Motorola U8344 U8338. Who knows these guys?

[galbip]

Hi guys, I'm trying to repair a old linear power supply I build at school 30 years ago....

I couldn't find any reference to the two TO-3 power devices.

One is marked U8344 the other U8338 A both components have Motorola logo.

Can someone help me?

Thank you

[tunk]

Maybe they are date codes?

[galbip]

I have attached a picure.

They both report K75MEX, perhaps is the foundry reference

[picburner]

In fact the correct name is "K75MEX", the other numbers are datecodes as tunk rightly told you.
There is no datasheet on the net, only some sites (like Aliexpress) that sell it.
Based on the characteristics of the power supply, try to find a replacement if they are broken.

[amyk]

https://www.eevblog.com/forum/chat/help-finding-specs-for-transistor-u8425/

Suspiciously similar...

[gorge441]

I guess you already got whats you want to know.
Anyway, It is a data code and the RCA databook will help you to find.

[galbip]

Thank you for your support.
Actually, no way to find datasheet.

Following the traces on PCB, the two devices are connected in parallel with 0,33Ohm balancing resistors on the emitters.
One is dead...

So any power NPN transistor should do the job.

Thank you

[SilverSolder]

https://www.eevblog.com/forum/chat/help-finding-specs-for-transistor-u8425/

Suspiciously similar...

...complete coincidence.  Gotta love synchronicity...

[galbip]

Okay.... I give up.....
It seems impossible to find information on these K-series devices....

However, I found this link with many very old databooks:
http://www.rsp-italy.it/Electronics/Databooks/

hope can be useful to someone.

[Circlotron]

So any power NPN transistor should do the job.

Make sure it is for linear use, not switching.
Linear one will have better SOAR.
https://en.wikipedia.org/wiki/Safe_operating_area

[coromonadalix]

like 2n3055, 2n3771  ...

the k75   i dont think its a darlington ??

[M0HZH]

If it's a linear PSU you built in school, almost certainly it would use 2N3055 or similar; it was the "de facto" transistor for such applications back then. Plus, it's probably a generic design that would work with any high-power NPN.

[SilverSolder]

So any power NPN transistor should do the job.

Make sure it is for linear use, not switching.
Linear one will have better SOAR.
https://en.wikipedia.org/wiki/Safe_operating_area

Is this true of bipolar as well as MOSFET?

[coromonadalix]

you can make psus with mosfets too   yes