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Thread: EQ inductor for old Fender

  1. #1
    Senior Member Enzo's Avatar
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    EQ inductor for old Fender

    I have an old Fender Super Twin on the bench. Complaint is intermittant "graphic" EQ. The 100Hz control has an intermittant inductor. The lead coming out one end moves, and with it continuity comes and goes. SHort of trying to grind the epoxy out of the end in hopes of repairing the part, I need a replacement.

    The part is Fender 011946. Hard to believe, that ONLY 30 years later, Fender no longer lists the part.

    The inductor is 2.5Hy. It is 1" long cylinder, half inch diameter. ROughly the size of a 5 watt cement resistor. ANd heavy - feels like ferrite.

    ANyone have one or recommend a source?

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    Enzo,

    I know one company that could make such an inductor but this is in Europe (Poland): http://www.feryster.pl/polski/dlawiki-cewki.php?lang=en
    They can make everything if you provide documentation or parameters of the inductor (or original inductor). But of course it may be to expensive to manufacture the inductor in Europe and send to the States . I'm sure that similar companies exist in the States (possibly in your area).

    Marek

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    Senior Member Enzo's Avatar
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    Thanks, that might work, but even domestically, it would be cost prohibitive, I fear.

    SInce it is an LC circuit, I was thinking of possibly changing to a larger cap and smaller inductor. 2.5Hy is hard to find in such a small form.

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    Noodle of Reality Steve Conner's Avatar
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    Hi Enzo

    Transformers are just inductors with extra windings, so it might be worth trying whatever audio transformers you have lying around. For instance a 600 to 10k mic matching transformer, if the 600 ohm winding doesn't give a resonant frequency in the ballpark, the 10k might.

    The only problem I could think of is if the signal level at 100Hz were high enough to saturate a mic transformer, then you'd need something like a 10k to 10k transformer from a line isolating box, which are rated to take line levels. Or maybe an audio transformer from an old transistor radio. (I shouldn't remember such things at my age ;-)
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    I was curious and I called them to ask for price. I was not able to provide any technical details so I got very rough quotation: between 10 and 30$. Can you post a photo of this inductor (and dimensions)?
    Of course time would be an additional cost .

    Marek

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    Quote Originally Posted by Steve Conner View Post
    Hi Enzo

    Transformers are just inductors with extra windings, so it might be worth trying whatever audio transformers you have lying around. For instance a 600 to 10k mic matching transformer, if the 600 ohm winding doesn't give a resonant frequency in the ballpark, the 10k might.

    The only problem I could think of is if the signal level at 100Hz were high enough to saturate a mic transformer, then you'd need something like a 10k to 10k transformer from a line isolating box, which are rated to take line levels. Or maybe an audio transformer from an old transistor radio. (I shouldn't remember such things at my age ;-)
    yeah you might try those little ones(which I guess are meant for use with transistors). Have some data for some Hashimoto/Sansui(similar types are sold at Mouser and I would think more variety may be avail. surplus) :

    ST-71: 600 ohms (51ohmsDCR) to 1k (83ohms). The 600 ohms side is about 700mH, so possibly get a 600 to 600 (some in Mouser cat. with bit higher DCR), then wire in series (700mHx4=2.8H). (1k side about 1.2H.)

    ST-23: 2k (300ohmsDCR) to 2k(170ohmsDCR). About 3.3H ea. side. (So maybe something a bit less using one side.)

    ST-73: 1k (84ohmsDCR, 1.2H) to 1kCT (83ohmsDCR, 1.2H). From one side full to other side CT is about 2.8H.

    Mouser has:

    shielded audio transformers

    429-7209 500CT (40ohmsDCR) to 500CT (38ohms DCR)
    429-7216 600CT (65ohmsDCR) to 600CT (55ohms DCR)

    plus a bunch of "HiQ" audio transformers

    p.s.

    also, mesa/boogie uses inductors for EQ in some amps, so possibly you could find something close and get one from them?

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    Senior Member Enzo's Avatar
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    Got no photos, maybe I ask for camera for Xmas next.

    I mentioned this is a small part, about 1" long and 1/2" in diameter. 24mmx12mm dia.

    My concern is finding a part that makes sense in terms of fit. This is not much larger than a 5 watt cement resistor. It is on an eyelet board in a row of other similar inductors as well as more common resistors and caps.

    Here is a poor scan, the circuit is the 5 band EQ lower left area.

    http://www.schematicheaven.com/fende...180w_schem.pdf

    I am not sure there is room for a lot of transformers under there. The innards of this amp are pretty stuffed.

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    the ones I'm referring to are pretty small. Maybe slightly bigger than a sugarcube, so possibly one will fit?

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    Senior Member Enzo's Avatar
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    Oh, that is small. I'll look into that.

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    they are about this size (see pic--sry not the greatest pic but hopefully you get the idea).

    also, there seem to be others avail. (besides the ones from Mouser). For example:

    http://www.oselectronics.com/ose_p119.htm
    Attached Thumbnails Attached Thumbnails transistor-transformers.jpg  

  11. #11
    Senior Member Enzo's Avatar
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    Cool

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