Replacing driver transistors Lab Series

[phydauex]

Looking for thoughts, suggestions:
Repairing a L5 Lab Series that has had some major issues, need to replace both driver trans in the output section (RCA410). Thes seem to be non-existent, but came across a ST device MJ15024 that has better specs with the exception of slightly lower gain range (hfe 15-60 compared to hfe 30-90). Using it as a driver, is that going to have enough gain to work? It definetely has enough current available (20A compared to 7 A).

Thoughts or other suggestions? These devices are definetely dead shorted and drawing huge current when powering up, even with a light bulb limiter, plus they test shorted on my transistor tester.
Matt

[Steve Conner]

What's the voltage? The MJ15024 is designed for 250V and that limits the gain. You could try the MJ15003, which is rated 140V and has a minimum gain of 25 at 5 amps.

Now, in transistor amp speak, the devices that drive the speaker are called the output transistors, and the smaller devices that drive those transistors are called the drivers. Your TO3s are probably the outputs, typically you don't see TO3 drivers until you get into the 400+ watt range.

I think Peavey used the same transistors for drivers and outputs, but they selected them. The ones with high gain at low currents ended up as drivers, the ones that performed better at high currents ended up as outputs.

PS: Watch out for fakes, both the MJ15024 and MJ15003 are widely counterfeited.
http://sound.westhost.com/fake/counterfeit-p1.htm

[Enzo]

NAh, drivers. The row of outputs are RCA 1B05 or something like that (or a Delco type - don;t mix), with the 410 at the end of the row driving them. All TO3.

[Steve Conner]

Oh, so it is a big badass amp.

If the drivers have blown, I'd suspect the outputs too.

LAB Series L5 amp: RCA transistor equivalent?

This thread says the rails are +/-55V and recommends the MJ15003 as a replacement. I guess it would work OK in both the driver and output positions.

[Enzo]

Here is the L4 power amp for reference. If it is not the same as the L5, it is at least darn close.

Note the transistor pinouts, upper right, are oddly enough "top view" so they all appear "backwards."

[phydauex]

Thanks everyone, looks like Newark has them in stock, plus some of the other upstream transistors, that I may order just because. The outputs seem to be ok, at least they test ok. We'll see when I get the power restored to the circuit without blowing a fuse. Initally I found that the power board that attaches to all the output sockets had broken all of the solder joints and I'm sure some things shorted/blew in the process. I don't know however if the devices went first or after the solder conections came loose.

I will be interesting to see. This is my third L5 that I've fixed, all from the same guy, I think he was stocking up on them or something. Anyway first two were succesful, I'm hoping this one will be also.

Thanks for the responses,
Matt