This is my other Hitachi HA-3 stereo amplifier.
I bought this on eBay for 99 pence in November 2006, it was faulty with no indication of what was wrong in ebay listing.
Found out that it powered up but had no sound at all, then soon found that the left channel amplifier chip (an STK4042XI) was short circuit from the power supply +Ve input to sound output pins, this caused the speaker protection to deactivate a relay disconnecting the speakers so they would not fry!
I managed to find a replacement chip and fixed it for around £12.
The amplifier I believe was made circa 1985 thus making it around 22 years old, It boasts 80 watt RMS (Root Means Squired) 240 Watt PMPO (Peak Music Power Output ) into 8 Ohm load per channel.
Features.
Similar to my HA-6 but it has a few less switches and push buttons, they are both the same width but the HA-3 is shorter and weighs less than the HA-6.
7 second delayed power on so that the power supply can stabilize before the speakers are connected via relays, saves speakers from the thump noise.
Short circuit protection, as soon as any output is shorted to ground the sound "cuts off" (relays switch off) and stays off until the unit is powered down and back on again, saves the output transistor from self distrusting / driving into a dead short!
Heat protection, using a thyristor of all things, but it works, if it gets too hot it does the above just cuts off.
Two 10,000 Microfarad @ 63 volt DC capacitors these are roughly 1 1/2 inches in diameter and 3 inches long, and are the main smoothing and reservoir caps for the power amp. 120 volts DC sits across them and this is at about 6 Amps so still quite meaty!
This amplifier uses a SANYO STKxxxx series "amplifier in a chip", these are used in allot of Pioneer, Sony, Aiwa and Sanyo equipment as they are cheep to make, generally reliable and are still capable of sticking out quite a bit of power!
This means that very few other components are needed in making this amplifier (if you compare it to the HA-6) and also makes it easier to repair.
The other good thing is that virtually all the transistors are in one chip, it saves you having to test them one by one, as I had to do on the HA-6, also they all get changed at the same time so all should be 100% good and not on the edge of blowing up!
Runs a set of Celestion Ditton 15 XR speakers extremely well.
See the photos above for pictures of the inside and outside.
