2n3055, mj21193, mj15004 pics (for detecting counterfeits)

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The picture says it all - from left, they are:

2n3055 (Motorola, genuine)
mj21193 (On, genuine)
mj15004 (On, genuine)

For those who suspect they were sold counterfeit mj1500x devices, this should provide a good frame of reference.

Note the difference in die size and bonding wire thickness between the two MJ devices and the 2n3055!

I measured the 2n3055 die at 4.41 mm^2, whereas the mj21193 is about 26 mm^2 - that's a difference of almost 6x!

No wonder the mj21193's are so hard to kill in comparison. I'm going to try and get some "off brand" 2n3055's just for fun to see how they stack up to the genuine motorolas as well.

On a related note, does anyone have a good method for getting open a TO-247 or TO-264 flatpack without obliterating the contents?

I have some 2sc1302 and mjl1302 series here that I wouldn't mind sacrificing as well, just to help the cause.

There are more pictures at the url below, including shots of the rear finish of the TO-3 cases, closeup shots of the ink printing on the TO-3 cases, and front and rear shots of a genuine mjl1302a device (I was surprised the rear finish looked as poor as it did, actually.)

If anyone has any requests for better photos of any part of the transistors, let me know - I didn't throw them out, obviously. All three still work just fine, which is surprising considering the hell I put the poor things through.


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Hi Brian,

Glad Austin worked out with the heatsinks & caps! I bought a couple of larger ones (heatsinks) for a (shock, horror) Death of Zen I'm building.

Dustin, Brian's referring to an actual Radioshack.com store north of Atlanta that's (unfortunately) shutting down. As of last Friday though, my last trip down there, it was pretty much cleaned out (with my assistance :). They're probably within a week of putting out the cat.


That's good, because they are. =)

The entire point was to give people an idea of what a *good* device should look like if they think theirs are fakes.

I'm still amazed by the size of the mj21193 die in comparison to the poor 'lil 3055.

It'll be interesting to see the construction of the mjl21193 once I get these flatpacks apart.
Retired diyAudio Moderator
Joined 2002
Sidney- Thanks for telling me about Austin Electronics. It is nice to have a decent local surplus store. The heatsinks are nice and heavy. Which ones did you get? the 8x9x2.6?

Damon- I am located in the middle of Atlanta, currently living in the Georgia Tech dorms. I am co-oping up in Marietta this semester.

On a side note, I was at a military conference on DMSMS (diminishing manufacturing supply and material shortages) the last few days in New Orleans, and there were quite a few companies that made high quality semiconductors, basically components that have lower tolerance and operate in a higher heatrange. I am wondering how using these parts would improve the sound quality of an amplifier. I have seen substitute higher quality parts for just about everything except for the transistors. I am wondering how this will work out. I have brochures from a few companies, and I will see if I can get some samples.

An externally hosted image should be here but it was not working when we last tested it.

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