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Thread: Radford STA 12 Rebuild

  1. #21
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 41,264
    I'm Geoff.

    Default

    Going well there Alan. The bracing angles were a good idea. I'm looking forward to seeing how this turns out.

  2. #22
    Join Date: Oct 2017

    Location: West Wales

    Posts: 73
    I'm Alan.

    Default Nearly there...

    ... well it has taken a while.

    I started this back in 2017 and have had several more 'false' starts to get it completed. So having cleared everything else it was time to concentrate on finishing the old Radford.
    It is an STA12 which is a very close relative to the original STA15 (EF86, ECC83 and EL34 etc.)

    Recapping a little (Tinypic is closing soon so the original pictures might vanish soon...), the first problem was someone had modified this amplifier in a very unsympathetic manner, then the chassis was distorted due to the much flimsier metal used on these models. This distortion then leads to the component boards also bending and so on.





    Excellent work here, not.







    I previously reinforced the chassis plate and 'reverse engineered' the component boards from an original STA15 diagram and a couple of rare STA12 photos on the net. That and a few obvious, and some less obvious, differences in the circuit / layout.







    Then my next problem were the output transformers. The new replacements are for the Series 3 STA15 having different output taps to the originals, so required different impedance switching etc. But they fit very well.



    And that is where I had to halt for some time, until last week in fact. So to start with I had to meld the earlier and later impedance switching using the Series 3 as my template.










    Then wire up one of the circuit boards switch on and hope... for the best.
    I was greeted with a low 'far*ing' on initial power up, but reversing the primaries fixed that. Then music at last if only in mono.






    I left it running for an hour or so and all was good. Happy everything was well - on to the other channel asap.










    So there we are, it has been running for a couple of days now and it is an astonishing amplifier. It really does the Radford thing very, very well. So much detail and control all through the volume range and no noise. Not bad for an amplifier made in 1960. Even the mains transformer is much quieter than my STA15 III. It has become my instant favourite.

    Still a few of things to do though.
    First is thank Will at Radford Revival, it could not have happened without him.
    Then it needs a base plate, it came without one and it's on 4 rubber feet at the moment.

    Alan
    Last edited by snowman_al; 26-08-2019 at 06:03.

  3. #23
    Join Date: Jan 2009

    Location: Essex

    Posts: 21,050
    I'm openingabottleofwine.

    Default

    Beautiful work done there Alan. Well done!
    Barry

  4. #24
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 59,146
    I'm Grant.

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    Bravo... Top Job
    Regards,
    Grant .... ؠ

    I've said it before and I'll say it again: democracy simply-doesn't-work
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  5. #25
    Join Date: Apr 2012

    Location: South West of England

    Posts: 269
    I'm Will.

    Default

    Great job, glad to be of assistance with the OPTs and happy it all worked out
    Radford Revival
    www.radfordrevival.co.uk

  6. #26
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 5,095
    I'm Alan.

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    Superb job Alan, that must have taken a good few hours (weeks?).

    Another thumbs up for Will Great to have such committed engineers on AoS.

  7. #27
    Join Date: Oct 2016

    Location: Hampshire

    Posts: 291
    I'm Mel.

    Default

    Another well documented rebuild Alan.

    Your care and attention to detail is amazing - most would be rushing to get the job done rather than doing it properly.

    I'm still enjoying the World Designs KEL 84 you rebuilt and documented in the same manner as this.

    Mel

  8. #28
    Join Date: Sep 2014

    Location: Northern Ireland

    Posts: 1,064
    I'm John.

    Default

    Great to see another of these superb amplifiers resurrected and good for years to come. The Radfords really do seem to be an amp for life as they are so serviceable especially with Radford Revival on hand. Really good stuff
    Naim CDS CD player, BTE Khozmo passive preamp, Luxman Avance Z504 power amp, Lockwood Academy speakers with Tannoy HPD385 drivers, BigBottle Audio Spotfire interconnects.


  9. #29
    Join Date: Aug 2011

    Location: Nottingham

    Posts: 479
    I'm Ian.

    Default

    Quote Originally Posted by walpurgis View Post
    That idea crossed my mind. I'd expect they'd have some spare parts and could possibly match the enamel too for touching in purposes.
    Beautiful work Alan. May I please ask if you got a result on the matching enamel ? I have a 25 in lovely condition but with 2 minor blemishes on the casework I'd like to touch up. Airfix don't seem to do a 'Radford blue' !

  10. #30
    Join Date: Oct 2017

    Location: West Wales

    Posts: 73
    I'm Alan.

    Default

    No sorry I did not. I decided to leave it 'as is' to show some of its age...
    I have a metal plate for the bottom now so will give that a coat of something close from Halfords or the motor factors. It does not need to be perfect, it will be underneath.

    The other thing is that it is totally different in colour to my STA15 III (which is two tone and I guess will be similar to your 25). The closest picture to the real STA12 colour is the 'rear view' (one from last) the white balance on my camera is not the best.

    I have found that the Humbrol (or Airfix) enamel actually can be mixed to match lots of things with a bit of time so that might be the way to go if the areas are not too large or obvious?

    Alan

    PS thanks for the comments everyone.

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