Recent content by J M Fahey

  1. J M Fahey

    .68uf presence cap. Help me read this schematic!

    In practice all 4 possibilities: * .68uF * .47uF + .1uF * .56uF + .1uF and plain * .47uF end up being the same, because respective "turnover" frequencies, meaning "where they start to work" are: * 49.8 Hz * 59.4 Hz * 51.3 Hz * 72 Hz because guitar lowest frequency is about 82 Hz, so ...
  2. J M Fahey

    Deluxe Reverb Speaker

    Maybe because it`s *expensive*magic :( And don`t get me started on *weight* :( But if you can move it around (or have muscular roadies ;) ), go for it.
  3. J M Fahey

    .68uf presence cap. Help me read this schematic!

    Well, if you want to have your cake and eat it, you can add a small unobtrusive toggle switch to the front panel (think a pickup phase switch type), leave the original 0.1 uF cap in its place and at will add a 0.47uF cap in parallel with it when you want to. Original schematic: So called...
  4. J M Fahey

    Unwanted Harsh Distortion Please help!

    To really know first what is happening and then where, you (or your Tech) will need scoping it. Otherwise it´s just guessing.
  5. J M Fahey

    .68uf presence cap. Help me read this schematic!

    Weird. I suppose you replace the .1uF presence cap by a .68uF one? Not sure I´d like it because it defeats the Presence control effect , but fwiw and for those who want to know what it actually does: * power amplifier has an "X" amount of gain by itself * said gain, called "open loop gain"...
  6. J M Fahey

    JBL D120 Clones?

    Yes, and VERY good ones. In fact, many in the know chose these because they were still made "like old JBL" while originals had changed: https://www.usspeaker.com/beyma%20liberty-1.htm fact is Spain was economically isolated from the rest of the World (very high Tariff barriers) for decades...
  7. J M Fahey

    Marshall Footswitch alternative?

    You might rehouse it since it´s really simple or get the schematic (or "lift" it from your current one and build a clone, again in a smaller box. If you are not into DIYing, maybe a friend is.
  8. J M Fahey

    Installing Speaker Out Katana Air - Need Help

    Chiming in late, better than never ;) 1) as mentioned above,NEVER EVER join 2 amplifier *outputs* together. Guaranteed damage/destruction 2) do not conside even negative/black wires common. VERY probably each channel uses a bridged/balanced output which means BOTH "+" and "-" wires are HOT...
  9. J M Fahey

    Old Mustard caps possible problem ..... have a look!!

    THAT is an important point,which overshadows lesser or even imagined ones such as Mojo or appearance. Personally don´t much believe the "plastics inside getting mushy" theory, not much cause for degrading in the dark, isolated from atmosphere inside a hermetic epoxy cover, instead just think...
  10. J M Fahey

    Is this speaker ok to use?

    The Glues Direct stuff is the real thing and same as roofing sealant, only thicker. Quite surprised at Dr D´s suggestion because Celestion itself never ever uses diluted PVA (which quickly dries, forms a whitish harder surface skin and has NO tacking whatsoever) as speaker doping but the...
  11. J M Fahey

    Shocked when touching attenuator, already ruled out the outlets. What’s next?

    An OT *is* an inductor, conceptually not different from a car ignition coil or a TV flyback. No big deal if a speaker load is connected because it will absorb amp output energy but if disconnected high flyback voltage peaks appear. High enough to shock you at the speaker side and thousands of...
  12. J M Fahey

    Proco 'lil' Rat

    You are right. Just checked: Mouser does not even name it, Digikey states "Obsolete - no date available" No doubt Boutique/Hobby suppliers can offer some, maybe up to 100 or 200, but no established Factory can depend on that.
  13. J M Fahey

    How to clean a dirty speaker?

    No. If anything, it will sink it deeper, while now it´s only surface gunk. You can "wash it off" meaning like with anything dirty, water softens dirt and something mechanically removes it. Not garden hose or dish washer level water, of course, just the absolute minimum I regularly clean dirty...
  14. J M Fahey

    Is this speaker ok to use?

    10" Guitar Second coat, half around and full around: 15" Keyboard notice cone is brighter and takes sealant with some difficulty.
  15. J M Fahey

    Is this speaker ok to use?

    I use Argentine products, but will suggest similar ones available un USA, plus a mini application course he he. The first ones you suggest are either a coloured paste, or have fibers or are flammable solvent based; the one I suggest is "as liquid as water", water based, roller or brush applied...
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