DIY headphone amplifier
 

PDP8 ! Boy, that's going back a bit. Earliest I encountered was a PDP
11/34A. Had about 512kB of memory spread across 2 boards, AIR. State of the
art for its day. Many hours spent adding / removing NPG jumpers from the
backplane. Happy days ...

I've remembered now, it was in the experimental physics lab; I'd gone
along for an i/v to do a physics degree, and they had this computer
in the lab where they were showing us interviewees some holograms they'd
made. Holograms were pretty hot around then I think, anyway they're
always good to impress students with! I remember the guy proudly telling
me "and here's the computer". This was before I got the 50 quid ZX81 kit
and it was one of the first working computers I'd ever seen - I thought
it was extrememly cool - this was "big science", I half expected to be able
to talk to it like on Star Trek, or at least for it to be some kind of
super-intelligent machine. Anyway I walked round the back to see all the
cables coming out of it (as you do) and spotted an HY50 screwed into the
back panel of the cpu. I have no idea at all what it was doing there,
I think I asked him and he told me but of course the memory has gone.
Most novel installation of an HY50? I wish I could remember what they were
using it for! After all it's an audio power amp so it doesn't make any
sense as an instrumentation amp for an A/D. Perhaps they were driving
something with it under software control? Or maybe they really were using
it as an audio amp and just hooked into the computer's power supply?
It was certainly an odd place to find an HY50!

Yeah, the PDP8 was probably old junk even in those days - I expect it was
an old cast-off they'd rescued from an upgrade! Things don't change
much either - all the UK uni's I've worked in have had a good complement
of old junk machines. I went in one recently and found that they still
have 20 networked 486 machines still in use as windows boxes in the student
lab. Running 3.1. That was only six months ago too.

Tony

DIY headphone amplifier
 

A lot of early computers used an amplifier and louspeaker to monitor various
functions within the processor, etc.
Our Elliott 605 had one.

Maybe that's what they were using it for. But this was something the
user had added - I'm sure DEC didn't build ILP HY50's in as standard ;-)

Tony

DIY headphone amplifier
 

Yes, Tony, they did. ILP paid around 3 a pair as they had (maybe still

I\'m rather impressed. Their amps are better than I thought then.
Those particular hitachi fet\'s were some of only a few types
specifically characterised for audio use, and they gave much better
audio performance than other similar devices. Provided they stuck
to something similar to the Hitachi reference circuit from the
hitachi power fet app note the audio performance would have been
excellent. Shame I never got my hands on one of those MOS modules.

This was mass production for a world-wide market.

I didn\'t know ILP were that big. Certainly the robustness of the
amps I used was without question, they stood up to tons of abuse.

And searching on google reveals - they\'re still going!

link: www.ilpelectronics.com.

There\'s an archive where I found the original data sheets for
the HY50 and HY5.

Tony