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Rodger 750BE instant upgrade - generals added!

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  • Rodger 750BE instant upgrade - generals added!

    I had recently posted asking whether or not the 750B could have two additional generals added based upon the fact that there was a clearly labeled section on the capture memory board for general 9 and 10, but with all component spaces vacant. On a hunch, I decided to try and add these two additional generals (4 actually, as there are two memory levels) by populating the uninstalled components. Keep in mind that this model came with 8 generals per memory level from the factory.

    So, I installed the following:

    8 small signal diodes
    2 10k 1/4 W resistors
    2 120 ohm 1/4 watt resistors
    2 2SC2320 transistors (these crossed to the Rohm R166 used by the factory, and I had them on hand)
    1 MM74C08N quad 2 input and gate (NOS picked up from a component liquidator) in a 14 pin DIP socket.

    Then, I temporarily moved the wiring for the piston inputs and lamp outputs for generals 7 and 8 to the corresponding positions on the foil side of the board for generals 9 and 10 respectively. Turned on the organ, set a new registration to both pistons and guess what - the additional generals set and recall exactly as would be expected. Piston lamps also work correctly.

    What is interesting to me is that the RAM on this board consists of two 6508 1K 300ns static RAM chips, out of a possible four (two locations are unfilled) so there is clearly no limitation of the factory RAM to hold the data for two additional registrations. With 2K of storage total, I wouldn't think there would be. I suppose that a larger instrument (i.e. three manuals or many more stops) would have required the added RAM chips - and the manual alludes to this - but looks like I am in business as-is.

    Now I just need to get the 9 & 10 lighted pistons, additional toe studs and engraved plates to label them with. Add a bit of wiring and drill the piston rail and knee board and install new switches, and I'll be upgraded to 10 generals per memory, 20 total. This was easy enough that I am considering adding divisional pistons as well as the board supports up to 6 per division, stock configuration being only 4 per.

    All in all, I am quite satisfied with the results. Next big thing will be to add MIDI, though that will be a much larger scale project.

    Kevin

  • #2
    Amazing! Keep up the good work and keep us posted.
    John
    ----------
    *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

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