I am repairing a power supply and I need to replace a couple of transistors that test bad (shorted between all terminals).
Unfortunately the transistors are no longer available and I can not find any datasheets. I am relatively new at this so I don't know where to look.

TO-3 package, PNP
part number:
STi
108-020k
0046


Edit: another note would be that the diodes and resistors are on the board, so I know that there are none internally. EBJ 0.512, CBJ 0.432 for the remaining NPNs

 

You could use a substitute with a current rating of 2-3X the max supply current.

 

I didn't think it would come up, but this power supply is kind of different, it is for a scientific instrument that is basically an ultrasonic element. It's output is a 20khz sine wave. I know that the supply input current is 4A, but that is it. Specifications are unavailable for the output, although I know that it is high voltage and has a maximum output of 400w. Schematics are unavailable and the PCB is a little bit complex. I don't know the principles of operation.

Here is a link to the users manual, if it matters:
https://medschool.vanderbilt.edu/cdb-core-lab/files/cdb-core-lab/public_files/250-450 User Manual.pdf

If I sketch out my circuit I suppose I may be able to determine the current by looking at the current rating of other components such as diodes.

 

Possibly an NTE cross match.

 

Here is the logo on the thing. Anyone recognize it? Almost looks like STmicroelectronics.


Would opening the transistor package tell me anything?

 

Update: I found the transistor manufacturer. "Semiconductors Technology Inc." of Florida.
http://semi-tech-inc.com/browse1semi.asp
I identified the logo using this excellent website:
http://how-to.wikia.com/wiki/Howto_...rcuit_(chip)_manufacturers_by_their_logos/P-T

I have contacted STI for assistance in identifying the custom part no. Hopefully they can get me the exact transistor model. Currently, I think it might be a BU108

 

Here is the logo on the thing. Anyone recognize it? Almost looks like STmicroelectronics.
View attachment 87615

Would opening the transistor package tell me anything?

As long as the chip isn't too melted - NS used to publish transistor data books with pictures of the die layout in the back pages, these all had a reference number and a list of typical devices that used that fabrication pattern.

Can't remember whether there's any NS databooks on archive.org - but it can't cost you anything to look.

 

Possibly an NTE cross match.

You are right, I came across this. I think this is what I will go with. Thank you.

 

You are right, I came across this. I think this is what I will go with. Thank you.

There's still a bit of guesswork - you can probably narrow it down to 2 or 3 dozen type numbers, then look up the specifications and select one that looks like it can handle it.