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Thread: Radford Revival activity blog

  1. #71
    Join Date: Apr 2012

    Location: South West of England

    Posts: 206
    I'm Will.

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    Today I designed / made an adaptor to use modern PCB mount radial components in place of the huge quad section capacitor found in SC22 preamps. Should make servicing them in future a lot less of a hassle.

    It fits on pillars that mount on the holes for the original capacitor clamp.

    Radford Revival
    www.radfordrevival.co.uk

  2. #72
    Join Date: Apr 2012

    Location: South West of England

    Posts: 206
    I'm Will.

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    Unfortunately I have neglected this thread a bit. I have many pictures to post though/

    I don't think I've ever posted any pictures of those Kerr amps once they were fully completed

    I took artistic license and made some Kerr logo blanking plates to cover the voltage selectors on the mains transformer and hard wired the voltage internally. The original selectors were damaged and a bit dangerous. I took a photo of the accompanying preamp and vectorised the logo in Illustrator and generated a CNC programme from it.

    These aren't even the final pictures, the input wiring was shortened at some point so it wasn't hanging in mid-air. I had some better completion pictures but I'm not sure where they are.

    The final amps ended up being absurdly quiet, in fact if you shorted the input you flat out couldn't hear ANYTHING from a connected speaker even with your ear touching it. If you left the input unshorted you could hear a TINY bit of hiss - possibly from the resistors of the input biasing network?!

    I recall the distortion being pretty decent too - something like 0.05% at around 9W/ 1Khz /8 ohm. Output impedance was 0.3 ohms in the mid-band rising slightly at either extreme. Distortion at 1W was stupid-low.

    The owner was very pleased! More stuff to come.







    Radford Revival
    www.radfordrevival.co.uk

  3. #73
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,529
    I'm Alan.

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    Beautiful work

    They are brand new amplifiers made with a few reclaimed vintage components
    Firebottle - for the no bottleneck approach.

    I love Hendrix for so many reasons. He was so much more than just a blues guitarist - he played damn well any kind of guitar he wanted. In fact I'm not sure if he even played the guitar - he played music. - Stevie Ray Vaughan

  4. #74
    Join Date: Apr 2012

    Location: South West of England

    Posts: 206
    I'm Will.

    Default

    Quote Originally Posted by Firebottle View Post
    Beautiful work

    They are brand new amplifiers made with a few reclaimed vintage components
    Many thanks They are indeed!

    I found the better pictures of their final state, I will post these be done with it as I'm sure they are getting boring by now

    I have of course done loads of things since these and will post something different soon.















    Radford Revival
    www.radfordrevival.co.uk

  5. #75
    Join Date: Apr 2012

    Location: South West of England

    Posts: 206
    I'm Will.

    Default

    Did a bit of FM tuner alignment today. Had a Radford FMT2 (one of a few tuners we have in at the moment) who's discriminator wouldn't properly centre on 10.7Mhz - no adjustment to the top slug would bring things into line, anything close to 10.7Mhz would give a horribly asymmetric output. I could get a reasonable response if I aligned all the IFs to around 10.58Mhz but that is not ideal as that's not then aligned to the IF output from the front end (though it still tuned quite nicely)

    Adjusting the lower tuning slug in the detector transformer (corresponding with either the primary or secondary, I wont be dismantling the can to find out which!) seemed to do the trick. There is no access hole in the PCB so you have to tune the bottom one through the top one with the correctly shaped tuning tool. The top slug was pretty loose so a couple of layers of PTFE tape around it tightened things up nicely while still being smooth to turn.

    Got a pretty good detector response zero crossing bang on 10.7Mhz, the envelope looking pretty good but was not tweaked for best appearance but best looking detector output (at varying drive levels into the IF strip to ensure symmetry and linearity over a range of signal levels)

    Got a very nice looking S-curve in the end!


    Radford Revival
    www.radfordrevival.co.uk

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