"Phil Allison" wrote in message
...

"Dave M"
Arfa Daily wrote:

Anybody know what the output transistors are in a Peavey PV-1.3K high
power slave amp ? House codes 70484200 and 70474200
--


70484200 = MJ-15024
70474200 = MJ-15025


** Probably true enough - but PV use the codes for reason.

Motorola ( or "ON" ) select devices from regular stock to meet particular
customer's requirements and supply them with a code number that is
confidential.

With output transistors that are to be used in parallel sets, devices are
selected that have near identical Base Emitter voltages for given
collector currents. This is a parameter that varies quite independently
from simple Beta.

I recall seeing a test rig and procedure described by PV that allows
service techs to select output devices in this way.

Since they were released in 1977, MJ15024/5 devices have undergone several
major revisions of the chip design and along with batch and sample to
sample variations this renders older and newer examples incompatible for
parallel operation.

Also and not least, these same devices are on the very top of the list for
counterfeiters so you MUST know that the ones you buy are from authorised
sources.

Farnell and RS Components are safe sources - almost no-one else is.


... Phil


Thanks for that. It would be Farnell that I would be getting them from. I
don't think that I've currently got any in stock, but if I have, it will be
Farnell that they came from. I suppose that there are several alternatives
here. I could just go for it, and look at the voltages across the emitter
resistors to see how close a match that I've got to the others. Or I could
replace the whole set, which would be an expensive option, or I could leave
the bad pair out altogether, and maybe take a pair out of the other channel
to balance it up, if the owner doesn't use it at anywhere near the kilowatt
per channel that it claims to be.