hFE for 2N3055 transistors

[62vauxhall]

I have examples of two TO3 2N3055 transistors from two different manufacturers. Motorola which were in the unit (NAD 7225pe) and new, unused ST Micro TO3 transistors that I have on hand.

The existing Motorola 2N3055 appear OK using diode mode of a DMM. But when connected to a device that happens to display hFE, the number shown is 475.

That same device displays an hFE number of 174 when connected to the ST Micro transistors

Does this mean that the Motorola 2N3055 transistors within the NAD are out of spec?

My expectation was that if the Motorola transistors were good, hFE values would be close (or closer) to those of the new, unused ST Micro transistors.

 

[rcs16]

Did you check your readings against the data sheets for those devices? Noting the same test conditions, if possible. Power transistor hfe is usually not 475, this stands out

 

[62vauxhall]

Test conditions aside, I did refer to data sheets. hFE for a Motorola 2N3055 is 70 and likewise for ST Micro.

Even though I checked the Motorola twice within the past 48 hours, I just now checked and rechecked it again. This time, the device I used to test it dislayed "2 diodes" instead of "NPN transistor".

So now I think it is safe to say that the Motorola 2N3055 is bad.

 

[rcs16]

Could be a fake and it’s a Darlington instead

 

[62vauxhall]

It could be a fake I suppose. Each channel has a PNP/NPN pair and the output transistors on one side a differ in appearance from those in the other. I don't know if the one I found to be faulty is an original or a replacement.

Since I have a couple of new ST Micro 2N3055's I may install new ones in both channels.

 

[fred soop]

The 2N3055 table shows max dc gain of 70 but the graphs show as high as 200 with very low collector current and temperature of 150C. But 475 is quite high even for a small signal device.