170 watts is the consumption of the amplifier. He can not deliver this power to the speakers. I think it should give a big up to one hundred watts total RMS on all outputs, and yet I am very optimistic I think! Anyway, amplifier 20 watts RMS twice and generally ample, see too powerful to listen to music in a salon. To a party, yes, there it is recommended to have an excess of watts! I have a Hitachi HA-171, circa 1976 (with a hybrid of two times 15 watts RMS, shown behind near the AC power cable, a consumption of 80 watts) and already when the meters indicate 1 watt per channel should strongly raise your voice to hear him talk! For the double sense of power (or volume) ears, have to go to 2 times 10 watts, compared to twice 1 watts. So it's all relative, the wattage outputs HP amplifier. Speakers must have good sensitivity, gender at least 90 DB.

The performance data written near the AC power cord is at all times the maximum consumption of the device, including various lighting; LEDs; timer relay etc..

But hey, Hitachi remains a good brand. In addition, the material of this era was built to last in time and not burn out after a few years as it is today! As with all things made at that time, including cars and appliances!