MJ15015 is the modern On Semi replacement for 2N3055. Has a defined SOA in addition to the 2N3055 specs. A little faster ft, might need 20 pf cap across be leads to prevent oscillation in some circuits. The MJ15015s I purchased in 2010, were made in Mexico. Newark.com is not known for selling fakes. I've had good luck with NTE parts, but they are pretty expensive. I replaced reputed 2N3055 (actually RCA 574844) with NTE181 matched pairs, also NTE60. I paid $9 for the NTE's in 1985, paid $1.67 for the MJ15015's in 2010 (plus $7 freight from NC).
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That'a what I thought too, but then I found this:
http://www.diyaudio.com/forums/swap-meet/125248-fs-15-pcs-genuine-toshiba-2n3055.html
http://www.diyaudio.com/forums/swap-meet/125248-fs-15-pcs-genuine-toshiba-2n3055.html
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modern Q can have all of higher ft; higher, flatter hfe, better thermal ruggedness from modern packaging - what exactly is there to like about 2N3055 vs any of the last decade or so audio power output specific Q?
I have heard someone restoring a early Neve studio mixing board complaining they couldn't find "period" steel can 2N3055
I have heard someone restoring a early Neve studio mixing board complaining they couldn't find "period" steel can 2N3055
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They are perfect when you enjoy the challenge of making a great amp from
obsolete materials, pitting your own design skills against respected classics.
There is nothing wrong with 2N3055 that a clever design can't work around.
Some of the new parts are so easy to drive, its almost cheating...
I agree, Although not the HIGHEST QUALITY,But you can still build a decent amp out of a handful old cheap parts. 
Remember they are what the industry standard was back in the day ,and, was the higher
power step above tube amps of the day!
They still sound good up to the 80 watt level at least IMHO!
They were what color tv did to black and white tv, and, many have never seen or heard of black and white tv's or phones that you had to dial for that matter. He,he,he
Keep on DIYin' !!!!
jer
Remember they are what the industry standard was back in the day ,and, was the higher
power step above tube amps of the day!
They still sound good up to the 80 watt level at least IMHO!
They were what color tv did to black and white tv, and, many have never seen or heard of black and white tv's or phones that you had to dial for that matter. He,he,he
Keep on DIYin' !!!!
jer
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What amp are you going to built? Is it a good amp from the past? There must be still available original 2n3055 from local junk shop.
The best 3055 I found are R C A. there is a big stock of cdil also .can get them for you down to earth price contact vedmitraa@gmail.com
"ancient" parts ??
There are so many MJ15024's out there (below) , I have dozens of em'... You could build a nice quasi amp with 2 pairs of them , some mje340/350 for the VAS /small sanken outputs for the drivers. 3055's are just too old , can't use high rail voltage , .8mhz Ft
PA system E-waste is mostly the MJ's (20-25years) now , I have a box of them.
I will design one (mj15024 amp) in august.
OS
There are so many MJ15024's out there (below) , I have dozens of em'... You could build a nice quasi amp with 2 pairs of them , some mje340/350 for the VAS /small sanken outputs for the drivers. 3055's are just too old , can't use high rail voltage , .8mhz Ft
PA system E-waste is mostly the MJ's (20-25years) now , I have a box of them.
I will design one (mj15024 amp) in august.
OS
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I think you can build a good amp using 2N3055/MJ2955. ST and ON Semi sell good devices. The ON Semi devices have good SOA in their latest data sheets.
Some later RCA transistors were fast epi types too. If you trawl through the various threads here, I have recommended BD139/BD140 drivers with a BD139 bias stabiliser all on the same heatsink and obtained very good quiescent current thermal stability. The BD139/140 devices have better fT than MJE340/350 and higher gain at higher current. I've reported a spot measurement of fhfe for an ON Semi and ST devices which were over 50 kHz, so they perform a lot better than the old hometaxial RCA transistors. I built quite a few power amps in the 70's with RCA H_2N3055, but I have to say compared side by side with the epi devices, those amps were definitely short on high frequency response, so this is probably where the "don't use 2N3055's" originated, which I think also is echoed in Self's book. Since ST probably use the same line for TIP3055/TIP2955 there should be no difference using good old TO-3 cans.
Some later RCA transistors were fast epi types too. If you trawl through the various threads here, I have recommended BD139/BD140 drivers with a BD139 bias stabiliser all on the same heatsink and obtained very good quiescent current thermal stability. The BD139/140 devices have better fT than MJE340/350 and higher gain at higher current. I've reported a spot measurement of fhfe for an ON Semi and ST devices which were over 50 kHz, so they perform a lot better than the old hometaxial RCA transistors. I built quite a few power amps in the 70's with RCA H_2N3055, but I have to say compared side by side with the epi devices, those amps were definitely short on high frequency response, so this is probably where the "don't use 2N3055's" originated, which I think also is echoed in Self's book. Since ST probably use the same line for TIP3055/TIP2955 there should be no difference using good old TO-3 cans.
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