Philips 22AH578 - strange semiconductors

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I am currently working on a philips 22ah578 amplifier. The schematic of this monster can be found here:

One channel is not working, I already figured out that some of the TO-3 type power transistors are dead.
I am very confused about the semiconductors which are used in this amp, never saw those before and I guess those were OEM made for this project.
The power and driver devices are Toshiba items, the power devices are labeled "355N1" and the driver devices are labeled "357N1" and "357P1". The small signal devices are mostly motorola, also having strange numbers.
Anyone else been working on such an amp before? Which common types can be used as replacements? I`ve read some information about the amp in this thread , so I`m not quite sure if simply taking MJ15003`s is the best way...

thanks, audiomatic
They are probably just "factory numbers" for common transistors. IMO this practice should be banned!

I'd agree, MJ15024 should be suitable as replacement outputs. As for the drivers (looks more like pre-drivers in that topology) what kind of packaging are they in? If they are TO-220 then MJE15032/3 will probably work. If they're TO-126 or similar i'd try MJE340/350
The drivers are TO220 and Japanese (green/black), A968/C2238 or earlier types.

Which likely makes the output devices 14MHz Toshiba 2SB600/2SD555.
As they'll cost in the order of $10/pc to replace, MJ15024/MJ15025 or the upgraded MJ21195/MJ21196 types would be the economical substitutes.
spind said:
Quasi-complementary amp here.

Oops, yes.
I was looking at this picture, the green/black complementary devices should be the pre-drivers.
Makes it only 2SD555 for the outputs.


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this circuit looks like an old RCA circuit uprated for 200W. They used RCA-1B05 outputs and another for the driver and1E02/3 for the NPN/PNP pre-driver pair. They used to package pnp's in green and npn's in black TO-220, but the 1E02/3 I think were TO-66.
The SOA for the 1B05 was 150W to 140V, 1.07A. The MJ21193/4 match this but have 250W dissipation and much better gain linearity, so would give a performance improvement. You could probably use MJE15032/3 drivers and pre-drivers, because the gain would be higher (MJ21193/4 =25 at 8A, 1B05=15 min, 2A) but these are in TO-220.
Hi M8's
I am new on this site but I repair for a lot of years Philips audio.
I am also a owner of a complete lab series. Past week my 578 amp. was blowing up. My pre-drivers are destroy and even some head drivers. So I have to ficker out what are the closed types that works. I have found out that for head drivers MJ15024 are good. The pre drivers I have used 2SA1452 and 2SC1625 both are 1 watt with high voltage. For Q205 I have use BC639. For Q207 BC640 and Q206 BC439 both are 0,5 watt by 80 volt. After replacement the 578 amplifier is as new. Good luck everybody.
Wim ;)
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