inside the Bozak 300a

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Comments

  • rednedtugentrednedtugent Posts: 9,878
    ulya3lrunx0h.jpg
    second picture didn't post... second try.
    Thinking minor mods.
  • msgmsg Posts: 2,867
    I was just going to ask to see the rest.
    Are they intact?
    Are you doing any work on them?
    How do they sound?
    Did you know you have on one blue sock and one black?
  • rednedtugentrednedtugent Posts: 9,878
    msg wrote: »
    I was just going to ask to see the rest.
    Are they intact?
    One single. I lost out on the concert grand and this is what
    was left. I believe a doctor owned it.

    Are you doing any work on them?
    The first easy thing to do is move the resistance up to 16 ohm.
    The Mid kind of runs wide open and overlaps the tweeters.
    I'll follow the advice of the Bozak experts on the web and go slow
    and see how it turns out. I don't have any room in the studio for this
    thing.

    How do they sound?
    The tweeters are too harsh for me. I didn't notice it when I was
    using it as a center channel. (audyssey)
    The bass and mid-bass is real nice.

    Did you know you have on one blue sock and one black?
    I've done that, but no. White today as I am wearing water proof shoes.
  • rednedtugentrednedtugent Posts: 9,878
    first surprise, the xover is not screwed in place. Just sitting there.
    ez6wv1cvyza5.jpg
  • rednedtugentrednedtugent Posts: 9,878
    Second surprise, this was behind it;
    s0zzasbl56b1.jpg
    It reads
    Mallory
    4 MDF 50 VDC
    ca 275
    9-52
  • rednedtugentrednedtugent Posts: 9,878
    Next I'll take the sage advice of Pat Tobin;
    "Here's what works best to curtail that upper end doubling: On the N-10102A xover, at terminal strip A, move the jumper from the N-101/N-104 terminal to the other one, marked N-102. That doubles the inductance feeding the midrange, which happens to lower the drive to the midrange in the 2.5 kHz ~ 10 kHz range, exactly what we need. (For technocrats: that inductance was used for an 800 Hz rolloff for the 16-ohm B-305 midrange.)"
  • rednedtugentrednedtugent Posts: 9,878
    edited May 1
    Time for some redbook Mono recordings. First up;
    29ga50av6mb8.jpeg
  • SchurkeySchurkey Posts: 1,660
    In my house, the amp would be connected to the binding posts with 12-gauge wire...




    ...and then the drivers are hooked-up with doorbell wire inside the cabinet.

    What's the ESR and capacitance of that '52 Mallory?
  • rednedtugentrednedtugent Posts: 9,878
    funny you should mention rewiring as I was thinking about that...
  • rednedtugentrednedtugent Posts: 9,878
    Another must Mod suggestion was replacing the mid range inductor and
    I'll be giving that a shot.
  • rednedtugentrednedtugent Posts: 9,878
    listening to DDC Japan Pet Sounds now...
    It sounds pleasing if it isn't pushed to hard.
    Some frequencies just fall apart turned up.
    There is a bit of warm hollowness to the sound.
    Great midrange detail after the simple change!
  • rednedtugentrednedtugent Posts: 9,878
    any links to these suggestions? I was hunting around for solid core wiring
    but no winner.
    Schurkey wrote: »
    In my house, the amp would be connected to the binding posts with 12-gauge wire...
    ...and then the drivers are hooked-up with doorbell wire inside the cabinet.
    What's the ESR and capacitance of that '52 Mallory?

  • rednedtugentrednedtugent Posts: 9,878
    o.k. so I finally placed a parts-express order two days ago.
    I've three "projects" going.

    picking sheet excerpt
    266-350 ERSE 1.0mH 14 AWG Perfect Layer Inductor Crossover Coil
    260-302 Gold Plated banana 5-way

    I was able to install the Inductor and the modest parts express gold plated 5 way banana posts this morning.

    Once again I'm listening to DDC Japan Pet Sounds at low levels.
    Running this thru the Denon AVR-4520ci and it sounds real nice
    up thru 40% to 60% power. It starts to get boomy up there. One wonders what a
    nice tube amp would do for it...
  • SchurkeySchurkey Posts: 1,660
    edited May 6
    Schurkey wrote: »
    In my house, the amp would be connected to the binding posts with 12-gauge wire...
    ...and then the drivers are hooked-up with doorbell wire inside the cabinet.
    any links to these suggestions? I was hunting around for solid core wiring but no winner.
    I bought a spool of a couple hundred of feet of "Military Surplus" 12-gauge stranded silver-plated copper wire with Teflon insulation for in-cabinet wiring harnesses. The stuff is available on eBay in various lengths and gauge sizes. Beware of "spools" made from multiple shorter lengths of wire stripped from old aircraft vs. leftover spools of continuous-length wire. Small-gauge wire seems to be exceedingly common, 12-gauge less so. I don't think any of this is solid-core wire.

