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Restoring a VOX Beatle Solid State Super Reverb

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  • Restoring a VOX Beatle Solid State Super Reverb

    Newbie here. Nice Forum! I'm in the process of trying to restore and old VOX Beatle Solid State amp for a friend. First time I've ever worked on a VOX and I must say this Beatle I have suffers from multiple problems most of which have been broken wires, bad electrolytic caps, and prior mods. My specific question is... Is there a decent cross reference sheet for the transistors and diodes? BTW.. special THANKS to member R.G. WOW you have quite a collection of VOX info.

  • #2
    http://www.geofex.com/Article_Folders/Thomas%20Vox/Thomas%20Vox%20Replacements.pdf

    http://geofex.com/Article_Folders/Thomas%20Vox/Beatle%20Preamp%20Boards%20Documentation.pdf
    Who does not know and knows that he does not know - teach him Confucius)
    Who knows and does not know that he knows - wake him Confucius)

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    • #3
      Welcome, and thanks for helping keep this amp out of a dumpster!
      You've already read some of my advice, I think. Replace every cotton-picking electro cap. The wires are your enemy, as you know by now, because they snap off at the least provocation.
      All of the NPN transistors in the V1141 and V1142 excepting the reverb drivers and power amp transformer driver can be replaced with a 2N5088 or 2N3904, taking careful note of the different pinout. You can also replace them with 2SC1815, which has the same pin arrangement. If it's a v1143, things get trickier, as the JFETs are not easily available, and modern replacements need some tinkering to get to bias well. The reverb transformer driver and the driver for the power amp driver transformer can be replaced with TO-220 power NPNs; I've used the KSC2073 successfully, although it's a bit light for the power amp driver. Every signal diode can be a 1N4148 or any common silicon diode you have; better to get something working then tweak it in. That's with the exception of the power supply diodes, which need to be at least 100V/3A or bigger. Use MJ150xx series power devices for the power output transistors. A 2N3055 as used in the original is marginal at best.

      If it gets too bad, there is a repair booklet available through The Book Patch for the Beatle. I found that a server "upgrade" has knocked thomas-vox-repair.com off line and I have to go set it up again. If it's too big a disaster, I have a PCB that replaces the entire preamp circuitry for the V1141.

      Yell if you have more questions!
      Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

      Oh, wait! That sounds familiar, somehow.

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      • #4
        Thanks all for the help... R.G. I ordered and received your book " Vox Owners Safety Net". WOW.. lots of great info. I believe the VOX I'm messing with is 1141. It has the onboard distortion and no E tuner. There don't appear to be any FETs. On a side note... I've been putting all the circuit blocks, ie Normal, Brilliant, Bass, Mixer, Limiter, Tremolo, etc. into Microcap 12 (SPICE) and I have been running sims. Pretty cool tremolo circuit. I'm also make an Illustrated parts reference. I will gladly share any info i have when complete.
        THANX AGAIN FOR THE HELP!

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        • #5
          Good work! When I started on the quest, I also put all the stuff into a simulator to get better ideas of what the voltages and currents would be. It was a huge help. I'd love to see what you come up with for illustrated parts.
          On a side note, these amps share with other solid state amps the fact that they get quite hissy over time. I believe that this is because over time the input transistors had their base-emitters broken over by reverse voltage. It's non-fatal to bipolars as long as the power is low, but it does permanently increase the transistor's noise by a tiny amount every time it happens. Over the years, it adds up. The cure is to put an ordinary silicon diode with cathode to the base and anode to the emitter of the input transistors. The diode is reverse biased in normal operation, adding only its reverse biased capacitance. But it conducts on any reverse voltage to the base and permanently prevents reverse base-emitter breakover. For darlington stages like the Beatle inputs, one diode across both base emitters works as well as one diode per transistor.
          Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

          Oh, wait! That sounds familiar, somehow.

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          • #6
            Thanks for the info on the reverse bias diode across E-B of the input transistor. I will definitely do that. Right now I'll be glad to get some hisssssss lol.
            Can I post photos here?

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            • #7
              I think you can post photos. If you don't mind, I'd love to see your photos for future updates to the Vox repair info.
              Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

              Oh, wait! That sounds familiar, somehow.

              Comment


              • #8
                R.G. My email is tstell @ mediacombb.net. Drop me a quick note and I'll send you the photos I'm working on. I haven't had time to figure out how to post photos here. lol..
                Last edited by tboy; 02-05-2021, 10:12 PM.

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                • #9
                  I suggest you delete your email from this public post, unless you like spam. Send it in a PM instead.
                  "Yeah, well, you know, that's just, like, your opinion, man."

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                  • #10
                    1. I am now the proud owner of "The Vox Owners Safety Net" and the "V1141 Beatle Repair Supplement". When I open these it's like opening the Vox bible.
                    2. I have replaced all the electro Caps and fixed several broken wires. The amp now comes on but very very weak sound. I plan to troubleshoot this in the order that is layed out in the V1141 repair supplement.
                    THANX again to member R.G.

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                    • #11
                      ???? Does anyone have any info on THOMAS/VOX preamp circuit board number 25-5236-2? I can't find anything about it and I'm just curious. It's close enough to the others that I still have decent schematics. But it's weird though because the way this one is wired, in the amp I'm restoring, It runs both the Normal and the Brilliant channels through the distortion relay and distortion boost ckt. Perhaps a mod that another tech did years ago? Or was this standard on certain models? No tuner on this one..

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