Pioneer SA-900 Recap Part 2

Finally wanted to post some images of my SA-900 after the restoration.   Final bench test on a 4 ohm load resulted in a 50w/ch before any clipping occurred.  Back ground noise was low.  The only thing I didn’t like was the volume control didn’t track evenly at the lower levels.  The problem exhibited was that one of the channels was a tad higher when the volume was down low.  It was considerably noticeable, but balanced back out when the volume hit 12 o’clock position.  To reduce this tracking error, I installed a couple of resistors on the volume control on the left channel to bring the volume down.   I also had to install a resistor on the right channel at another point to bring to hold the right channel down after the volume went from the 12 to 5 o’clock position.

Overall the final results I think turned out very well.  A couple days later I attended a local group and brought this amp along with my A-717 to compare with a Dynaco 70, Sansui AU-717, and a Pioneer SA-9500.  During our A-B comparisons we really had a hard time noticing and discernible differences between the SA-900, and the others.  Granted we were listening at moderate volume levels on some Altec Lansing 604’s.  By the way 604’s are really efficient speakers so its rather easy to drive these to high SPL with low power.   So in no way will I say that this is the same as a tube amp or the high power solid state amps.  What I will say is that its quite a testament to the engineering that went into each of these amps that allows them to sound so good considering the 20+ year span that these units were originally made.

Anyway, here are few photos of

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3 thoughts on “Pioneer SA-900 Recap Part 2”

  1. Hello there. I was listening to my sa900 recently when it shorted. I traced it to a rectifier diode in the power supply. I have new ones in hand but was thinking I might replace the transistors on the board as well. What are good replacements for the 2sc486 and 2sc485 transistors? I am having trouble finding an equivalent

    1. Craig,
      I’d double check that the transistors are ok before replacing them. They might be fine, but if you do find one that is acting up then I’d probably replace both transistor on both channels just in case the gain is different. As for an equivalent, I did search nteinc.com and found equivalents. the 2SC486 is a NTE324 and the 2SC485 also crosses over to a NTE324. If you hunt hard enough you might still find those transistors from Toshiba from various vendors, but it does look like its pretty much obsolete. Otherwise if the NTE equivalent doesn’t work you’d have to source one from a donor unit.
      -mike

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