    OTOH, you can simply drive to any home-improvement store on Earth (Home Despot, Lowe's, Menards, etc.) and pick up some solid core--or stranded core, your choice--THHN wire in a small variety of colors and gauge sizes. The insulation is PVC with an outer jacket of somethig else--oil, gasoline, and moisture resistant, slippery, and sturdy enough to accept some abrasion as the wire gets pulled through conduit (which of course is of no value in this application.) although it tends to be a "hard" plastic. You could go to any automotive parts store (NAPA, Advance, NaughtyZone, Pep Boys, or whatever) and get automotive "Primary Wire" in a color and gauge size pleasing to you, which will have a polyethylene insulation that's a bit more flexible. I don't think the flexibility is a particular advantage in this application. The automotive wire will be stranded. I'd use stranded THHN if I wasn't using my Military Teflon. The point being you have access to reasonable gauge, solid or stranded copper wire of low cost and adequate specification, although it's not going to be considered "audiophile approved".

    Schurkey wrote: »
    What's the ESR and capacitance of that '52 Mallory?
    Are you able to test them, or are you simply replacing 'em?.

    I would dump them if they couldn't be tested for ESR/dissapation, and capacitance.
  • littlewoodboatslittlewoodboats Posts: 791
    I would not just dump those caps. The good Doc Hardy pointed out in another thread certain caps of that type are highly prized. Even if you replace them do a bit of research to figure out what you have. Maybe Mark will see this and comment.

    I think would be well worth the effort to have them checked but could be wrong.

    When set up well I enjoy listening to old Bozak's. Cool project. I would love to run across a pair of CG's and would buy them even knowing there would be a 50/50 chance my wife would shoot me for doing it.
  • rednedtugentrednedtugent Posts: 9,878
    I don't think I'll replace the caps. I don't want to change the flavor too much.
    The wiring OTOH needs replacing for sure.

    As it stands now I can at least listen to it. Before I started, not so much.
    Gives me time to ponder the next move.
  • SchurkeySchurkey Posts: 1,660
    Do I understand the stamping on the capacitor? They were made in 1952?
  • rednedtugentrednedtugent Posts: 9,878
    edited May 6
    Seems so. A little early for this speaker I believe. I need to look into it.
  • rednedtugentrednedtugent Posts: 9,878
    o.k. so I replaced the wiring to the drivers.
    I did the second Tobin mod suggestion of moving the
    woofer leadwire to the upper N-102/104 tap.
    Things are coming into focus.
  • rednedtugentrednedtugent Posts: 9,878
    In reading threads from Mr. Tobin I discovered the blanket over the Xover
    was really a curtain that hung a little over 1/2 way back in the cabinet.
    He HIGHLY recommended putting that in place. Well, the old one is disintegrating
    so I made one.
    no522g7725h9.jpg


  • rednedtugentrednedtugent Posts: 9,878
    At lower volumes this speaker really shows its potential.
    I fear a Xover rebuild is the next and final step to make her really sing.
    I guess protecting the drivers is good enought reason.
  • rednedtugentrednedtugent Posts: 9,878
    so I popped open the hood on the med/tweeter crossover.
    Caps made in Chicago;
    8k7la6j1xfaf.jpg
  • rednedtugentrednedtugent Posts: 9,878
    Doesn't look to easy to get those out. :#
    In looking at the cap config I sumised that if I made one well placed snip,
    the old 5 MFD tweeter caps would be out of the circuit...

    ...I ran it with the tweets disconnected and it was obvious that the balance
    was off between the woofer/mid vs the tweeters.

    Next I placed a couple of Solens 5.1 caps in parallel (for another project but handy)
    with a .5 ohm mills resistor in front. Buttoned it up and sound check....
    sounds the same as before I started! The tweets are too hot as before.

    Well Mr. Tobin knew all that and suggested a resistor that is now on order
    from parts express. I went ahead and ordered ONE
    Dayton Audio DMPC-50 50uF 250V Polypropylene Capacitor
    to replace all the other mid capacitors.


  • rednedtugentrednedtugent Posts: 9,878
    after breaking a dayton 7.5 resistor :#
    I received a new parts Xpress order and now the tobin mods are done.
    1v5wb7la0rrg.jpg
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