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Little known Hitachi HA-006

DatunWalnut

DatunWalnut

Active Member
Just fixed this little gem. A Hitachi HA-006 (not HA-6) can't find a damn thing out about it. No service manual, nothing. So I'm very pleased with myself that I have managed to repair and then service it. Does anyone know anything about them? Were they rated in their day? I think it sounds fantastic now. Using an STK 4191ii Darlington pack on the output, it's punchy and lively.
 

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Hi, thanks for replying. No, it's not the the ha-6. Looking at the service manual, it's nowhere near it. I was more telling the story of it and after any info really, though value would be nice
 
Look at the HA-007 model, the model above. A service manual can be found online. I have similar small Hitachi (a.k.a. Lo-D in Japan) units for which the circuit boards inside are the same between the highest and 2md highest model, with components left away in the lower model (and a switch or two). It was common cost saving practice. And if the PCB's are not the same, the circuit is surely not that different.
 

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The HA-007 has a MOSFET output stage, perhaps the HA-006 has a BJT output stage, in which case 24mV across the emitter resistors would be a default bias setting. If it has a MOSFET output stage like the 007, then the 007 manual to be followed.

The input stage and VAS are in a combined STK module; that's the typical Achilles' heal in these designs. Make sure all the power rails related electrolytic caps are fit for service, they will kill the STK otherwise.

There are also fusible resistors in the driver/output stage; they can have changed value

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As a higher model had to offer "more", meaning power, the power rails voltages are likely higher in the 007 model. The simplest way to increase output power.
 
I found quite a few differences between the 6 and the 7 meaning I couldn't follow the diagram for very long. There were similarities (like naming of the ribbon cables and some components) but none meaningful for faulting.tje output of the ha-006 is a Darlington pack - the stk4191ii. I don't even know what power the 6 is supposed to be (though it achieved 42wpc on the bench). Strange that it's so rare.
 
Oh well, the 006 is then a cheap STK version of the 007.
The STK4191II can deliver up to 50W between 35 and 52V volt (designer to decide)

Pin 6 is muting transistor pilot voltage, which should be -5V when muting

See attached datasheet
 

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So my 42wpc isn't too far out of the ball park.
I just find it hard to believe that the whole amp has somehow flown u der the radar for this long
 
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