Sansui 500A

The 500A model was in some respects unique for Japanese-made receivers and had very characteristic features for this design:     the driver tubes were 6BL8 / ECF80 / ECF82 - this is an exception, because in Japanese products the driver tubes were 12AX7 / ECC83 or 6AN8,     the stereo indicator was the change of the highlight color of the tuning indicator from white to green. It was executed by a two transistor circuit,     the receiver has no extensive channels, reverse and mono / stereo switches,     phono correction preamplifier (and for the tape head) was based on four silicon transistors,     the receiver has a very modern design, even going back to the 70's. The Sansui 500A looks very nice. Green backlight of the scale, additional colored lights informing about the selected PHONO / TAPE / POWER function add elegance to the device. The front panel is thick aluminum in the lower part, galvanized in a specific quasi salmon color. A metal frame around the front. The receiver was factory-prepared for mounting in a wall or console (and this was also included in this frame) and was sold with an assembly diagram. Hardware knobs were also new to Sansui, a decent thick and hard plastic with aluminum endings. The electronic 500A is a structure with some interesting features.     a sensational FM head based on ultra-modern tubes at the time - two 6CW4 nuvistors and one ECC85. Sensitivity and separation almost referential and boldly comparable with the best products of Scott and Fisher,     perfect MPX decoder on three lamps,     preamplifier in band control circuits based on the ECC85 tube (as in the SM-3xx, 500 and 250 models). The power amplifier works in a Push & Pull configuration with 7189A / EL84 tubes. Tubes worked with fixed bias and it was possible to set this parameter separately for each tube. It was enough to add a resistor, e.g. 1 ohm in the cathode circuit, and by measuring the voltage drop across this resistor, the bias current could be set the same for all tubes. The power delivered by the receiver is simply unbelievable for equipment with 7189A / EL84M tubes. The measured power is 24 watts at a load of 8 ohms and with a frequency response of 25 Hz - 43 kHz! Measurements were made with NOS 6P14P-EV tubes. The amplifier had low distortions.

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