Nikko HB-18005 (inside a STA-1101) - diyAudio
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Old 18th March 2012, 09:18 PM   #1
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Default Nikko HB-18005 (inside a STA-1101)

Hi, yesterday I've got a nice Nikko STA-1101 receiver. Really a strange, massive 40 years old boy, very very well built (wiring apart...), in excellent conditions.
Unfortunately, the right pre-amp channel does not work. I've discovered a faulty IC, labeled "Nikko HB-18005", that is mounted inside the first stage ("Flat amplifier" card, immediately after the volume potentiometer). This component is a 8 pin custom IC, and it's no more available , of course.

I think it's not so complicate to replace it with something equivalent, but neither schematics nor datasheet seem to be available

Anyone has any idea or documentation about ? I've also realized that the power amp transistors have been replaced , and now the right channel mounts two 2SC1030 and the left two 2SD551. Which are the proper ones ?

Thanks so much to everyone

Ciao, Paolo
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Old 19th March 2012, 09:19 AM   #2
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as about the buffer IC you may ID the pins 4 is - V 8 is +V or so, inputs and outputs install a base for the IC you then you can try anything you want starting from 4558 or 5532 ...I would say not to go to anything extreme of the OPA series unless you have instruments and knowledge to verify present oscillation.

For outputs you need obviously to replace only if blown also there you may put anything you like ...example will be MJ150003-4 .... non though will be drop in replacements you need to run bias set up procedure from scratch

All changes need to be symmetric you have to replace both N and P transistors working or not .... both channels also for symmetry reasons

then you need to recap the all amplifier

some info here vintage amplifier repair/upgrade manual
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Old 20th March 2012, 10:09 PM   #3
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Thank you so much Sakis, your interventions are always wise and gentle

In the meantime, I've found in Internet (Analog Alley) the official "IC replacement bulletin" from Nikko, about the subsitution of my HB-18005

It's based on 2 normal npns, and few other components. I'm preparing the PCB

I'll let you know

Thanks a lot again, Paolo
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