Hello all, I am currently repairing an old Rotel RA-812 and have struck a problem (well, hopefully not a problem). Having tested it etc, I discovered one channel had 37 Volts or so on one of its outputs, which is not good.
I traced the problem to the driver transistors, one of which was open circuit and the other was fused closed circuit. But then I still had DC on the output, to the tune of 13 Volts. After some more prodding I discovered one of the output transistors had no emitter connection and had a resistance of 100 Ohms between the collector and base. Something strange about the design is that it uses two of same transistor per side, rather than a complimentary NPN/PNP pair.
Now here is my problem, the output transistor is a 2SD427 and none of the suppliers here stock it, the best they can do is a couple of weeks wait at a cost of $35 which I am not too thrilled with. Can I use a 2N3055 in its place? Obviously if using a different transistor then it would be best to replace both the transistors in the channel, or even the amp which is not a problem for me as the 2N3055 is readily available and very cheap. Any info or help as to whether it will work satisfactorily would be great. A bit of a long story for a simple question, but hopefully it was interesting
I'm looking forward to hearing this amp, as inside its built like a tank and has lasted well with just a couple of niggles to sort out. Has anyone had any experience with this amp?
I traced the problem to the driver transistors, one of which was open circuit and the other was fused closed circuit. But then I still had DC on the output, to the tune of 13 Volts. After some more prodding I discovered one of the output transistors had no emitter connection and had a resistance of 100 Ohms between the collector and base. Something strange about the design is that it uses two of same transistor per side, rather than a complimentary NPN/PNP pair.
Now here is my problem, the output transistor is a 2SD427 and none of the suppliers here stock it, the best they can do is a couple of weeks wait at a cost of $35 which I am not too thrilled with. Can I use a 2N3055 in its place? Obviously if using a different transistor then it would be best to replace both the transistors in the channel, or even the amp which is not a problem for me as the 2N3055 is readily available and very cheap. Any info or help as to whether it will work satisfactorily would be great. A bit of a long story for a simple question, but hopefully it was interesting
I'm looking forward to hearing this amp, as inside its built like a tank and has lasted well with just a couple of niggles to sort out. Has anyone had any experience with this amp?
B&D Enterprises (which is a good US source for many Toshiba and other 2SA/SC etc. transistors) shows MJ15015G as a replacement. You would need to verify that that is indeed a suitable replacement.
There is also a thread here on replacements:
http://www.diyaudio.com/forums/parts/163562-2sb557-2sd427-replacement-options.html
There is also a thread here on replacements:
http://www.diyaudio.com/forums/parts/163562-2sb557-2sd427-replacement-options.html
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