My NAD C 355BEE broke. I believe I connected a speaker cable carelessly and it short-circuited one of the terminals to the case next to the terminal. Seems like there was no protection circuitry for an accident like this. My Leach Amps have survived a similar incident with only a blown fuse. This also blew both 41 V AC fuses immediately, but still not fast enough it seems.
One 2SA2121 is a short from every pin to every other pin. Also the corresponding 2SC5171 that used to drive it is shorted.
I removed all four power transistors from the heat sink and plan to replace all four power and all four drive stage transistors.
There are no 2SA2121 or 2SC5949 available anymore. Lenbrook recommended that I contact my local representative. They in turn recommended that I use 2SA1943 and 2SC5200. I'd myself prefer 2SA1987 and 2SC5359 because these are 180 W, instead of the 150 W of the recommended pair. The originals were 220 W (Toshiba's information here, page 7).
My first question is, should I get these from Kessler, or a local parts shop that is slightly more expensive (Partco), or from some other place in Europe? From Kessler I would buy more parts "just in case", but from Partco I'd buy only what I need and then go back for more.
My second question is, should I just use standard silicon pads that are 0.4 K/W or would there be a problem with mica and thermal paste on both sides? I have mica + thermal paste in my Leach Amps, but in the case of the NAD I wonder if the mica insulators will stay in place. There are no screws through them. Only a clamp pressing on the transistors. Is this thing even running anywhere close to its limits?
Kessler did not respond to my question about the specs of their TO3P silicon insulator, but their feedback form also gave me some fatal error after eating my message.
My third question is, should I expect to find even more damaged parts than one driver and one power transistor? I plan to power the amp up using a bench power supply with a current limiter and compare the channels using a multimeter and possibly a scope, feeding a test signal through the main in connectors. I might even simulate the whole power amplifier in MicroCap if that doesn't prove to be too difficult.
One 2SA2121 is a short from every pin to every other pin. Also the corresponding 2SC5171 that used to drive it is shorted.
I removed all four power transistors from the heat sink and plan to replace all four power and all four drive stage transistors.
There are no 2SA2121 or 2SC5949 available anymore. Lenbrook recommended that I contact my local representative. They in turn recommended that I use 2SA1943 and 2SC5200. I'd myself prefer 2SA1987 and 2SC5359 because these are 180 W, instead of the 150 W of the recommended pair. The originals were 220 W (Toshiba's information here, page 7).
My first question is, should I get these from Kessler, or a local parts shop that is slightly more expensive (Partco), or from some other place in Europe? From Kessler I would buy more parts "just in case", but from Partco I'd buy only what I need and then go back for more.
My second question is, should I just use standard silicon pads that are 0.4 K/W or would there be a problem with mica and thermal paste on both sides? I have mica + thermal paste in my Leach Amps, but in the case of the NAD I wonder if the mica insulators will stay in place. There are no screws through them. Only a clamp pressing on the transistors. Is this thing even running anywhere close to its limits?
Kessler did not respond to my question about the specs of their TO3P silicon insulator, but their feedback form also gave me some fatal error after eating my message.
My third question is, should I expect to find even more damaged parts than one driver and one power transistor? I plan to power the amp up using a bench power supply with a current limiter and compare the channels using a multimeter and possibly a scope, feeding a test signal through the main in connectors. I might even simulate the whole power amplifier in MicroCap if that doesn't prove to be too difficult.
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