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Look what's arrived for repair ... VOX V-125 Lead head

Discussion in 'Amp Tech Center' started by Jon Snell, Oct 21, 2020.

  1. Jon Snell

    Jon Snell Tele-Holic

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    Not too often does a truly lovelly piece of English heritage turn up for repair.
    This will be interesting to refurbish. Dates back to circa 1973. The electrolytics have date codes 7323 meaning 23rd week of 1973, the main smoothing capacitors however, look original and are dated 10-81 so October 1981.
    After removing the chassis from the case, I evicted the wildlife, spiders and their webs. They now have a new home eating any flies in my workshop, so they will be hungry!
    There are four EL34s made by Mullard and as these amplifiers run quite cold, I wouldn't be surprised if they were all reading good on my AVO VT163 valve tester and µ reader.
    There are two ECC83s missing, probably were Mullard and sold on fleabay at an extortionate price I shouldn't wonder.
    There is a fault description of, "Clicks and bangs" which could mean anything at this point.

    To be continued as I progress. Thank you for your interest.
     

    Attached Files:

    Last edited: Oct 22, 2020
  2. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Fun - I'm getting a '64 AC30 dropped off in a few minutes here
     
  3. Mad Kiwi

    Mad Kiwi Friend of Leo's

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    How has it survived in such good shape not being handwired?

    ;)
     
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  4. secretsoundz

    secretsoundz TDPRI Member

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    Very cool, that's not an amp you see too often.
     
  5. ScottJPatrick

    ScottJPatrick Friend of Leo's

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    1973? I remember buying a new Vox V125 in about 1983, think they only came out a year or so before then. Can't remember much about it apart from the fact it didn't sound anything like an AC30 but was bloody loud! Wanted to buy the 2x12 Climax combo but couldn't find one, glad I didn't. You can see it in the background here, on top of a Marshall cab and just in front of the home brew! guitars0014.jpg
     
    Last edited: Oct 21, 2020
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  6. tubegeek

    tubegeek Friend of Leo's

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    Looking forward to LOTS of gutshots - and maybe its own thread?
     
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  7. Bulldoggio

    Bulldoggio Tele-Meister Gold Supporter

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    I used to have one of those. Crazy powerful, great EQ, but none of that Voxey chimey character.
     
  8. Jon Snell

    Jon Snell Tele-Holic

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    Very surprising as the board is Paxolin and is showing signs of heat marking around the phase splitter anode load resistors.
     
  9. Jon Snell

    Jon Snell Tele-Holic

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    Probably NOS capacitors were used as the main smoothing capacitors are dated 1981. The customer has the original 2 x 12 speakers and cabinet in immaculate condition.
     
  10. Jon Snell

    Jon Snell Tele-Holic

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    Day two.
    A visual inspection is paramount before work is carried out.
    Spot the immediate issue ... Screenshot 2020-10-22 at 14.06.36.png Why is the first EL34 not in like with the other three?
    That was because the spiggot was broken off so it could be placed in any direction!

    Everything else looked OK, main smoothing capacitors were within specification and the worsed one had a 7uA leakage which is absolutely no proble.
    I made a list of components required which included one 3.15A T mains fuse to replace the 5A that was fitted, two 4uF 350volt, one 100uF, two 4u7 35volts and one 125u 35volt electrolytics plus one 22k 1W, one 56k 1Wand one 47k 1W. Then there was the issue with the phase splitter.
    After fitting an ECC81 I noticed the crackle when powered up. This was the socket itself. Too much abuse over the years.
    Screenshot 2020-10-22 at 13.38.41.png New ceramic socket fitted. Screenshot 2020-10-22 at 13.39.27.png

    That cured the crackle and the new 100u capacitor cured the poor bias, incidentaly, the schematic is drawn wrong but as it is only four components, not worth re drawing.

    This Vox works and sounds just like the Marshall is was designed to mimik.

    Screenshot 2020-10-22 at 13.40.21.png Screenshot 2020-10-22 at 13.40.44.png Screenshot 2020-10-22 at 13.41.30.png Screenshot 2020-10-22 at 13.42.03.png

    Using an ECC81 phase splitter, the capacity is there to drive the four EL34s into class Ab2 and possibly get the full 125Watts of power!
    I replaced the mouldy sleeving. The mould was dried Hellerine oil that had got damp so nothing nasty.
    Screenshot 2020-10-22 at 14.04.37.png
    I hope you enjoyed this rebuild and repair.
    Thank you for looking.
     
  11. bettyseldest

    bettyseldest Friend of Leo's

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    Reminds me of sessions at home in the early 70's. Dads 25 pint homebrew barrels rapidly emptying. A single microphone plugged into the aux input of Dad's Yamaha electronic organ, our Antoria, Columbus and Vox guitars all into my RSC Phantom 50 combo, but we did all own guitar leads and straps.
     
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  12. TwangToInfinity

    TwangToInfinity Tele-Afflicted

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    beautiful thank you for the pics!
     
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  13. tubegeek

    tubegeek Friend of Leo's

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    @Jon Snell this what you're looking for?
    Found on my floor this morning: more investigation required. And epoxy.
    20201022_113740.jpg
     
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  14. Jon Snell

    Jon Snell Tele-Holic

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    Yep. Just the job!
     
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