[chbot] Transistor for Audio Amplifier Repair

[Martin Towers]

As long as the voltage and current ratings are covered almost any
transistor will do electrically.
Note that the 2SD1762 has an insulated tab so find one with the same if
possible, or you'll need an insulating kit.

Martin


On Sun, 2023-02-19 at 15:02 +1300, Spencer Travers wrote:
> I am repairing someone's much loved audio amp/receiver from the 1990s
> and need to find a replacement transistor. It is a 2SD1762DEF TO-220
> NPN bipolar power transistor. Some datasheets say it's 50V, 3A rated.
> There are some ebay listings for this part.
> 
> Does anyone have something local and suitable or some pointers? I do
> have a service manual with schematics. If anyone's interested, here
> is a 
> link: https://drive.google.com/file/d/1DhsyuLpafuNbXBOhnIgTRilbyw64tCRr
> 
> Q701 is the dead transistor, located at grid 32B in the schematics.
> 
> This transistor is used to create +15 V from the +40 V rail. It looks
> like the audio input selector IC401 shorted +15 V to -15 V and took
> out the transistor along with a couple of traces on the PCB. R405 &
> R406 and surrounding traces were destroyed. The good news is that
> injecting +15 volts from a lab PSU to where Q701's emitter was
> connected seems to make the amp work OK.
> 
> I had thought of using a 7815 voltage regulator but I think the input
> voltage would be too high. I do see some devices on ebay and may have
> to resort to that.
> 
> I guess another option would be to add a separate transformer,
> rectifier, and voltage regulator to get 15 V, but I would rather
> avoid that. Unfortunately there are no suitable lower voltage taps on
> the transformer.
> 
> Spencer
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