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Problem With Bozak Concert Grand Tweeters Help!!

Mc_Man

Mc_Man

Well-Known Member
So just this weekend I picked up and set of very nice circa 1972 Bozak Concert Grands. The odd thing is I get get no tweeter from either speaker. I have tried different sources, amps, and cables. Both mids in each cabinet work as well as all 4 woofers. I have opened one up, quite a chore, and don't see any broken or damaged wiring connected to any of the tweeters. There is what looks to be some oxidation build up on some of the tweeter terminals but not enough to say it would be problematic. I have snapped several pics of the crossover hoping this is where my problem lies. I just find it hard to believe every fricken tweeter in them are dead (8 per speaker no less). Any help would be greatly appreciated.

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If all the tweeters are not operating, its probably something in the circuit -- bad capacitors most likely, but maybe either broken wires or a connection not being made. I believe they were biampable, and maybe the previous owner was using them is some way that bypasses the standard hook up.
Nice score, by the way.
There is an active Bozak user's group, and they might be able to give more detailed suggestions.
 
I seriously doubt if all the tweeters have open voice coils. So, I'd suspect crossover problems. First, using a volt-ohm meter, check the drivers for any opens. Then, if your meter can check capacitance, check the caps on the crossover. These will need to be removed from the circuit to get an accurate reading. Good, non-polarized caps are readily available.
 
Hopefully it's only a crossover problem, as aluminum cone Bozak's aren't exactly cheap. I find the best way to test driver's is unwiring them and hooking to a running music source to give them a listen. If they don't play or have rubbing voice coils you'll notice it. Use inline capacitor's for tweeter testing.
 
The user group mentioned is on Yahoo.

Congrates on the Concert Grands, well worth the effort I hear.
 
Ok so before I start cutting wires or melting solder I took my meter and tested the ohm resistance on all the tweeters. I get a reading of around 5.3 on all the tweeters. So are these readings of any use since everything is still in the same circuit?
 
If it's a second order crossover ( 12 dB/octave ie: it has a capacitor in series with the tweeters and an inductor, or coil across the the terminals) check to see if the inductor looks melted or has a burned smell to it. This often results in loss of high frequencies even though the tweeters are intact. If you have access to an impedance full frequency sweep, this will be confirmed by a very low impedance in the treble region, usually around 1 or 2 ohms.
 
Wow, those are in beautiful shape (The drivers look like new). I sure hope you have a good-sized room for them. They're amazing speakers. It's been a LONG time since I last heard a pair. Gloriously-dynamic sound. Life-changing sound.

Those cabinets look like a couple of full-size armoirs rather than speakers. I love the double-doors with the keyholes. Plus, you don't have to worry about a cat burglar climbing through a window at night and stealing those - You need a moving company for those things. Nice score.

Once you've got the tweeter problem in hand (hopefully), I would love to see some more pics (Those doors open, right?). Those are in excellent shape (I haven't seen any that weren't, actually). It must have cost a fortune to transport them.
 
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Concert Grands

I own a set of Concert Grands, before that, a pair of Symphony 1's. Both sets of speakers had the same issue; the caps in the crossover had changed value DRAMATICLLY! Before I changed the caps, I checked every driver in the cabinets, all drivers were perfect. Your problem could be that the caps have opened, hence no signal passing. I cannot tell you how much better the speakers sounded after the caps were changed, truly night and day. Good luck!
 
crowatti said:
I own a set of Concert Grands, before that, a pair of Symphony 1's. Both sets of speakers had the same issue; the caps in the crossover had changed value DRAMATICLLY! Before I changed the caps, I checked every driver in the cabinets, all drivers were perfect. Your problem could be that the caps have opened, hence no signal passing. I cannot tell you how much better the speakers sounded after the caps were changed, truly night and day. Good luck!
Click to expand...

Did you tobinize them, or just do a recap of the original values?
 
I spy...

...........at least two terminals with no solder. In the second pic of the drivers,the short gray and yellow wires on the top posts are looped but not soldered.In pic #4 of the drivers,the short white wire seems to have the same issue,its hard to see because the other wires are in the way.Again I think its looped through the "eye" but not soldered.
I had a pair of Symphonys,IIRC one of mine had the same problem,and it was a loose wire, A.K.A bad soldering job.Inferior soldering was in abundance in my pair. I found no less than 5 "loose" connections. I'd go terminal by terminal and give all the wires a little wiggle. Check all the bi amping terminals / connections as well. I'm bettin' some soldering will bring them back to life.:yes:

Nat said:
If all the tweeters are not operating, its probably something in the circuit -- bad capacitors most likely, but maybe either broken wires or a connection not being made. I believe they were biampable, and maybe the previous owner was using them is some way that bypasses the standard hook up.
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Click to expand...

Ya know I went back and reread this post...the fog is starting to lift a little...:D there was something with the way you had to hook them up.:scratch2:yep now I remember. The back terminals on mine had to have jumpers in place.
There were 4 terminals instead of 2 on each cabinet. Two of those had to be "jumped" together to get the tweets to fire. I don't remember which ones.
 
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Join the Yahoo Bozak group and download the Tobin mod in the files area. Get rid of that old cap box and replace it with the Tobin mod. It not only updates the caps but alters the basic crossover functions for a better listening experience.

With good impedance readings on the tweeters and all of them working, it has to be either the caps are bad or a loose wire somewhere well ahead of the tweeters. In either case DO THE TOBIN MOD! :yes:
 

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