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Thread: Stabistor diode

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    Stabistor diode

    Hi all!
    I have a 1994 Harman Kardon Citation 17s on the bench and the left side preamp board needs what looks like a GE 644 stabistor which seems like two diodes in series.
    I have searched for hours to come up with a data sheet on this thing and I can't, so can someone direct me somewhere else for info , or will just two fast switching diodes in series do the trick?

    Thanks in advance!

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by Steve25 View Post
    Hi all!
    I have a 1994 Harman Kardon Citation 17s on the bench and the left side preamp board needs what looks like a GE 644 stabistor which seems like two diodes in series.
    I have searched for hours to come up with a data sheet on this thing and I can't, so can someone direct me somewhere else for info , or will just two fast switching diodes in series do the trick?

    Thanks in advance!
    As your left side preamp board needs this part, is there one on the right side? If so, what does it measure like? You may have to lift one end of the part from the circuit so you can measure it with your DMM. Is it two diodes in series, both same direction, or opposing (cathodes joined or anodes joined)? Diode in series with a resistor, or even a thermistor? Is it in contact with a heat sink or part that changes temperature in operation, to provide thermal tracking? If it's a zener diode, then you'd need to determine what the breakdown voltage is (can be done with a power supply and series resistor to limit the current, and measure across the diode). A photo would help us too.

    One of us also might have an old GE Semiconductor data book....I have one from the late 60's, though it's tucked away in my storage locker someplace.

    https://www.eevblog.com/forum/chat/s...t-a-datasheet/

    https://www.antiqueradios.com/forums...p?f=8&t=319150

    ge_transistor_manual_1964-ch17_snap & stabistor diodes.pdf This is the pertinent section in a 1964 GE Semiconductor Data Book that covers stabistors

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    Last edited by nevetslab; 03-16-2019 at 05:02 AM.
    Logic is an organized way of going wrong with confidence

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    Hi and thanks for the reply!

    The schematic shows this as 2 diodes in series, and nether are Zener's.
    It does test out different resistance wise then the same diode in the channel that works

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by Steve25 View Post
    Hi and thanks for the reply!

    The schematic shows this as 2 diodes in series, and nether are Zener's.
    It does test out different resistance wise then the same diode in the channel that works
    In the circuit, what is the voltage drop of the 'working' stabistor? You at least have that as a benchmark, as it seems you'll have to cobble some suitable diodes to function at that GE part. If the result is close, and remains stable over temperature (might need a hair dryer or heat gun to asses this), your replacement part might need to be duplicated so both channels now have the same characteristic.

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    what looks like a GE 644 stabistor which seems like two diodes in series.
    What makes you think so? Do you have a schematic? If yes, please post it.

    A stabistor is a diode with a precisely defined forward voltage - unlike a zener which has a defined reverse voltage. Several single diode chips may be wired in series for higher forward voltage. A stabistor should preferably not be replaced with normal diodes.

    To find a replacement you should measure stabistor forward voltage AND current in the working channel.

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    Old Timer olddawg's Avatar
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    If it’s a “stacked” diode it should have a forward voltage drop around that of 2 diodes in series unless it is something exotic. Around 1.4vdc. We used to see them a lot in old Pioneers, Sansuis, Yamahas and such. When they became unavailable I just used small rectifier diodes in series to equal the number of diodes in the original and was careful to set the bias. Make sure it’s bad. I rarely saw a catastrophic failure in one. They were fragile and usually a clumbsy customer or an “unexperienced” tech would break the lead off of one since they were frequently mounted to the heat sink.

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    I checked both stabistor's out of circuit and the one from the bad channel test out for a lower resistance then the good one just like one diode of the pair is shorted if I recall right.
    I will double check this tonight and report back in the morning.

    Thanks all!

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Steve25 View Post
    I checked both stabistor's out of circuit and the one from the bad channel test out for a lower resistance then the good one just like one diode of the pair is shorted if I recall right.
    I will double check this tonight and report back in the morning.

    Thanks all!
    Numbers please?

    What does it actually do in that circuit?

    What isn the reported problem?

    Why do you think it´s the diode´s fault?

    Is it the factory original diode?
    Somebody might have replace the dual pack with a single one, not knowing better.

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    Juan Manuel Fahey

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    Supporting Member Jazz P Bass's Avatar
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    Here is the schematic: harman-kardon-citation-17s-preamplifier-service-manual.pdf

    It would assist all if the OP would identify which 'stabistor' is in question.
    There are a few on the diagram.
    Some are used as voltage references.
    One is in the output bias chain.

    There are well defined voltages marked on the schematic.
    I would use those as a troubleshooting tool rather than 'resistance' of a diode.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Steve25 View Post
    I checked both stabistor's out of circuit and the one from the bad channel test out for a lower resistance then the good one just like one diode of the pair is shorted if I recall right.
    I will double check this tonight and report back in the morning.

    Thanks all!
    What you need to measure is the forward voltage drop across it at a known small current. Some meters have a diode test range but they seldom go more than a volt. Get a 9V battery a 4.7K resistor. Put all in series with the diode and report the drop across the diode.

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    Old Timer J M Fahey's Avatar
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    And again: what is the problem we are trying to solve?

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    Juan Manuel Fahey

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