This Pioneer SX-750 Stereo Receiver came through the shop recently for an overhaul. It had been stored in a basement for a few decades before the owner decided it was time to clear out and refurb some gear.
This is an upper midrange receiver with AM and FM tuning, aux and phono inputs, and 2 tape deck inputs with dubbing capabilities. It offers 50W per channel at 8 Ohms, or 60W at 4 Ohms, with <0.1% THD+N ratio and a slightly expanded frequency response.
This stereo got all new electrolytic capacitors throughout.
Time to clean it up! This model also got a full FM alignment. The dial was off by about 1 cm previously, but cleaned up perfectly. This SX-750 had very good, clear alignment instructions in the service manual and the adjustments were very easy to make; the FM comes in spot-on perfect now. The DC offset on this model was about 5 mV, and is not adjustable (it is set by the careful matching of the differential input pair to the final amplifier module.) Idle current adjusted perfect to 30 mV.
Time for performance testing! The service manual gave quite a few data points.
Perfect frequency response through the main audio range.
The unit misses the full extended-range frequency response by a hair, falling off at closer to 30 kHz than 50 kHz. That’s past human hearing in any case, though.
The phono input’s RIAA curve is almost perfectly matched.
The SX-750 passes its distortion specifications at all power levels given in the manual (1W, 25W and 50W).
With all this service, this Pioneer SX-750 stereo receiver is good as new! It should sound great for a long time to come.