models as they have a little more high frequency extension but as I said , either is a very easy listen.

They are in pretty good demand right now so if you pick up a pair for a descent price, you can most likely resell them if you do not like them. Just be sure to listen to any used speakers carefully as a lot of them have been abused in their past lives.

Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 5 May 2013, 05:09 am
Hi Dchristie, I have the answer for you,but first,I owned a pair of Dyna A-40XL's and they were the best! At the time I was living like a loser in my mothers basement. I had 2 Dyna Mark 3 amps. The A-40XL's produced a church organ note as well as a subwoofer. I don't know if it was the cement floors?. Well Dean,I was out tonight with some thing bothering me,I think I had the solution to the unknown coil. I found the answer in David Weems speaker building book. There is a chart that shows the cross over network design of values of inductance and capacitance with speakers with impedance from 4 to 32 ohms. I'm to out of it to make any sense now,but would be glad to send a copy to you. It looks like the coil is .16mh at a cross over at 1200 hz with 8 ohm speakers. Is that what Wayner said?. Dean ,the book is Designing,Building,and Testing Your Own Speaker System wih projects by David Weems. Keep in touch, lets solve the mystery....Mark Korda
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 5 May 2013, 11:58 am
Mark,

I have that book, too. The chart on page 80 is for first order cross-overs. If you go to page 84, you will find that Butterworth and Linkwitz-Riley slopes need to have the values from page 80 modified by the formulas for the particular slope type. So the chart is good, but not the right numbers for a 2nd order (12db slope).

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 5 May 2013, 09:50 pm
Hi Wayne, I was wondering how you determine that the A-25XL has a 2nd order 12db slope. I'm not very acknowledged with cross overs. Isn't the second order cross over used for 3 way designs?On page 79 of that book it says when  a high pass filter and a low pass filter are wired together,the combination makes a full first order crossover. Isn't that what the Dyna-A-25XL cross is? I'm not dis agreeing with you,I'm trying to learn this stuff. I do get that the resistors change the cross overs frequencys  as you already stated.....remember, I went to summer school for various math studies,you got to go slow with me.....thanks Wayner....Mark
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 5 May 2013, 11:07 pm
Mark - if you look at textbook crossover designs, a first order crossover has a single capacitor in series  with the tweeter ( high pass) or just an inductor  in series with  the woofer ( low pass), respectively,  to create a 6db slope. To create a 2nd order ( 12 db slope) high pass, you would then also add a coil ( inductor) as a shunt to the tweeter and then  also a capacitor as a shunt to the woofer for the low pass. The 1st order only has one component for each driver ( either a capacitor for the tweeter or a inductor for the woofer). The 2nd order crossover has 2 components for each driver -  a capacitor and inductor - you just flip flop the positions of the components to create the high pass slope on the tweeter or the low pass slope on the woofer.

If you look at the crossover components of the A-25 XL, you have a 8.o uF capacitor in series with the tweeter and also a coil ( inductor) as a shunt to the tweeter (2 total components ). This would constitute a 2nd order crossover. The resistors are in the circuit just to adjust the level of the tweeter.
Title: Re: Dynaco A25 XL Crossover assistance
Post by: dB Cooper on 6 May 2013, 11:07 pm
deleted due to lack of math savvy
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 7 May 2013, 03:40 am
Hi Dchristie, thanks for that explanation. You made it simple to understand and very well written.If you couldn't get your hands on the meter Wayne suggested, I think if you bought a couple coils that you thought were close from Parts Express and found one that matched the size and weight of your damaged coil, their pretty good about returns, you would be up and running. Thanks for filling me in on this and you too Wayner.....Mark Korda
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 7 May 2013, 11:50 am
The coil wire of the Dynaco is really a small gauge. I don't think anyone makes coils now days with such small diameter wire. One way the coil could be measured is by undoing the wire and measuring the length, then measure the wire diameter (to determine the gauge). This would then tell what the induction would be, as I have several books here that have charts for this. But then the coil would be destroyed. No good.

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: neobop on 9 May 2013, 11:44 am
You might find this calculator useful in ballparking crossover component values.
http://www.diyaudioandvideo.com/Calculator/XOver/

There are 3 different 12dB filters listed, with different component values.  They have different Q values.

