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Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all products

    PAS-3X problems after complete rebuild


    Posts : 4
    Join date : 2008-12-25
    Age : 68
    Location : Umea, Sweden

    PAS-3X problems after complete rebuild Empty PAS-3X problems after complete rebuild

    Post by Swede52 on Sat Feb 21, 2009 6:52 am

    Hi all. I have bought new boards to my PAS-3X and use them together with the SDS power board. I most likely have a wiring problem since my voltage chart looks like this (original Dynaco values in brackets). Line voltage is 234V (not 240) which, IMHO, should explain the slightly lower voltage in some cases.

    12X4 (pin number first):
    1. 298VAC (335)
    2. 0V (0)
    3-4. 10.3VAC (10.5)
    5. 0V (0)
    6. 298VAC (335)
    7. 381VDC (405)

    That seems reasonably OK, doesn't it?

    PC-6 (either 12AX7-VDC!):
    1. 96.2V (115)
    2. 0V (0)
    3. 0.68V (0.7)
    4. 0V (0)
    5. +-11.7V (11)
    6. 124,7V (135)
    7. 0V (0)
    8. 0.74V (0.Cool
    9. +-6.0V (5.5)

    That also seems to be no real catastrophe and the deviations I guess are caused by the slightl low voltage at 12X4 pin 7. Do you agree?

    But here's the big problem: PC-5 (either 2AX7-VDC):
    1. 230V (175)
    2. 64V (0)
    3. 64V (1.45)
    4. 0V (Less than 1V)
    5. +-11.7V (11)
    6. 220V (200)
    7. 40 (0)
    8. 65V (1.25)
    9. +-6.0V (5.5)

    If ANYBODY has a clue to what might be wrong I would be most grateful to receive your help.

    Bo Gustavsson
    Umea (northern Sweden)
    Bob Latino
    Bob Latino

    Posts : 2960
    Join date : 2008-11-26
    Location : Massachusetts

    PAS-3X problems after complete rebuild Empty Re: PAS-3X problems after complete rebuild

    Post by Bob Latino on Sat Feb 21, 2009 2:45 pm

    Hi Bo,

    Usually a wrong wire to the wrong place is not the issue in something like this because a mistake like that stands out like a sore thumb is easy to pick up on a quick visual inspection. It's more often than not a bad solder connection somewhere on the your new PC-5 board. The easiest thing to do is first inspect all the solder joints on PC-5 with a magnifying glass and then REsolder any of the joints that look suspect. You may just want to REsolder ALL the joints on that board just to be sure. Sometimes a solder joint may LOOK good but in reality it is only making a partial (and highly resistive) connection.


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