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VOX Super Continental Divider Questions

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    VOX Super Continental Divider Questions

    Hello all,
    I am the proud new owner of a 1967 VOX Super Continental V303E. It's got a few bad divider transistors, and I'm trying to figure out which ones I need. It seems like there isn't as much information on the Thomas Organ ones versus the UK ones.

    Does anyone know which ones I would need?

    Thanks,
    Jon

    #2
    Before changing any transistors, have you tried changing the "bias" control on the offending tone modules to see if it helps? Mine had several that weren't working correctly, just tweaking these controls was all it needed.

    And, congratulations on your new baby 8)
    Tom in Tulsa

    Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

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      #3
      I did try the Bias. It helped out the C generator, but not so much for the others. What it's doing is a note will be dead, then all octaves below that note will be dead as well. Or I have some notes that just aren't being lowered in pitch.

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        #4
        Okay, so I went back in and adjusted the divider biases again, paying closer attention. It made a lot of progress. I sorted out most of it. All that remains is the bottom two D notes are still out, and all but the top two G# notes are out as well.

        So possibly those are my divider issues and the rest was bias? Still kinda learning as I go. Anyone know which transistors these use?

        Thanks,
        Jon

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          #5
          Good to hear it's coming to life. While searching for parts for mine I did find a place that had those transistors, for about $8 each (!) Problem is, at the moment I don't remember who, I will try to find them again. FWIW, I read claims that the transistors can be replaced with ordinary (cheap) silicon transistors, and another plan "b" to restoring a messed up divider module is to stick a divider chip (CD4024) on the back of the board to perform the actual dividing and you can leave the original parts in place for looks. I bought some 4024s and some 2N3906 transistors but haven't tried them because my dividers started behaving themselves.
          If you are missing the upper octave of a note but the lower are working, that may be a bad connection between the module and the circuit board it plugs onto. You can see there is a row of fork-shaped contacts riveted to the end of each tone module which mate with contact pads on a gaggle of vertical circuit boards. Any dirty/bad connections here could cause the loss of a tone.
          One thing I did was to use a guitar amp as a signal tracer, touching those contacts to test for the presence of the tones on each module.
          Last edited by tpappano; 01-16-2020, 07:45 PM.
          Tom in Tulsa

          Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

          Comment


            #6
            Hi Tpappano,
            I removed the G# module and checked those connections. As far as I can tell, they seem to be okay, though I like your idea of a signal tester. Might have to make one of those.

            One thing I did notice is that on that card, adjusting the bias pot made absolutely no difference. All the way down, all the way up, it always behaved the same. All the other notes, if I went too far, it would cut out or get erratic. This makes me suspect the bias pot. Perhaps it has failed and is giving a bad value to the dividers. The interesting thing is this pot has already been replaced.

            However the organ is old enough that even the replacement may have failed, particularly if it wasn't of good quality. I'll have to see if I can find a way to measure the resistance of the pot in different positions.

            I've tried to find a schematic online, but so far I can't find one that lists the value of that pot, or gives any info on the divider transistors. The work continues...

            -Jon

            Comment


              #7
              I found this schematic online. If I understand this right, it looks like it's a 250 ohm pot. Am I interpreting this right? What else would I need to know about the pot?

              EDIT: A quick google pulled this up from vintage vibe. I need to order a few drawbar end knobs anyway, so it looks like I can do one stop shopping.

              https://www.vintagevibe.com/products...-card-bias-pot

              Comment


                #8
                I bought some drawbar knobs and key bushings from them and I *thought* they were who had the transistors, but I didn't see them when looked yesterday. I guess those cheesy little pots are problematic since they sell replacements. I actually bought an 'official' set of model-specific schematics, I can check tonight on the pot resistance but they probably are 250 ohms. Nothing special about it other than physical size.
                Tom in Tulsa

                Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

                Comment

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