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Victor SEA-50 graphic equalizer restoration

Victor SEA-50 graphic equalizer restoration
Few weeks back I got Victor SEA-50 stereo graphic equalizer from one of my friend. This is 10 band stereo graphic equalizer manufactured by Victor Company of Japan (now JVC Kenwood) around 1970 – 1980. SEA-50 consist with 63 transistors and it provides ±12dB control range for 32 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 12 kHz / 16 kHz / 20 kHz center frequencies.

The SEA-50 which we got is not working properly and most of its controls may generate distortion above +8dB and below -8dB. Apart from that left channel of this receiver has low volume and distortion.

Defective transistors in control board (next to 2SA493).

After few hours of checkup we identify few defective transistors (2SC982) in control board and we replace those with 2N3904 NPN transistors. Subsequent to this fix, all controls of SEA-50 start to work again on its full range (±12dB) by without producing any distortion or clipping.

Slider control array and control board.

To fix the left channel we replace few electrolytic capacitors in input/output preamplifier stage of SEA-50 graphic equalizer. We use ESR meter to identify faulty capacitors of this unit apart from preamplifier we replace few smoothing capacitors of PSU which we think defective.  

In this unit majority of external connections are made with wire wrapping terminals and we use appropriate wires and wire wrapping tool to rewire this unit. These sorts of connections are quiet common in old Japanese electronic equipment and previously we did similar sort of wire-wrapping work for some National and Sanyo audio equipment.

PSU and preamplifier stage of SEA-50 unit.

After above fixes we test this unit and it produces excellent results. Audio quality of this graphic equalizer is outstanding and it produces very soft sound with most of the power amplifiers and audio sources.

Following all electronic fixes we clean and repaint this unit to restore its original shape. The final view of restored SEA-50 graphic equalizer is available in here.

Final view of restored Victor SEA-50 graphic equalizer.

Schematic and user manual of JVC / Victor SEA-50 graphic equalizer is available at hifiengine.com for free.

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