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Can someone help me identify this rectifier?

Discussion in 'General Electronics Discussion' started by gdb, Oct 17, 2009.

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  1. gdb

    gdb

    11
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    Oct 17, 2009
    Hi,

    First, please be gentle with me, as I am a computer geek, not an electronics one ;-)

    I have just obtained and am trying to restore a 1931 IBM master clock, and am trying to determine what to replace what I believe is a rectifier:

    Since I am new, I cannot post the link to the photo, so if anyone can identify 1931 components, please send me a private message can I will send the link to the photo :)

    Preferably with something reasonably authentic, as I want to keep the clock as close to original as possible. If not, I guess I can hide a new rectifier behind something else, leaving the original one there.

    And yes, the transformer needs to be replaced (it is hanging by one screw and not original, and the twinax cable is obviously someone's quick and dirty patch job.)

    I believe the original transformer burned up at some point due to the scorch marks, and currently I think that the rectifier has failed since I am finding AC voltage inside the clock (24V) rather than 24V DC...

    Once I get beyond that, then the clock will just need cleaning and refinishing.

    Can anyone give me some advice, or point me somewhere?

    Thanks

    G
     
  2. gdb

    gdb

    11
    0
    Oct 17, 2009
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Good to see old items being properly cared for.
    The rectifier is probably of the old selenium type. It consists of stacks of selenium-on-iron disks, and each disk can handle 20-40V. The current capability is defined by their area.
    There are much more disks however than would seem neccessary for a 24V rectifier, so I won't rule out the possibility that it's some kind of copper rectifier, but the electrical function and mechanical design would be the same anyway.
    These can both be replaced by 4 small 1N4000 series diodes hiding behind the original.
    I was unable to see any capacitors in the clock so if there was only ac and no dc then you are probably right in that the rectifier has gone bad. Try to dismount and desolder it to have a closer inspection of it.
    Be aware that rectification without capacitors will produce an ac component as well as a dc component (as measured by most instruments).
     
  4. gdb

    gdb

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    Oct 17, 2009
    Thank you for the information! I will be removing the transformer to get access to the rectifier soon. I will let you know what I find.
     
  5. gdb

    gdb

    11
    0
    Oct 17, 2009
    Last edited: Oct 18, 2009
  6. cj_elec_tech

    cj_elec_tech

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    Oct 7, 2009
    What a wonderful contraption! :)

    To me, these 4 items look like vitreous-enameled power resistors.
    You could put an ohm meter across each one and see if it reads 7000 ohms (or there abouts - I wouldn't expect them to be particularly accurate though). However to be certain other parts of the mechanism are not altering the resistance measurement, you would need to remove one (carefully, they might be quite fragile after all this time) to measure it.
    If they are not resistors, I'd suspect them to be inductors (coils) though - they certainly don't look like fuses to me.
    I've seen old power resistors of this sort of construction and mounting like this before though, so I feel reasonably certain they're resistors.

    I agree with what Resqueline says about the other items, that's how they look to me too.
    I'd add that this unit probably pulls a reasonable amount of current when operating the contactors and other coils, so if you replace the rectifier with modern a equivelent you'll need diodes that can handle large-ish (by modern standards) currents; maybe something in the 1N5400 series?

    Have you had any luck with documentation for the clock - a circuit diagram would be a great aide, as you could probably imagine!
    Good luck! :)
     
    Last edited: Oct 18, 2009
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    I concur with cj, it does look like resistors. Too small to be a useful inductor of the era, and an inductor wouldn't be enameled.
    I wouldn't expect the transformer and rectifier to be rated at more than 2 amps, but if you find the room for the bigger 1N5400 series it'll be safe up to 6 amps.
    That old rectifier looks like it has been running hot, with the varnish melting and running behind it. Maybe the rectifier shorted first and that killed the transformer, or maybe a damaged coil somewhere else in the clock overloaded the rectifier first. You'll find out in due time though, just put a suitably rated fuse in there somewhere if there is none.
     
  8. gdb

    gdb

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    Oct 17, 2009
    Thank you both for the answers!

    The closest I have come to finding any documentation os from a different model made a few years later, that does not have all of the "add on's" that this one does, but it is a start:

    http://williamkapp.tripod.com/id43.htm

    The mounting holes for the original transformer form a rectangle 6" x 2.5" although it is possible it was mounted on a piece of wood with terminals that bolted to those mount points.

    I will try to get some readings on the 4 devices and see what I can get.

    It is a wonderful contraption, and for the minute or two that I had it plugged in after a careful inspection, all appears to work, it is loud every minute when it activates a solenoid to wind the spring, activates a solenoid to incrementally turn that big stack of brass dials in the middle (that controlled "school" bells), and activates a relay to send a pulse out to advance any connected secondary clocks, but it was doing all the right things!

    I suspect it will be a "little" quieter when I get the transformer/rectifier situation ironed out so that the relays do not buzz. But the solenoids make a nice "clunk" sound when they activate. I have some of the secondary clocks running in various rooms around the house with individual drivers, and they each have the same solenoids in them, I can deal with that sound.

    Thanks again for your help!


    It definitely will not hang in a bedroom ;-)

    [edit to fix the URL]
     
    Last edited: Oct 18, 2009
  9. gdb

    gdb

    11
    0
    Oct 17, 2009
    I also wrote a letter to the IBM archives last week in the hope that they may be able to find some documentation for this model with the options it had. Maybe I will get lucky there.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It seems the rectifier is being activated by the master relay and only supplies the winding solenoid (& maybe prog. sol.). A 1 (or 3) amp fuse seems to be used. A bad rectifier would make the winding action louder than normal. Try to measure ac & dc voltages on it when it's winding. The rest of the clock seems to run on ac only.
     
  11. gdb

    gdb

    11
    0
    Oct 17, 2009
    If I understand the system and the schematic, the A and C connections (Since the clock advance pulse would coincide with the program advance and the winding coil, and now, after looking at one of the clock wiring diagrams, it has A, B, and C) should pulse 24VDC once per minute, which is what the secondary clocks are rated for. (The secondary clocks are somewhat simple solenoid steppers, that advance once per minute) B should be the "sync" signal indicating that a remote clock is at it's sync point for system resets after a power failure. I will verify what I see on those terminals.

    Hope this helps a little.
    Sorry for the obtuse wording there :)

    These schematics should be close to what I have, as the IBM secondary clocks were 24V for decades, even if they diagrams are 7 years after my clock was made.
     
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