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Bozak Mystery

Steve Smiley said:
Thanks to @drbiggles for suggesting to get the backs off those things, as it goes a long way in providing you direction for action.

It looks to me like you have Bozak B-305 components in your speakers, as opposed to the Symphony components. If that is an accurate guess, the mid is probably a 16 ohm mid. I'm not very familiar with the B-305 crossover network, but the info is readily available.

The boxy thing is an enclosure that actually contains the capacitors. The doughnuts are the inductors. The inductors are good, the caps you will want to replace.

The fiberglass insulation is something you will want to replace with cotton batting. I know people have found a source for the batting but I haven't seen it posted. Hopefully someone can chime in. You will not get the performance you want with the infinite baffle design (that's Bozak) without the appropriate batting. You will also want to add the flower pot over the mid. When I get a chance, I can share a link to the Home Depot version to give you an idea.

You can replace all four of the B-200x with four B-200y for the same layout on your baffle.. Those are most likely set up on a series/parallel configuration so that it shows as a 16 ohm load...heck, you can just use one of them for that matter. A B-200y single is a 16 ohm load.

I would recommend you become an AK subscriber and then you can post a WTB for parts. It's only $25 for the year and a good resource. There is also a few online marketplaces. You should also join the Facebook Bozak group. There is good info and help there, knowledge and possible parts.
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I was going to replace the 4 B-200x tweeters with a single B-200y as you suggested. But then I decided to wait until after I replaced the capacitors, replaced the lining and installed a swinging curtain. After I've done that I will listen to some music and see how I like the speakers first. I may be satisfied with them without replacing the tweeters. But if I'm not, are you sure that one B-200y is 16 ohms? Someone else told me that the B-200y is 4 ohms, and that I'd need four of them to equal 16 ohms.
 
Yup, we're sure sure the B200Y tweeters are 16ohms. Remember, were dealing with 70+ year old technology. 16ohms was the norm back then. Today? 4 ohm tweeters are more popular.

Biggles
 
drbiggles said:
Yup, we're sure sure the B200Y tweeters are 16ohms. Remember, were dealing with 70+ year old technology. 16ohms was the norm back then. Today? 4 ohm tweeters are more popular.

Biggles
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Thanks Dr. B. Can you explain the scrim to me? Like what material I could use and where I should put it.
 
Scrim is simply any substrate material that can be used to glue the cotton batting onto. If you go to Google and type in what is scrim, there’s a YouTube video that shows you how to glue cotton batting onto scrim. Or just use Google images, it shows you.

You need scrim to hold the cotton batting together to make the swinging curtain. If you pull out the cotton batting, it’s flimsy as hell. You’re going to have to work to figure out how to get your cabinets lined and that curtain made. You’ll need at least one can of 3M 77 spray adhesive.

Once you get the cotton in your hands, it should all start to make sense.

Biggles
 
Retrovert said:
Here is what I elsewhere wrote (slightly edited to remove extraneous material and for clarity) two years ago on the subject of Tufflex.

That yellow material is Tufflex, a reprocessed cellulose (industry names viscose or rayon), praised be its name.
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Whatever they did to the cellulose in Tufflex, it's orders of magnitude more stable than the cellulose fibers in Kimsul.

Cellulose fibers are made from wood pulp reprocessed in many steps to form long chains, i.e. a polymer, so they are mostly identical across the structure. The greater the crosslinking (polymerization) the greater the strength of the resulting fiber. Rayon is a tradename for a processed cellulose. The FTC forced manufacturers to stop calling cellulose from bamboo "regenerated fibers".​
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If someone had a sense of humor, they should have started calling it "Gallifreyan Cotton."

