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  • #16
    Here's an interesting article on power transformers. Pity the scan is poor, but you can work it out;
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    • #17
      Morning all,

      It took a while, but I finally had some spare time last week to dedicate to my Oscillator-to-Amp project. Thanks again to all the advice given

      In the end, I kept it simple and opted for the classic Vox AC4 circuit (with the EF86), minus the tremolo but with the reverb circuit from a Vox AC30 shoe-horned in.

      Here's the chassis, stripped out and ready for a new lease of life:

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      I'd hoped to recycle the mains transformer, but at some point along the way it gave up the ghost and was replaced with a Danbury unit from Barry at Ampmaker.
      It was a similar tale with the reservoir caps, which were (perhaps unsurprisingly, given their age) leaky as an old sieve.

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      Naturally, it didn't occur to me to test them until after first switch on, when the amp was emitted a ferocious wail that grew steadily louder until I was afeared for the health my test speaker, not to mention my ears!
      Only after a speedy switch-off, and a thorough review of the wiring and layout did it occur to me that - in spite of appearance - 50 year old Electrolytic capacitors may not be quite at factory spec
      After knocking together a sub assembly from the parts drawer:

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      I cautiously flipped the on switch again, and to my surprise (and relief) it worked perfectly. Happy days.

      Here then is the amp in it's full glory:

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      I'm still waiting on a transformer for the reverb circuit, and the keen eyed amongst you will notice that in the end I added the tremolo circuit too. Sadly, it's not the most elegent addition. I'd been careful with my original layout to keep my wire runs as short and neat as practical, in keeping with the spirit of the original wiring, which was a work of art. By using screened wires I've kept the noise down to a minimum, but it still 'chugs' quietly when the circuit is turned on.
      It sounds great though, I'll upload some sound clips when I get around to making them. The speaker is a 6" Jensen, in an old hi-fi speaker box with the back taken off, and is a pretty good match for the amp.

      There's plenty more photos, some of which I'll upload when I get a chance.

      Matt.

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      • #18
        Gorgeous!
        "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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