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Thread: Audio Innovations 500 'Reborn'

  1. #1
    Join Date: Oct 2017

    Location: West Wales

    Posts: 60
    I'm Alan.

    Default Audio Innovations 500 'Reborn'

    Well sort of.
    This was my last project valve amp build. I thought you might like to see it?

    I acquired a very sad AI 500 some time ago. An early one with the 'famed' 16 ohm tapped output transformers. I had had a rough life, and hard use. 3 of the EL34s were melted, the cathode resistor and wiring were burnt out as were the droppers...






    My original intention was to rebuild it, but it was a, a mare to work on and b, too far gone. The other factor was its size, just too large for domestic harmony...
    So as I had to strip it down and did not need the phono stage or all those inputs, just how compact could I make it?




    This big, just a touch smaller than a Stereo 20 chassis. Cutting the holes was very hard work with a Q-max cutter, the ally is 3 and 4mm thick!




    But I was pleased with the result.

    T.B.C

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,392
    I'm Alan.

    Default

    Very nicely done

    Are you going to cover the transformers or just have them on show?

  3. #3
    Join Date: May 2010

    Location: Worcestershire, UK

    Posts: 635
    I'm Rob.

    Default

    Nice
    Rob.
    Powered by crossed fingers and clenched buttocks

  4. #4
    Join Date: Aug 2010

    Location: Torquay, Devon.

    Posts: 5,696
    I'm Shane.

    Default

    I actually prefer the AI case.

    S.

  5. #5
    Join Date: Oct 2017

    Location: West Wales

    Posts: 60
    I'm Alan.

    Default

    ... well I wanted to keep as much of the original hardware (ex. chassis) and components as possible. And keep the original circuit of course.
    So I stripped everything down, and tested and cleaned along the way.

    Much to my relief the transformers were all fine. So I gave them a coat of black to match the new chassis.
    The mains transformer had clearly been a later factory replacement, so lacked end bells, which needed a little improvisation to re-instate.








    I took a while to decide on the layout, but finally chose a 'Citation' style, just for a change from the symmetrical format of most of my other amps. And yes everything 'on show'.

  6. #6
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,698
    I'm Simon.

    Default

    Looks good so far. Keep it up.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  7. #7
    Join Date: Oct 2017

    Location: West Wales

    Posts: 60
    I'm Alan.

    Default

    Now for the fun bits...

    I was able to salvage a lot of the original hardware, valve holders nuts and bolts etc. and re-use them.
    Where ever possible I tried to keep the original components too, but apart from the low power resistors and a few capacitors most were 'cooked' and useless. (I'm sure better components were available at the time of manufacture.)



    I wanted to keep the boards too, but in the end only one had survived, then only just. So I had to make tag strip replacements.



    ...and they fit in the front rail of the chassis.



    The only circuit change I made was to have individual cathode resistors and caps for the EL34s, rather than shared. (I reasoned better practice and easy to strap them back together if I wanted to after auditioning.)

  8. #8
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 4,392
    I'm Alan.

    Default

    Excellent work Alan

  9. #9
    Join Date: Aug 2008

    Location: Suffolk, UK

    Posts: 1,335
    I'm Paul.

    Default

    Well that looks much better inside than the original, nice attention to detail. The only criticism I have is that you do not have the obligatory coffee stain on your notebook. A tea stain would have been acceptable.
    ~Paul~

  10. #10
    Join Date: Oct 2017

    Location: West Wales

    Posts: 60
    I'm Alan.

    Default

    Hi Paul, yes I will do better next time. Red wine acceptable?

    Moving on, as I said at the beginning there had been a catastrophic melt down of the cathode resistors and 3 of the EL34s.
    I suspect these might have been a major factor in the problem, all of the 0.47uF coupling caps were leaking, a couple down to the 10s of killo ohms! So much for poly cap reliability... (In fact the only EROs fit for purpose were the 0.15uF ones. The 0.22 and 0.47s were all leaking to some degree?)



    Once rebuilt and new better matched 2 watt resistors fitted, I re-instated it. And time to try it for the first time. Crossed fingers...


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