This is my Hitachi HA-6 stereo amplifier.
This amplifier was made around September 1983, making it roughly 27 years old, It won 5 stars out of 5 in the German version of What Hi-Fi.
Specifications
100 Watts * per channel, min RMS, at 8 ohms from 20 Hz to 20 KHz with no more than 0.005% total harmonic distortion (THD)
105 W/ch + 105 W/ch (8 ohms. 1 KHz T.H.D 0.005% SINUS) 100 W/ch + 100 W/ch (8 ohms, 20 Hz - 20 KHz, T.H.D 0.005)
Harmonic distortion (8 ohms)(at 1/2 rated output) 0.005%
Intermodulation distortion (at 1/2 rated output) 0.005%
Power bandwidth 5 Hz - 40 KHz (T.H.D 0.1% 1/2 Rated)
* Measured pursuant to the Federal Trade Commission's Trade Regulation Rule on Power Output Claims for Amplifiers.
This is stated on the service manual.
Features.
Liquid / gas cooled heat sink (heat loop) which the final output stage transistors are bolted to.
7 second delayed power on so that the power supply can stabilize before the speakers are connected via relays, saves speakers from the power on "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 transistors from self destructing / 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, I have had it do this once in it's life and that was on a hot day and a very loud party!
Two 12,000 Microfarad @ 63 volt DC capacitors these are roughly the same size of a can of Coke, and are the main smoothing and reservoir caps for the main power amp. 126 volts DC sits across them and this is at about 10 Amps so quite meaty!
This amplifier is of the DC coupled push pull design with a set of transisort for both the negavive and positive half of the sound output stage, the this makes it a very powerful amplifier.
The down side to DC coupled design is that if any transistor fails and goes short circuit the remaining end up having 63 volt + or - (depending on the side that failed) stuck up them, these then pop one by one until either the power supply fuse blows or fuseable resistors if fitted blow. This makes it quite costly to repair given it's age and the lack of available parts.
The left channel did go bang once and it cost about £40 for new transistors.
It originally had all green button / power illumination 3mm LED's but these were a bit boring so I fitted blue ones and brought it into the 21st century.
In normal day to day use it never goes above volume mark 3, and 5 is as loud as I can take it before my speakers and ear drum's pop but it goes up to 10
Runs a set of Celestion Ditton 15 XR speakers extremely well.
See the photo's above for pictures of the inside and outside.
