Power transistors from an old Biamp mixer

[guitrslingr]

I'm working on an old Biamp 1229 and a couple of the power transistors have failed. This mixer uses NEC 2SD555 and 2SB600 transistors, which appear to be discontinued. B&D recommends MJ15024G and MJ15025G (respectively) as current production replacements. Does anybody know if these are direct replacements or do I need to replace all of the power transistors? If they're not a direct replacement, can I get away with just replacing the pairs?

[Enzo]

They are equivalent, but not identical.

In fact some old QSC amps went from the one to the other with no other changes.

But the problem is that the transistors do not work alone. There are rows of them inthe power stage, and they must share current well, and they must track thermally. If they don;t, then one of the transistors can "hog" the current, and burn up. Likewise, as teh whole amp warms up, you want all the power semis to react to the temperature changes similarly

SO you really don;t want to mix types. If there is a row of four D555s, you don;t want a lonesome 15024 in the row. All of one or all of the other.

Now if this is stereo, you might be able to swap between channels to get one side all of a type. It does not matter if the left channel and right channel use the same parts as each other.

I usually find the best prices on those MJ150xx series transistors from Allied.

[guitrslingr]

Each power amp has three of the 555's and three of the 600's. Should I replace these by the complementary pair or by type?

j.

They are equivalent, but not identical.

In fact some old QSC amps went from the one to the other with no other changes.

But the problem is that the transistors do not work alone. There are rows of them inthe power stage, and they must share current well, and they must track thermally. If they don;t, then one of the transistors can "hog" the current, and burn up. Likewise, as teh whole amp warms up, you want all the power semis to react to the temperature changes similarly

SO you really don;t want to mix types. If there is a row of four D555s, you don;t want a lonesome 15024 in the row. All of one or all of the other.

Now if this is stereo, you might be able to swap between channels to get one side all of a type. It does not matter if the left channel and right channel use the same parts as each other.

I usually find the best prices on those MJ150xx series transistors from Allied.

[zero cool]

If you have one bad 555/600 in a channel. then replace ALL the devices with the MJ's.

Save the remaining good devices to repair the 2nd channel or sell them on ebay used.

[Enzo]

Complimentary pair? No. You want each row of three to be the same type, whichever type it might be, which is what zero said.

There are no pairs. The three on one side work together, not one across from another.