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The GREEN MONSTER Bozak 929

DENNYDOG

DENNYDOG

Addicted Member
The first time I saw the 929 I thought it looked pretty cool. The big green meters are like nothing else I have seen along with the stealth flat black finish. I offered the seller what I thought was a decent price which he decided to take.

I really don't know the history of the amp other than him saying that it doesn't work. I haven't tried powering it up which I will leave to the tech when the repair it.

It's a really neat amp when you start looking at how it's put together. It must have been designed for ease of repair as it's a modular design. It has four removable amp sections along with what I believe is the driver board. Most everything seems to be plugged together for easy removal.

The amp is in fairly rough condition. No major dents to the case or faceplate and all the fins for the heat sinks are there. Just a ton of scratches everywhere. The faceplate actually doesn't look that bad after a quick cleanup. I might be tempted to leave it as is other than trying to repaint it.

This is what it looked like right out of the box.

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First of all, let me say congrats!! Welcome to the club.

Wonderful design, simply ingenius layout. Again, the result of Bozak and Betts hard work. Direct and clean.

After speaking with Mr. Betts regarding my 919 (which has it's share of sccratches), I learned that the modular design served a few purposes. They originally intended to offer upgrades to the public/corporate accounts. The "plug n play" boards would be easy to replace and work on for their technicians. This same thought was also given in respect to repairs and servicing.

Are you a member of the Bozak group? There is a member there named Judy Ingels. She owns both a 919 and 929, run together in the same system.

Anyhow keep us posted on how the rebuild is going. Who are you getting to do it? Are you aiming for an original spec or something modded a bit. I just saw an original manual and schematic for the 929 on Ebay about a week ago.

OK, found it...http://cgi.ebay.ca/BOZAK-929-Stereo...pt=Vintage_Electronics_R2&hash=item53e1b1fb21

The schematic will be priceless for a good tech to be able to do a proper job on it. No guessing, all done to spec.

Ciao.
 
Thanks!

Poppa, I saw that auction but had forgotten about it. The copy is a little on the high side but I bought in anyway. This will be a must have for whoever does the work.

I contacted Echowars but haven't gotten a reply yet. I guess he is super busy right now and had heard he wasn't taking any new jobs at the moment. Not sure if this is true or not.

I could see if Hi Fi Sound in Minneapolis would work on it which in that case I wouldn't have to ship it. I don't know if they would be up for doing a complete rebuild on it though. I have heard they are picky about what they work on and will turn down things they don't feel are worthy. Not sure if this is true or not.

I did register as a member on the Yahoo user group right after I bought the amp. I saw your postings about the 919. Their layout is a little confusing. I wasn't able to find any info on the 929. I found this to be the case searching on the net also.

There was an auction for a CMA-2-150 amp that just ended. This is the commercial version of the 929. I would have liked to bid on it but didn't want to spend the $185 he was asking along with the $60 or so he wanted for shipping. It's basically the same amp except it's rack mountable with a silver face plate and no power meters along with XLR inputs and a removable power cord.

I'm excited about getting this thing going. I would like to use this in my shop paired to a pair of B-302A Urbans I got from MJarve.
 
Saw this after I replied to your PM. Yes, I'm busy, and haven't been on AK too much the last few weeks. Sorry about that.

Looks like it uses a couple of tube buffers at the input. Weird design, for sure.

Grab the schematic while you can. Hopefully it'll give you (or the next tech) some voltages to measure.
 
PM replied to. Got the sm ordered for it. We will see if I can do anything myself with it. I'm no tech by any means.

Denny
 
DENNYDOG said:
The first time I saw the 929 I thought it looked pretty cool. The big green meters are like nothing else I have seen along with the stealth flat black finish. I offered the seller what I thought was a decent price which he decided to take.

I really don't know the history of the amp other than him saying that it doesn't work. I haven't tried powering it up which I will leave to the tech when the repair it.

It's a really neat amp when you start looking at how it's put together. It must have been designed for ease of repair as it's a modular design. It has four removable amp sections along with what I believe is the driver board. Most everything seems to be plugged together for easy removal.

