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.

>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.

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.

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.

>Thanks Pete. > >I just wrote up a rather lengthy post about refoaming that >will probably bore most readers to tears but there you have >it. > >I have been following your measurments regarding the New >Advent and variations and this is the type of information that >should be made a "pinned" thread if any. > >That and maybe practical applications such as >refoaming/rebuilding as you mentioned in another thread. > >Regards, >Doug Hi Doug, I did enjoy reading your thread, good to see you get them in perfect working order. I think Mark is probably too busy to worry about pinning threads, perhaps he would make you a moderator with that ability, that would be nice. Certainly, how to refoam, where to get foam, etc. should be pinned, grille cloth discussions, etc. etc. I'm having trouble finding my own threads, LOL!

Hi Carl, My friend is not Andy K., he wishes to remain anonymous. I'll ask him next time we exchange e-mail.

Hi Doug, Yes I'm sure, I'm surprised that they made the mistake of going to the 16/16 version, but not so surprised that they went back. My friend is very methodical so I have a lot of confidence in his schematic, but who knows how many were shipped with that. He said himself that the later design(s) was the high volume seller, what we've called Rev1 (16/16) and 2 (later 16/8). The very thin wire inductors in Rev 0 and 1 were also a mistake, IMO.

My friend sent me a schematic from his personal files, he says that he drew it since he owned a pair of the Advents from that time and it is dated 26 August 1970. My friend wrote: "The date would place it at 377 Putnam Ave., which was the original location of the company and where I started working for them. Don't know which value of L1 and L2 they finally settled on." So this indicates that he did start in 1970. It is earlier than anything we've been talking about here, one member mentioned a very early version with a 4 ohm resistor and this should be it. It is what I've called Rev0, and it has a 16 uF main cap, with an 8 uF extended cap. The resistor is listed as 4.14 ohms. The inductors are listed below: L1 .149 mH, .208 mH, Q=1.6, R=.56 ohms Decrease inductor L2 .850 mH, 1.055 mH, Q=2.0, R=2.5 ohms Tweeter shunt inductor L3 1.42 mH, Q=14 @ 1 kHz, R=.273 ohms Woofer inductor Note that there are two values for L1 and L2 and he states that he's not sure which value they settled on.

Hi Doug, Nice to hear from you!

My friend also spoke very highly of Andy K. and I don't think there is any disagreement, he did say that Andy K. fine tuned the voicing on most of the early Advents. I am completely of Greek heritage and people like Andy Kotsatos, I'm sure, make all Greeks feel proud. I don't think I'll return to my family's original name though.

Hi Vern, Thanks for your comments. Thinking about this more, my friend says he arrived there in the early 70s, which could be 1972-73, when the revision from the Rev1 to Rev2 crossover was done. I would agree that something doesn't sound right especially in the extended position with the Rev1 design, however, I don't recall any changes in the tweeter from Rev1 to Rev2. There was the tweeter grille and use of bulb dye from the very early to Rev1 change, so I think more likely this was it. Perhaps, I'll send him the email from Andy Kotsatos where he mentions the bulb dye on the tweeter is mentioned. My friend also mentioned during our conversation that an MIT grad student did most of the Small Advent work, again with Henry's input and oversight. Really, it is just a box reduction, and new woofer.

I worked over 10 years ago with an analog engineer who had previously worked at Advent in the early 1970s. We often had lunch together where we chatted about what went on behind the scenes. I ran into this friend coming out of the Grand Hyatt in NYC recently when the HE 2007 show was going on. I have to say that I was surprised to read on this forum that some believe that Andy Kotsatos designed all the Large Advents. The early Large Advents have the writing on the back "Designed By Henry Kloss" and I believe it. I posed this question to my friend when I ran into him, and this was his response in a later email, posted with his permission: ================================================================= "Regarding your Advent query - the way I remember it happening was that Henry Kloss had a noncompete clause when he left KLH that prevented him from peddling loudspeakers for some specified period of time. According to legend, he designed the Advent loudspeaker and filled a couple of trucks with the things. On the day that the noncompete clause expired, the trucks rolled out to the stores! It is entirely possible that these very first loudspeakers were entirely of Henry's design." "By the time I arrived at Advent R&D in the early 70's, I vaguely remember there being some brouha about the loudspeaker not sounding right. One of my first tasks was learning how to run the General Radio stripchart equipment, and I wound up running lots of loudspeaker and crossover curves. Bruce Gregory, the lead electrical design engineer, wound up redesigning the crossover and Andy did the voicing by tweaking the parameters. There was a lot of back-and-forth (and lots of curves) getting the thing right. They also made a design change to the tweeter, but I don't remember the details. If anyone has an early Advent Utility, most likely it is one of these revised units, since they were the ones that sold in volume." "Personnel involved with auditioning the Advent loudspeaker product line most likely were Andy, Bruce, Henry, Stan Pressman (head of marketing), and Joe Hull." ================================================================= Comment: We have only identified 2 early versions of the Large Advent what I call the Rev1 16/16 uF, and the Rev2 16/8 uF, what I call Rev3 is the New Advent. The Rev1 that I worked on was from 1972, and I have seen a very early version without the metal mesh screen over the tweeter. This earlier version might also have the crossover that was "not sounding right". There is also the addition of bulb dye to the tweeters to seal the sometimes porous paper cone. I have never seen a natural paper color Advent tweeter but they probably exist. The Rev1 and Rev2 versions are the ones that sold in large volumes.

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 for the Dyna A-25s 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. Moderators can you pin this thread since it is such a common question?

Grille Cloth link

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.

