Uploaded February 2024 | Updated September 2026, 2 weeks ago

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Hello everyone I’m starting the weekend a little bit early. 

I have a lot of stereo receivers in my collection in various states. I am on a bias kick these days.

I’m really discovering that adjusting the amp bias and getting things within spec is reducing distortion and loudness. In addition, it’s safer for those tired old amp chips and circuits. The amplifier runs cool as designed. 

Here are the two brothers on the bench tonight:
Technics SA-550, 1984, 70WPC w/ TV tuner
Technics SA-850, 1984, 100WPC w/Space Dimension

Both of these receivers are troublesome and took a few iterations to get working (transistor and capacitor replacements)

Bias values:

SA-550 original
L +5.9 R +7.9

SA-550 biased
L +4.2 R +4.3

SA-850 original
L +17.1 R +13.2

SA-850 biased
L +4.5 R +4.6

The video contains the SA-550 adjustment with a demo at the end of both. Unfortunately, the SA-850 video did not record! I’m posting the screenshots from the service manual for each in the comments. 

Feel free to reach out to me on these models or anything else bias related.