Does anyone know what this diode/rectifier symbol is? This diode/rectifier is on a small motor control board used in a horizontal milling machine. I am repairing it for a friend of mine and wanted to make a schematic. The diode checks like a standard diode, so it is probably good.

The milling machine is probably late 1950's or early 1960's. It contains a other "antique" electronics parts like a "non polarized Klep-Sel selenium diode" (which I have identified from an old International Rectifier spec sheet) (roughly equivalent to a modern MOV) and it contains a 20A stud mount SCR (which I have also identified) and it contains an (old school) glass encapsulated bimetal protector (resettable breaker).

I have been working on electronics for 50 years and have never seen this diode/rectifier symbol used, so I would like to identify it. The diode is similar to the old "top hat" diodes used in the early 1960's. A Google image search does not turn up anything like this.

 

The bar at the end shows a typical diode symbol, nothing strange!
Ignore anything else.

 

Hi LDC1615,

Your depiction of the symbol is incorrect.

It is to be depicted as follows.



Nandu.

 

Does anyone know what this diode/rectifier symbol is? This diode/rectifier is on a small motor control board used in a horizontal milling machine. I am repairing it for a friend of mine and wanted to make a schematic. The diode checks like a standard diode, so it is probably good.

The milling machine is probably late 1950's or early 1960's. It contains a other "antique" electronics parts like a "non polarized Klep-Sel selenium diode" (which I have identified from an old International Rectifier spec sheet) (roughly equivalent to a modern MOV) and it contains a 20A stud mount SCR (which I have also identified) and it contains an (old school) glass encapsulated bimetal protector (resettable breaker).

I have been working on electronics for 50 years and have never seen this diode/rectifier symbol used, so I would like to identify it. The diode is similar to the old "top hat" diodes used in the early 1960's. A Google image search does not turn up anything like this.

Thanks Nandu for the correction to the drawing. I forgot the cathode line. Here are the corrected pictures.

 

Hi LDC1615,

Here's another old symbol for a zener diode.

It's similar to the one you have shown.



Image credit: Understanding Electrical/Electronics Schematic

Nandu.

 

Hi LDC1615,

Here's another old symbol for a zener diode.

It's similar to the one you have shown.

View attachment 316881

Image credit: Understanding Electrical/Electronics Schematic

Nandu.

Yes, I saw that zener symbol during my research, however the right angle is on the cathode with the above symbol. The symbol is clearly on the anode for the unknown diode. Honestly, I believe it to be a zener diode, so I am going to apply a voltage to a resistor in series with this diode to test the voltage drop across the diode.

 

Keep us updated of your results!
My curiosity is piqued!!

My bet is that it is a breakdown diode.

 

Unknown Diode Symbol Solved!

I connected a 10K resistor in series with that diode and connected to a variable DC power supply. I measured the voltage drop across it. It measured 12.1V, so it must be a zener diode. I pulled the diode out of the circuit and there was very faint writing on it. The brand was clearly marked GE, but the numbers were very faded and almost impossible to read. I used a UV light and could read Z4XL22B, An old GE cross reference sheet showed similar numbers, indicating it was probably a zener diode, but it was not an exact match. This GE Z4XL22B tested exactly how the GE Z4XL12B in the cross reference would have tested.

I also found a Google reference to that diode number crossing to a
22.0 Volt 1 Watt Zener Diode - NTE5080A

In an old GE SCR manual (dated 1964 and available for download from SteamPowerdRadio.com), I found a reference to that diode (GE Z4XL22B) with a similar symbol in the schematic.

Here is an interesting history of early GE semiconductors.

https://sites.google.com/site/trans...ductor-manufacturers/general-electric-history

Since the diode did not test bad, (but not zenering at 22V) I am not going to replace it, because I got the milling machine motor drive operational by replacing the defective stud mounted (GE) 20A SCR.

So I am going to call this an early zener diode symbol (before standardization?) that perhaps history forgot!

 

The "L" line represents a 'knee' voltage. Was in my sixties electronics course.