Would someone with original Dyna A-25 Grilles please count the thread count per inch? I have A-25s but the grilles were missing. This would help to find a good replacement material.

Aperiodic Vent link, see previous post.

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?

>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

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?

Some here ask about the large Advent sounding harsh: The peaking in the dotted lined response starting at 500 Hz, peaking at 1.2 kHz, continuing to 5 kHz is one reason for harshness in the Advent sound. BSC helps to correct the response below 500 Hz, and combined with tweeter level adjustment makes a significant improvement in improving the FR balance.

>So here's the scoop, Pete. >The woofers in my 5102s are like Ed's, with a raised >backplate. >Front and back plates are 1/4". >Magnet is 5/8" thick. >There's a pair of 5012s on eBay now at $100 + shipping from >NY. > >What's the big deal about a raised/bumped backplate? Allows >longer cone excursion? Is the second question good enough for >another laugh? Hi Russ, Oh, Interesting, it is different then. Original: 3/8" plates 3/4" magnet 5012: 1/4" plates 5/8" magnet I could enter the numbers in the spread sheet that I have, but we'd need to know the voice coil length. Don't know if the kept the 5/8" length, another common one is 3/4" for these old long throw woofers. But we won't know without looking at one. Anyone have a blown 5012 woofer? Yes Russ the raised back plate allows the VC to move further back before making the loud crack sound as it hits the plate. We should probably start a new thread about the 5012 woofer. Thanks Russ,

I think your joking but, your comment did give me a laugh! Here's a picture of Ed's 5012 raised or bumped back plate: http://www.classicspeakerpages.net/dc/user_files/1543.jpg Here's the thread where we discussed it: http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#1336 I would be very interested to know the back plate, front plate, and magnet thickness. 1/4" plates are very common, however the original and New LA woofers had 3/8" plates. I'm curious about the 5012 woofer if you happen to take a look. Thanks very much for the offer about the crossover, but I bought a pair of 5012 XOs on ebay just for curiosity sake. There's a 7 uF from the + input to the fuse. Other end of fuse has an inductor to ground (fairly large air core), also a 32uF to a 3 ohm resistor, other end of resistor to tweeter +. Woofer has a not so large air core inductor in series with the + lead, wired with positive polarity. Best Regards! Pete B. >Pete—you know enough about me to know that I don't know what >a backplate is. But if you tell me, I'll take the woofer out >and try to find it. If it's big enough, I just might have >lunch on it tomorrow, and even outside, if the sun shines. > >I have these 5012s just sitting idle. I don't want to put them >on eBay because they never bring what they're worth. And >they're quite good. The cabinets are just a little larger than >the original Advent Loudspeaker, the x-over is different, >there's no tweeter level control, and the tweeters haev fuse >protection (which I have disabled). > >While I'm inside, I'll examine the x-over and note the details >for you, so you'll have something else to think about this >week ;-)

Hi Russ, Interesting comments regarding your comparision of the 5012 to the LA. Do you happen to know if the 5012 woofer has a raised backplate? We discussed this in another thread as you might have noticed. It might be slightly better than the New LA woofer, mainly when pushed hard. I'd like to hear those 5012W's I'm curious now. Best regards, Pete B. >Hello, gks. > >I have a pair of 5012W's, made during the Jensen years. To me, >they sound exactly like the Advent Loudspeaker, though the >x-overs are different and the cabinets are slightly larger in >every dimension—about 1/2 inch. > >They never seem to draw much interest on eBay, and rarely come >up there. So I have this very nice pair, in very nice >condition, with new poly caps and pretty fresh woofer >surrounds, and I'm wondering what to do with them (since I >already have 4 Advents in a double system and two very lovely >Smaller Advents I recovered in white birch veneer and >refurbished with new tweeters and x-over components—AND >resting securely on beautiful stands I made myself). > >If you have the answer to THAT, you most certainly ARE and >expert, because anyone who knows what action I should take has >to be an expert. I am expert at many things, but knowing what >to do is not usually one of them ;-). > >Your original post was engaging. > >Best wishes. > >Russ Wollman > >

AR claimed 97 dB/2.83V/1m for these speakers and given the relatively typical box volume used I thought they must not have deep bass, or they will not make the efficiency rating. You cannot beat the bandwidth/volume/efficiency tradeoff as predicted by Thiele and Small theory. Sure enough the frequency response curve shows that the system produces an average of about 94 dB from about 150 Hz to 9 kHz. It is possible to make relatively efficient midranges and tweeters. The response steps down to an average of about 89 dB from about 120 Hz to 80 Hz, and it is down a significant 14 dB at 40 Hz and about 7 dB at 50 Hz. An interesting comparison is to the Large Advent which is down about 1 dB in the low 40s, ignoring baffle step losses. It is clear that the woofer is fairly typical with a sensitivity of about 89 dB in the passband. The modification that I've suggested pads the mid/tweeter section down by about 6 dB and since the problem is differing efficiencies, it should provide a good correction from the start of the woofer passband at 80 Hz on up into the tweeter range. There is a 5 dB dip in the frequency response at about 12 kHz which probably explains the lack of air. Keele also notes that the left system was down 5.5 dB at 10.6 k compared to the right and -4dB at 18.1 kHz. I wonder if there is a consistency problem with these tweeters. The vent seems to be tuned to 30 Hz and there is a layer of fabric in the port to lower the Q. This is generally considered to be a bad idea, and indeed Keele noted that the fabric added significant distortion flapping, with high output in the deep bass. Keele notes that the woofer is robust and handles a lot of power without a problem. I also found them to handle significant power without strain. I expect that the 310HO will be even worse as far as deep bass goes having a 10" woofer. I plan to measure and simulate, when I have the time.