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Power supply question

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  • Power supply question

    Why the older models of power supply for MOS-1 organs has the functions: - 5 V Adjust , and + 5 V Adjust, card reader adjust, 27V Adjust ,--but the later models of this powersupply have only card reader adjust and 27V Adjust.
    What do the -5 V Adjust and + 5 V Adjust? And why are this functions not in later models available?

    Regards Chris

  • #2
    By 1969 everybody in the universe was building 5 v supplies. It was the voltage that TTL ran on, and the world ran on TTL. Huge companies were founded, like Power 1, trying to knock Lamda off their perch as the US standard power supply. NASA JSC preffered Lamda with the extra overvoltage clamp board at the time I was installing stuff there (75-79).
    The price of extremely accurate (read B suffix) zener diodes got cheaper and cheaper where it would make no sense to put an adjustment pot on. After all, pot wipers are known to oxidize, and having an adjustment pot just give the circuit a good reason to jump to the maximum adjustment at some point as the pot wiper opened up.
    27 is a bit weirder, not a lot of companies were running 27 volt supplies. I imagine pots were cheaper than 26 v B zeners, and the reliability of 26 v zeners was not as competitively worked out in the marketplace as the 4.4 v ones.
    city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112


    • #3
      How old are these organs? It may have been the release of the 7805/7905 linear voltage regulators the spurred them into eliminating the (expensive!) pots from the design.


      • #4
        They date from the early '70's and precede the IC voltage regulators I believe.

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