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Tim Schwartz[_2_]

On 4/12/2016 2:34 PM, wrote:
I have an older QSC model 1400 in with some blown output transistors (uses 8 per channel). Original outputs are Toshiba 2SD424 and B554. QSC doesn't sell parts for this amp any longer because of it's age. Is there a reliable source of these outputs, or should I replace them all with something newer?

Hello,

Toshiba discontinued these years ago, and anything on the market today
is likely to be a 'fake'. I would tend to use a device like the these
from Motorola/ ON Semiconductor:

For the 2SD424 use an MJ15024G

2SD424 spec:180V 15A 150W 40-140 beta. 5Mhz

MJ15024 spec: 250V 16A 250W 15-60 beta. 4Mhz

The PNP compliments are 2SB554 and MJ15025G.

Order genuine On Semi ones from a source like Mouser or Digikey for
around $6. If you have the ability to, then I would try to beta match
each bank of NPN's and PNP's. It is not as important that the betas of
the NPN's match the PNP's. OnSemi is not a consistent as the old
Toshiba devices, where all of the transistors of a lot number were quite
close in beta.

CHECK THE BIAS CIRCUIT, or you might be replacing them twice.

Regards,
Tim Schwartz
Bristol Electronics