Stabistor?

[cncjerry]

New to me is something called a stabistor.  It is an epitaxial diode that provides a stable reference voltage.  Sometimes called a stable resistor.  It shorted out in a tape deck I am repairing causing the front panel LEDs to not light correctly. I put a glass switching diode in its place and things are much better but not perfect.  I can still see a faint, flickering glow in some of the lights that should be off completely.  OK, I am being picky.

The device I replaced is an MA29a, aka MA2C0290A. The "A" version has a forward drop of .56 to.61V across its current range.  A glass diode is OK, but not quite perfect.  I looked for a sub without luck, nothing on eBay, etc.  It is used to drop 5.0V down to approx. 4.4V.

Know of a sub?

Thanks

Jerry

[moffy]

Can you specify the current through it, or range?

[amyk]

How much current? Perhaps a suitably configured LDO may work.

[Victorman222]

Good day

A stabistor is just a silicone diode (or series connection of many) with more tightly guaranteed specs.

Usually made in multiples of a diode drop, 0.7, 1.4 and 2.1, in old times they were used as references because zeners at low voltages are bad. Also were used for temperature compensation, as each diode junction has about -2mV tempco. Also vaguely remember that selenium stabistors also exist...

Reading datasheet for your part, the 0.56-0.61V is the initial voltage tolerance, and only at If=1.5mA. At 50mA it drops 1.1V

I would suggest just picking a silicone diode with about the right voltage drop. Stabistors aren't really a thing these days

For fun attached is a picture of the inside of a 1.4V stabistor, inside its just two silicone diode dies soldered together.

[cncjerry]

I suspect the glass diode I put in there, not unlike a 4148, isn't dropping enough voltage. When the factory installed stabistor failed, it shorted.  While shorted, it turned on four LEDs in a 4x7 front panel matrix for some reason.  Now the same four LEDs are barely on, during the day you wouldn't see them.  I need to measure the drop on the diode I put in there as it draws operating current.  According to the ECG bag this diode was in, its Vf is 1V at 200ma. I had grabbed the first diode I found. That ECG diode must be 40yrs old.

Thanks for the input.

Jerry

[xvr]

I recently came across an interesting note in the description of the ZMM series of zener diodes.
Note #3 to the zener diodes parameter table:

The ZMM1 is a forward-biased silicon diode. Therefore, all parameter indices should be "F" instead of "Z." Connect
the cathode to the negative pole.

So, essentially, it's a stabistor (disguised as a zener diode among its peers).

[cncjerry]

The glass diode I put in instead of the stabistor, has a forward drop of .46 to .52 under normal load, which is a little lower than needed.   It was driving the anodes of three LEDs, but the voltage I am reading is RMS, not the instantaneous peak, because the lights are all pulsed in a matrix. It was an ECG 109, a point contact germanium diode, probably not the best choice.  I wish I had my curve tracer running to plot it against the chart of the stabistor.  First time the curve tracer would have helped!

I started to pull the front panel apart and changed my mind.  I can't see the other lights in the daylight and at night there is only a very light glow.  Though it annoys me and I like to make the decks perfect when I restore them, this front panel has been off too many times and I start to worry about cracking the PCB.  It has 15 or more screws holding the PCB to the front plastic.

Thanks again for all the input.

Jerry