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  1. You can't go wrong using one of the examples from...

    You can't go wrong using one of the examples from the chart that suits your B+.

    Only increasing the plate resistor will increase gain but not plate current or tube dissipation. But it will cause...
  2. Thread: Pickup dying

    by Helmholtz
    Replies
    19
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    594

    I especially distrust lacquer potted Fender PUs....

    I especially distrust lacquer potted Fender PUs. Meanwhile I found 2 such early 70s strat PUs, where the coils completely separated from magnets and flatwork. You can feel the coils shift with a...
  3. But then you'll also need 2 JBL E130-8s. At least...

    But then you'll also need 2 JBL E130-8s. At least that's what he used in 1986 when I had a chance to take a glimpse at his speakers and equipment from very close during a show in a German TV studio....
  4. Don't forget the internal plate resistance (maybe...

    Don't forget the internal plate resistance (maybe 60k for an ECC83 with bypassed cathode resistor) which acts in parallel to the plate load (referring to the current-source tube model) and prevents...
  5. Thread: Pickup dying

    by Helmholtz
    Replies
    19
    Views
    594

    Well you had the chance to get a clue during...

    Well you had the chance to get a clue during disassembly. Did you find the point of wire rupture? Was the PU lacquer potted?
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    Sticky: Are you speaking of the design shown in post#393?...

    Are you speaking of the design shown in post#393?



    Seems that only one of your coils works properly.
    Do you get about the same signal level using each of the coils separately (each in its...
  7. Good point! After all, straight series wiring...

    Good point!

    After all, straight series wiring of rectifier diodes was quite common in the early days when high enough PIV diodes were not available.
  8. Makes sense. That's rather low humidity. ...

    Makes sense.



    That's rather low humidity.


    Seems that some hygroscopic deposit has covered most of your amp's innards. In this case it is very probable that also the board became conductive...
  9. Replies
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    The illustration of the section shows a moderate...

    The illustration of the section shows a moderate flux line density in the the center pole piece (less than in the airgap). This is not in line with the high B values in the center which can only be...
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    Flux (lines') density must be highest where flux...

    Flux (lines') density must be highest where flux carrying cross section is lowest. But as it is a 3-dimensional problem, a 2-dimensional illustration may be misleading.
  11. If it's 120Hz it is not heater hum (60Hz). If...

    If it's 120Hz it is not heater hum (60Hz).
    If you are sure the culprit is the PI socket you should replace it. Or at least remove it and give it a thorough bath in isopropyl.
  12. Thread: Pickup dying

    by Helmholtz
    Replies
    19
    Views
    594

    The Fender (1965) assembly instructions...

    The Fender (1965) assembly instructions prescribed lacquer dipping of the magnets-flatwork assembly before winding and potting, probably in order to stabilize the assembly and insulate the magnets....
  13. Or use single sufficiently rated (1250V/1A or...

    Or use single sufficiently rated (1250V/1A or higher) diodes like BY127/227/133/255 without the caps.

    https://www.donberg.fr/catalogue/semi-conducteurs/semi-conducteurs_bu-bz/page_2.html
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    Yeah, that's what I expected. The behaviour...

    Yeah, that's what I expected.

    The behaviour you describe is typical for beginning saturation. Flux cannot be stopped anyway as there is no magnetic insulator. It can be locally shielded or...
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    Thanks. I just figured it would require more...

    Thanks.
    I just figured it would require more than doubling magnet weight to double airgap flux density using low carbon steel, as pole parts would be in "partial saturation" at least above 1 Tesla.
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    Out of curiosity: Are airgap flux densities in...

    Out of curiosity: Are airgap flux densities in excess of 1 to 1.5 Tesla efficiently achievable using low carbon steel (1006 to 1010) pole piece material or would this require something like "pure"...
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    It makes a difference if legally guaranteed...

    It makes a difference if legally guaranteed vacation days are taken in a planned/organized way spread over the whole year or if most export/import business is interrupted for up to a whole month (as...
  18. This is certainly true for the JTM45 with GZ34...

    This is certainly true for the JTM45 with GZ34 tube rectifier, KT66s and (non-optimal) 8k plate-to-plate impedance.
    But its successor, the model 1987 (introduced around 1967), employing EL34s, SS...
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    I think this depends if you and your country can...

    I think this depends if you and your country can afford it. Italy can partly compensate with increased touristic business in August. Nevertheless its economy is down.
  20. As the voltage across the diodes is pulsed,...

    As the voltage across the diodes is pulsed, capacitors > 10nF will do the voltage sharing job. Merlin also mentions the option of using high value resistors, but 1kV rated caps are much easier to...
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    It is an Italian tradition called "Ferragosto"....

    It is an Italian tradition called "Ferragosto". Many companies close down in August for at least a couple of weeks as well.

    I think origins are partly religious and partly practical: It gets very...
  22. I think it is easier to understand max. PIV (peak...

    I think it is easier to understand max. PIV (peak inverserve voltage) across the diodes if you ignore the CT and ground reference as they don't change the voltage across the diodes.
    The RMS voltage...
  23. Don't forget the influence of the speakers....

    Don't forget the influence of the speakers. Marshall always used Celestions while Hiwatt mostly used Fanes AFAIK. Fanes sound way different from Celestions. I once had a Vox AC50 with Fanes and could...
  24. Don't think they would have been the same without...

    Don't think they would have been the same without mad Keith Moon.
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    Yes, see posts # 11,17, 26.

    Yes, see posts # 11,17, 26.
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    A DCR difference between primary halves of up to...

    A DCR difference between primary halves of up to 20% is not unusual (depending on winding/interleaving scheme). But the AC voltages on both halves must be identical.
  27. I was there amongst around 600,000, saw the...

    I was there amongst around 600,000, saw the concert and was overwhelmed by the sheer power of the Who. I always thought they were the most dynamic and powerful rockband I ever saw. The only other...
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    I would - make sure that the speaker out...

    I would
    - make sure that the speaker out switching jacks work properly
    - disconnect all OT leads and do a neon bulb test.
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