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  1. TapeHeadOne

    Available XPL909's and RCA410's

    I know. I still want some.
  2. TapeHeadOne

    Available XPL909's and RCA410's

    I am also in need of some 66546’s to restore my amp to more or less original condition. What could you spare and how much, please ?
  3. TapeHeadOne

    PL400 II Resurrection

    Hello Gepetto I'd made an edit to my post, but it seems to have gone wrong. I was hunting for faults and found Diode 13R to be possibly dodgy. So I replaced it. Of course a wire came off on the other channel but this time I caught it. Trying to bias the right channel I now can't get it under...
  4. TapeHeadOne

    PL400 II Resurrection

    If you are talking about the wires on the bottom of the board that go to the bottom row of transistors on the chassis ( to be like sure, ye ken) yes, and as I'm not sure of anything regarding this infernal box I've redone them, unfortunately to no avail. With great risk to my personal mental...
  5. TapeHeadOne

    PL400 II Resurrection

    Yes near as makes no difference. Ok, fair enough, a higher negative voltage. Pete
  6. TapeHeadOne

    PL400 II Resurrection

    I'm seeing a markedly higher voltage on the E of Q9R. Where Q9L is at -0.1V approx, Q9R is at -0.35V. Drivers in or out, no difference. Pete
  7. TapeHeadOne

    PL400 II Resurrection

    :scratch::banghead::cussing: OK... Starting with the left and right bias pots fully counterclockwise : L Bias : 246 mV R Bias : 115 mV L Bias 2N5088 C-E : 2V R Bias 2N5088 C-E: 1.96V L Bias : 375 mV R Bias : 169 mV at approx the same position L Bias 2N5088 C-E : 2.11V R Bias C-E : 2.11...
  8. TapeHeadOne

    PL400 II Resurrection

    That's what I'm not seeing. 75V comes in through L7 but R35 reduces that. So it must be base voltage. Which points to Q9. But on both channels?
  9. TapeHeadOne

    PL400 II Resurrection

    I made following measurements : Turning both bias pots fully counterclockwise, I measure 240 mV on the left channel, and 120 mV on the right. Setting the left bias at 375 mV, and the right pot in approximately the same physical position, I measure 168 mV, which I kind of expected. Q6 L and R...
  10. TapeHeadOne

    PL400 II Resurrection

    Yes, perfectly. Thanks !
  11. TapeHeadOne

    PL400 II Resurrection

    OK ,after finding yet another dodgy wire I now feel I have made some progress. I used all 15024 on the bottom so as to keep the 66456s of which I have only three left out of harm’s way. I can now once more bias left to 375 mV without issues. The right only gos up to 260, but since it also starts...
  12. TapeHeadOne

    PL400 II Resurrection

    OK, so if I finally get it working to I install 15024/66456/15024/66456 or do I dispense with the 15024 altogether and leave the spaces unpopulated ? Pete
  13. TapeHeadOne

    PL400 II Resurrection

    The transistors on the amp are all still measuring OK. Would it be acceptable to replace the 66546 with MJ15024 while I'm trying to figure out what's going on ? Those 66546's are hard to xome buy, and If I toast them I'll be set back for months. I'll put them back once I have it figured out...
  14. TapeHeadOne

    PL400 II Resurrection

    Plus and minus 15V present and accounted for !
  15. TapeHeadOne

    PL400 II Resurrection

    Lights out Here. First thing tomorrow !
  16. TapeHeadOne

    PL400 II Resurrection

    2n5088. Pins swapped.
  17. TapeHeadOne

    PL400 II Resurrection

    What would cause 70+V on the C-E of Q6 L+R ?
  18. TapeHeadOne

    PL400 II Resurrection

    I have now restarted in earnest. I have replaced the 2 bias transistors that now had broken legs from the many manipulations. I replaced a suspect wire, reassembled the amp and switched it on. Remarkably, no fuses blew, and no smoke was immediately obvious. Upon measuring the Left and right bias...
  19. TapeHeadOne

    PL400 II Resurrection

    My backlog seems to have cleared up somewhat, so this weekend I will once more try to resuscitate the beast . Pete
  20. TapeHeadOne

    PL400 II Resurrection

    No (and there's only 2A in there), but it ate the 2 MPS 651s. Yes. BOTH channels. Everything else seems to have survived. Didn't have 651s available so waiting for parts. I'll continue with it when I have time or feel so inclined, which won't be soon. It's taken up far too much of my time.
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