Tufflex was a reprocessed cellulose fiber — variable source material, including plant fibers like cotton or cellulose derived from trees — designed in the 1950s and sold throughout the 1950s and 1960s to compete with cotton for padding in furniture and acoustic deadening. The exact properties are not easily discoverable, but we can proceed as if it was similar to that of rayon given the similar raw materials.​
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If there is any way to sort out the properties of Tufflex, I have a stack of it in my basement that came out of my 1970 or 1971 (very early B200Yc tweeters and B199Ac woofers) B301 tempos when I gutted them for parts to start rebuilding my 1958/59 B302As. That should date from the very end of Tufflex production.

Kimsul, the earliest material used by Bozak, is the earlier Kimpak insulation — one inch of cellulose fibers between sheets of kraft paper — with an additional asphalt coating to reduce the otherwise considerable flammability. (Kraft is the German word for "strong".) The paper was required for strength, as the cellulose fibers were quite weak. Kimsul was created by Kimberly Clark in the 1930s. Other similar products were called "balsam wool". Flammability is greater than for cellulose (above described) alone.​
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Just as a clarification, Bozak either used Kimsul and Tufflex side-by-side or went back and forth due to cost or supply concerns. My 1958/9 B302As, which were unmolested when I rebuilt them, had Tufflex lining. On the other hand, my 1960 or 61 CGs have Kimsul around the tweeter array.

drbiggles said:
Yup, we're sure sure the B200Y tweeters are 16ohms. Remember, were dealing with 70+ year old technology. 16ohms was the norm back then. Today? 4 ohm tweeters are more popular.

Biggles
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Well, Bozak did tend to run them in pairs or arrays to bring everything down to 8 ohms. He was an early adopter of accurate* 8 ohm ratings.

(*JBL was notorious for misrating their drivers, calling what should have been a 4 ohm driver an 8 ohm driver, a properly 8 ohm driver a 16 ohm driver, and the weird JBL/Dukane 15" 130/140 series drivers that I have that are marked 32 ohms actually seem to measure out at what anyone else would have called 16 ohms.)

drbiggles said:
You’re going to have to work to figure out how to get your cabinets lined and that curtain made. You’ll need at least one can of 3M 77 spray adhesive.
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A staple gun is always the traditional method.
 
The cotton upholstery batting is too loose for a staple gun. I did use squares of cardboard and staples for a while, but even that was questionable. But cotton is a natural product. If this or any other batch seems to hold together alright, feel free to use staples.

Biggles
 
Sam Cogley said:
(*JBL was notorious for misrating their drivers, calling what should have been a 4 ohm driver an 8 ohm driver, a properly 8 ohm driver a 16 ohm driver, and the weird JBL/Dukane 15" 130/140 series drivers that I have that are marked 32 ohms actually seem to measure out at what anyone else would have called 16 ohms.)


.
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Well, it wasn't a much a mis-rating- as a reflection of the behavior of the driver, in the enclosure (frequently horns)- especially drivers with huge magnets- which due to back EMF, made the driver act like a higher impedance. In these cases- a "nominally" 4 ohm driver could have an effective impedance significantly higher than 4 ohms. The rating JBL used, frequently reflected the effective power delivered to the driver from an amp, that would result from the impedance on the driver. It won't "jibe" with the DC resistance- but it will reflect the effective AC impedance in use, in many cases...

Regards,
Gordon.
 
GordonW said:
Well, it wasn't a much a mis-rating- as a reflection of the behavior of the driver, in the enclosure (frequently horns)- especially drivers with huge magnets- which due to back EMF, made the driver act like a higher impedance. In these cases- a "nominally" 4 ohm driver could have an effective impedance significantly higher than 4 ohms. The rating JBL used, frequently reflected the effective power delivered to the driver from an amp, that would result from the impedance on the driver. It won't "jibe" with the DC resistance- but it will reflect the effective AC impedance in use, in many cases...

Regards,
Gordon.
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Gordon,
A long time back, I read multiple posts from Harvey Gerst (who was at JBL at the time, and was responsible for the design of the "F" series MI drivers inspired by Fender) and Zilch (who measured damned near every speaker in sight) which said that JBL played "fast and loose" with their impedance ratings (Zilch) or "we lied" (Harvey).