It might be easier to buy an inexpensive multimeter with inductance/capacitance measuring capability.  Parts Express used to have one for around $15, I think they still sell it.  You can order a coil made with 20 Ga wire.  I think that is the smallest ready-made Ga.  It might be better to stick with, or close to orig gauge.  The coil will have higher DCR than a heavier GA and increased resistance might be part of the design.
neo
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Mark Korda on 10 May 2013, 12:26 am
Hi Dchristie, this might not mean anything but I saw a picture of the coil for the Dyna-A25XL in Audiocarma or something like that and it was fine wire like Wayner said but it was of the color purple not copper colored. It was as purple as the Minnesota Vikings football helmets. Maybe a clue, maybe not....Mark.
Title: Re: Dynaco A25 XL Crossover assistance
Post by: neobop on 12 May 2013, 01:00 pm
I just reread this thread and Wayner is right about inductor value for 8 ohm tweeter with 8uF cap.  2.04mH for 1250Hz. 
The problem is the resistors will change the impedance of the tweeter.  Also, it's unusual for a 12dB x-over to be in normal polarity.  At the x-over frequency there will be a cancellation, a null in the response.  This is true for both 12dB Butterworth, Linkwitz and Bessel.   With a x-over point like this, I wouldn't guess that a cancellation would be part of the design. 

Years ago, 12dB Butterworth was the network of choice for manufacturers.  In phase, the drivers sum to 180 degrees out of phase.  Reverse polarity sums to + 3dB.  This would be what I would guess, the orig configuration.  Maybe the speakers were repaired previously and hooked up wrong?  Anyway, differences should be obvious once they're repaired and tried both ways.  Speaking of which, Dchristie, you said that the coil leads were broken off and unrepairable.  If you still have the broken leads it would be much easier to repair the coil.  The coil wire is coated with lacquer which first has to be sanded off.  Then you solder it back together.  A small difference in length will virtually make no difference.  Just rewind the coil back to original length.  If this can be accomplished, it is by far the easiest solution.   

Butterworth makes sense because inductor values are smaller for a given x-over frequency.  2.04mH is for an 8 ohm driver - Linkwitz, but 8 ohms might be incorrect.  If you calculate 12dB Butterworth, 1250Hz, 11.25 ohms = 8uF, 2.03mH.  The same.
http://www.parts-express.com/pe/showdetl.cfm?partnumber=255-054
neo
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Dchristie on 13 May 2013, 03:08 pm
Thanks Neo.

My speakers do not appear to have been repaired but it would be interesting to see If Wayner's A25 XL speakers are wired in phase (like mine) or reverse phase for the 2 drivers as you suggest in your post.

Wayner, you could just pull your tweeters and see if the white cable is connected to the + terminal of the tweeter. If so, I assume they are wired like mine ( in phase) unless the white lead in your speakers is also connected to the negative terminal of the crossover which would indicate that mine are wired wrong from the crossover ( highly unlikely).
Title: Re: Dynaco A25 XL Crossover assistance
Post by: Wayner on 13 May 2013, 03:31 pm
They are the same.

Wayner
Title: Re: Dynaco A25 XL Crossover assistance
Post by: bregez on 13 May 2013, 03:47 pm
I have a "new" pair of these also and the white wire goes to the red on the tweeter.
Title: Re: Dynaco A25 XL Crossover assistance
Post by: BNR_1 on 3 Oct 2013, 02:37 am
Hello Everyone:

I must have read this post so many times to get a better understanding of what folks are describing to determine the value of the air core inductor that is installed in the A25XL crossover.  In one of the postings, Dchrisite references an old spec sheets for the speakers.  I was browsing the net and by luck I came across these old spec sheets.  I attach the reference here to see if anyone can use the information to get us any closer to the value of the inductor.  In these sheets they make reference to crossover frequencies, fs, 6dB/octave so I was hoping with this information we (actually you because I have no clue) are more equipped to figure the value out.

Main site
http://www.seas.no/

On the far left click "SEAS VINTAGE DRIVERS"
http://www.seas.no/index.php?option=com_content&view=article&id=29&Itemid=63

Select "VERY OLD"
http://www.seas.no/index.php?option=com_content&view=article&id=33&Itemid=57

Then the scanned documents
Woofer - "H085 25F-EW"
http://www.seas.no/images/stories/vintage/pdfdataheet/h085_25f-ew.pdf

Tweeter - "From the 70's #2"
http://www.seas.no/images/stories/vintage/pdfdataheet/from_the_70s_2.pdf

Thank you