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Sansui R-50

AM/FM Stereo Receiver (1979-80)

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Sansui R-50


Tuning range: FM, MW

Power output: 45 watts per channel into 8Ω (stereo)

Frequency response: 10Hz to 50kHz

Total harmonic distortion: 0.09%

Input sensitivity: 2.5mV (MM), 150mV (line)

Signal to noise ratio: 73dB (MM)

Output: 150mV (line)

Dimensions: 430 x 147 x 252mm

Weight: 6.7kg


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Audiophile Guide

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Sansui R50

My Sansui R50 has worked flawlessly since 1980. But now I have noticed that the left speaker (Spendor BC1s of course) has what sounds like a bit of 3rd harmonic distortion at low volumes. This leads me to believe that the bias current needs adjustment. The last time I tried this on an amplifier, an Armstrong 626, the output driver transistors blew! The pot was wired badly, only two of the three 'legs' were connected. Now I dont want to blow up my Sansui. So can anyone tell me if adjusting the pots is safe?

Bias Adjustment

in any case, taking the bias down will be safe. you will need to study the schematic and determine at the pot location how it's wired in and which way decreases the bias. Sorry if this is sketchy - but if the aforementioned is out of your technical knowledge, you are best to find someone that can determine this.

It is also a given that one knows the correct value and where to measure it to begin with. the schematic posted here tells me that the adjustment is done at VR07 and VR08, but at a glance i do not see the test points, nor the value. if you can determine this, check the value. if it's within 20% of what called for, hopefully on the low side if not dead on - then go for the adjustment. otherwise i'd suggest looking for a replacement.

My R-50 recently blew one power fuse, then another. checking the transistors i am seeing a failure in one of the outputs - and unfortunately a device that has no direct replacement. until i have the time to come up with that it will be sorely missed.

hope that helps, and good luck -


re: Bias Adjustment

The bias will need to be increased. But I don't know the quality or construction of the pot to know if it is safe to adjust the pot. It is after all 35 years old and a bit cruddy. As I said, the last time I tried this adjustment (on a 626) the wiper lifted off the carbon track and phut! A 100V 1A driver transistor blew. This proved to be very expensive. I rewired the pots so at most it would go 100 Ohms if the wiper lifted.

output bias adjustment

take readings from the "good side" and try to duplicate them on the suspect side.

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