Harvey Gerst on 1950s/60s JBL impedance ratings:
Simple answer:

Back then, we lied.

Even though they're marked as 16 Ohms, they were all really 8 Ohm speakers. The DC resistance should be around 70% of the nominal rated impedance, so an 8 Ohm speaker should read about 6 Ohms (or so) DC. Ignore the 16 Ohm decal; it was really an 8 Ohm speaker.
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https://www.audioheritage.org/vbull...-cone-question&p=327975&viewfull=1#post327975

YMMV.
 
Sam Cogley said:
Gordon,
A long time back, I read multiple posts from Harvey Gerst (who was at JBL at the time, and was responsible for the design of the "F" series MI drivers inspired by Fender) and Zilch (who measured damned near every speaker in sight) which said that JBL played "fast and loose" with their impedance ratings (Zilch) or "we lied" (Harvey).

Harvey Gerst on 1950s/60s JBL impedance ratings:

https://www.audioheritage.org/vbull...-cone-question&p=327975&viewfull=1#post327975

YMMV.
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That's true in a front-loaded cabinet.

However, in the very early days- when most drivers were used in theater systems- almost all cabinet were horns. These are where the impedance was closer to "spec".

JBL just never updated their impedance rating methods, until MUCH later. In the days of the SFG (ceramic magnet) woofers and beyond (mid 1970s roughly), the impedance of the drivers very much closer matched everyone else's ratings... a 2225J typically has a DCR of about 12 ohms, for example...

Regards,
Gordonn.
 
GordonW said:
That's true in a front-loaded cabinet.

However, in the very early days- when most drivers were used in theater systems- almost all cabinet were horns. These are where the impedance was closer to "spec".

JBL just never updated their impedance rating methods, until MUCH later. In the days of the SFG (ceramic magnet) woofers and beyond (mid 1970s roughly), the impedance of the drivers very much closer matched everyone else's ratings... a 2225J typically has a DCR of about 12 ohms, for example...

Regards,
Gordonn.
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If you read some of Harvey's very entertaining posts, there's a reason why they didn't update their impedance specs for a long time, and it goes back to the post I quoted, and JBL's sound profile reputation.
 
drbiggles said:
The cotton upholstery batting is too loose for a staple gun. I did use squares of cardboard and staples for a while, but even that was questionable. But cotton is a natural product. If this or any other batch seems to hold together alright, feel free to use staples.

Biggles
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Sorry for being late to the party...when I Tobinized my 302A's I used a thin strip of wood and screws to pinch/attach the original batting curtain to the underside of the top of the speaker...Appropriate method? TIA
 
eiraved said:
Almost 4 years late. Welcome back to AK!!
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Thanks...Better late than never <grin>
Also, please don't ban me for saying this, but when I Tobinized, I used jumpers at all connections rather than hard soldering, which would give opportunities to try different configurations...Is that a really bad thing to do? If so, I can always, someday, get back inside, to correct to hard connections
TIA
 
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brian welch said:
Sorry for being late to the party...when I Tobinized my 302A's I used a thin strip of wood and screws to pinch/attach the original batting curtain to the underside of the top of the speaker...Appropriate method? TIA
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I don't see that being any sort of a problem. As long as whatever you use is secure, spreads the load around enough for the curtain to not rip through and come loose, and doesn't take up excess space, it should be fine.

Regards,
Gordon.
 
brian welch said:
Thanks...Better late than never <grin>
Also, please don't ban me for saying this, but when I Tobinized, I used jumpers at all connections rather than hard soldering, which would give opportunities to try different configurations...Is that a really bad thing to do? If so, I can always, someday, get back inside, to correct to hard connections
TIA
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As long as the connections are secure, solid and no chance of coming loose to cause a short? Not a problem.

Biggles
 
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