The amp is in fairly rough condition. No major dents to the case or faceplate and all the fins for the heat sinks are there. Just a ton of scratches everywhere. The faceplate actually doesn't look that bad after a quick cleanup. I might be tempted to leave it as is other than trying to repaint it.
This is what it looked like right out of the box.
Click to expand...


Its in better condition than a Dynaco I worked on for a guy awhile back.
At least with this one it appears to have everything with it.
As EW mentioned you're definitely going to need service data for it.
 
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DENNYDOG said:
PM replied to. Got the sm ordered for it. We will see if I can do anything myself with it. I'm no tech by any means.

Denny
Click to expand...

Denny, if that sm indicates what the tube sockets are for, I'd love to know. The layout of your 929 seems to be identical to my 939, except the 929 has more output transistors(?) for more output. Your caps are probably larger as well. 120wpc vs my 70.
 
I remember reading somewhere that there isn't anything that is normally plugged into them. Test sockets maybe? I should get the service manual sometime this week.

Here is a link to a few more pictures and bigger ones from the first post. I took some closeups of the output transistors too.
 
I thought I would post this. It's the front page of the 929 manual. I could just make it out from the picture they had on the auction.

It gives some insight as to what the octal sockets are for along with descriptions on the design and operation of the amp.

TEMPORARY INSTALLATION & OPERATION MANUAL FOR BOZAK MODELS 929 AND 929PV TWO-CHANNEL AUDIO POWER AMPLIFIER

(NOTE: This temporary manual is being furnished to you in order that you may begin to enjoy the use of your Model 929 amplifier while the permanent manual is being prepared. Congratulations on being one of the very first owners of this outstanding component for home music systems! A copy of the permanent installation and operation manual will be sent to you, provided your warranty card is returned, when printing is completed).

The Bozak Model 929 is a relatively high-powered amplifier intended for very demanding applications in the reproduction of sound. Model 929PV is identical in every respect to Model 929, except that the power-level meters and associated circuitry are not included.

Its design utilizes the most advanced circuitry and components available at the present state of the art. Modular design, a newly developed series output configuration and a triple protective circuit combine to assure the greatest possible reliability from a modern transistorized design.

The two channels are capable of delivering their full rated 150-watt RMS power simultaneously and continuously into 8-ohm loads from 20Hz-20kHz at less than 0.2% total harmonic distortion.

The circuitry for the two amplifier channels and for the protection circuit are on one plug-in printed circuit board. The output transistors are mounted on the individual extruded aluminum heat sinks with plug-in connectors to the main mother board.

The direct-coupled output stage is electronically protected against over-heat, short-circuits and overloads--there are no fuses in the output circuit. Should any of these faults occur in either channel, a relay circuit automatically disconnects the loads from both channels and an indicator light signals the fault.

Octal sockets are provided for plug-in type balanced-line input transformers or for high-pass and low-pass filters for bi-amplification, in which case a plug-in power supply is also required.
Click to expand...

I thought I would post a picture of what the amp looks like when it's powered on. Its borrowed from Ebay member rebaccaannray who sells the manual. I think you can see why I call it the GREEN MONSTER.

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Very sexy, those meters are way cool. I like the sleek look of the faceplate.
That modular construction looks like it would be easier to work on the boards.
 
That's a cool looking amp, can't say I've ever seen one before. 150WPC into 8 ohms, can it double down into 4 ohms? How much does that beast weigh?
 
I am guessing it weighs around 45-50 lbs. It has pretty decent heft to it for just a power amp without the preamp section.

As far as the power output into 4ohms I won't find out until I get the manual. If it even states what it would be.

I should be able to figure out if I can fix it myself with a little help and the manual. I'm pretty limited in my electronics knowledge so I'm crossing my fingers it's something simple.
 
The part count on each of those output boards looks low. Since you can breakout each board individually, it should be fairly easy to restore.
Finding the cause of why it doesn't work would precede restoration, in my little world.
 
The plan is to get it working first. Then a possible restoration. If I am up to doing either. :stupid:
 
DENNYDOG said:
The plan is to get it working first. Then a possible restoration. If I am up to doing either. :stupid:
Click to expand...

With a unit like this you're going to need to go through it thoroughly
to get it running properly. If you attempt to merely patch it up make
sure you keep plenty of this on hand....

advil_small.jpg



....because the unit will give you headaches.
 
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