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  1. #1
    Registered user. Seismicpocketwatcher's Avatar
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    Default Bulova Ambassador Automatic 30 jewel

    As a collector of pocketwatches i recently purchased one at auction in the bottom underneath i found a Bulova Ambassador Automatic 30 jewel wristwatch which appeared grotty, i removed the caseback to reveal a very clean and working movement it has Swiss made M5 30 jewel stamped on the movement i have limited knowledge of wristwatches so would appreciate any information you could supply.

    PS The winder and time set work perfrctly but i do not know how to change the date?.

  2. #2

    Default Re: Bulova Ambassador Automatic 30 jewel (RE: Seismicpocketwatcher)

    M5 tells us it was made in 1965 (there might be a similar code on the case, but that could be off by a year or so). I think these are micro-rotor movments, but there should be a code on the bridge of the watch that'll tell us for sure. Something like 12EBAD?

    Most of these would "quickset" the date by moving the time back and forth between 9:00pm or 10:00pm and Midnight.
    My growing collection of "affordable" vintages: http://www.abslomrob.com

  3. #3
    Registered user. Seismicpocketwatcher's Avatar
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    Default Re: Bulova Ambassador Automatic 30 jewel (RE: AbslomRob)

    You are correct the code on the bridge is 12 EBAD.
    Also the rear case has CB 503 M5 does this have any meaning.

    Quote Originally Posted by AbslomRob View Post
    M5 tells us it was made in 1965 (there might be a similar code on the case, but that could be off by a year or so). I think these are micro-rotor movments, but there should be a code on the bridge of the watch that'll tell us for sure. Something like 12EBAD?

    Most of these would "quickset" the date by moving the time back and forth between 9:00pm or 10:00pm and Midnight.

  4. #4

    Default Re: Bulova Ambassador Automatic 30 jewel (RE: Seismicpocketwatcher)

    The M5 on the caseback is also a date code using the same "formula" as the date code on the movment. They started in 1950 with the letter L (not sure why), so L1 was 1951, L2 was 1952, etc. Thus M5 is 1965. Details here.

    Details on the movment (including date quickset description) here.

    The movment was licensed from Buren (who co-developed the micro-rotor design). Micro-rotors suffer from real-estate problems; the rotor is on the same plane as the rest of the watch, which leaves less room for the balance and the mainspring barrel. Effectively, it's a ladies watch movment arranged around the micro rotor, despite being a fairly large 12.5''' watch. A small balance means less accuracy. If you increase the beat rate of the watch to compensate (28,800 would give respectable accuracy), you'd need more power, and since you don't have room for a bigger mainspring, that leads to low power reserve. Both can be compensated for by using higher tolerances in production, which increases the cost.

    This varient chose a fairly low beat rate and good production tolerances, giving it a respectable power reserve.
    My growing collection of "affordable" vintages: http://www.abslomrob.com

  5. #5
    Registered user. Seismicpocketwatcher's Avatar
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    Default Re: Bulova Ambassador Automatic 30 jewel (RE: AbslomRob)

    Thanks for all your help.
    I note that you mention BUREN in your reply, the pocketwatch i purchased was a Buren Grand Prix with the wristwatch tucked underneath how is that for a co incidence.

  6. #6

    Default Re: Bulova Ambassador Automatic 30 jewel (RE: AbslomRob)

    Quote Originally Posted by AbslomRob View Post
    The movment was licensed from Buren (who co-developed the micro-rotor design). Micro-rotors suffer from real-estate problems; the rotor is on the same plane as the rest of the watch, which leaves less room for the balance and the mainspring barrel. Effectively, it's a ladies watch movment arranged around the micro rotor, despite being a fairly large 12.5''' watch. A small balance means less accuracy. If you increase the beat rate of the watch to compensate (28,800 would give respectable accuracy), you'd need more power, and since you don't have room for a bigger mainspring, that leads to low power reserve. Both can be compensated for by using higher tolerances in production, which increases the cost.

    This varient chose a fairly low beat rate and good production tolerances, giving it a respectable power reserve.
    Some comments: The Bulova 12EBAD does not have a particularly small balance and is certainlly not a "ladies watch movment [sic]". The beat rate of this movement (at 19800 BPH) is certainly not low for movements of this period. There are many chronometer-rated movements running at this frequency (and lower). There is no reason that good accuracy cannot be achieved with this movement. The power reserve of 54 hours is quite good. Criticisms of this movement usually center around the relative inefficiency of the automatic winding mechanism and some wear problems (without proper maintenance) with the center wheel pivots and rotor pivots (only on the 17 jewel version - not the 30 jewel).

    FYI: The spelling is Movement not Movment.

  7. #7

    Default Re: Bulova Ambassador Automatic 30 jewel (RE: jimH)

    I'm not dumping on the movement by any stretch; the accuracy of this movement was sufficient for them to build a chronograph on top of it. Nonetheless, the placement of the rotor effectively removes ~1/3 of the usable space, leaving an amount of space comparable to a 10''' watch or smaller. The size of the balance reflects that. 19,800 is certainly higher then most 11 or 12''' watches, but most 11 or 12''' watches have larger balances. High grade watches with smaller balances, on the other hand, would typically run at 21,800 or 28,800. The choice of 19,800 represented a compromise between accuracy and power reserve. Both accuracy and power reserve are good, in part becuase of tighter tolerances in the manufacturing.

    But at the end of the day, there's a reason why microrotor technology wasn't used more. There are cheaper ways of accomplishing the same thing.
    My growing collection of "affordable" vintages: http://www.abslomrob.com

  8. #8

    Default Re: Bulova Ambassador Automatic 30 jewel (RE: AbslomRob)

    Quote Originally Posted by AbslomRob View Post
    I'm not dumping on the movement by any stretch; the accuracy of this movement was sufficient for them to build a chronograph on top of it. Nonetheless, the placement of the rotor effectively removes ~1/3 of the usable space, leaving an amount of space comparable to a 10''' watch or smaller. The size of the balance reflects that. 19,800 is certainly higher then most 11 or 12''' watches, but most 11 or 12''' watches have larger balances. High grade watches with smaller balances, on the other hand, would typically run at 21,800 or 28,800. The choice of 19,800 represented a compromise between accuracy and power reserve. Both accuracy and power reserve are good, in part becuase of tighter tolerances in the manufacturing.

    But at the end of the day, there's a reason why microrotor technology wasn't used more. There are cheaper ways of accomplishing the same thing.
    A few things: First, the fact that a chronograph module was added to the Buren to produce the Heuer caliber 11 (with Hamilton/Buren and Breitling) really says nothing about the accuracy of this movement. Second, later iterations of this effort (the caliber 12) did run at 21600 BPH. In any case, it is not necessary for a watch to run at a high beat rate to have outstanding accuracy. Third, I'm not sure what you mean by the comment, "there's a reason why microrotor technology wasn't used more. There are cheaper ways of accomplishing the same thing." Surely you must be aware that microrotor movements are still being designed, produced and used in production watches. See, for example, the Chopard LUC 1.96, 3.96, 4.96, 6.96, etc. series of movements. These run at 28800 BPH with power reserves of 65 hours and are chronometer certified. Or consider the Universal Geneve UG 101 introduced in 2008. There are many other current examples of this rotor design.

    The point of the microrotor movement is to produce a very thin automatic movement. Of course, there are design compromises and tradeoffs. You probably didn't mean it but your reply suggests that microrotor designs have come and gone. This is not true; they are very much still with us.

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