Want to make small inductor for tone circuit - diyAudio
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Old 7th January 2013, 02:33 AM   #1
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Default Want to make small inductor for tone circuit

My Fender Super Twin has normal tone controls, then has a rotary graphic section. One band is out due to an intermittent inductor.

The first section is labelled 'presence' and only has bost, not cut.
.033 mfd 200 v cap in series with an unknown inductor.

2300 HZ band: .047 mfd 200 v cap in series with an unknown inductor.

1250 HZ band: .082 mfd 200 v cap in series with an unknown inductor.

485 HZ band: .22 mfd 200 v cap in series with an unknown inductor.

235 HZ band: .47 mfd 200 v cap in series with an unknown inductor.

100 HZ band: 1.0 mfd 200 v cap in series with an unknown inductor.

Enzo posted on another forum with the same situation but on the 100 HZ band:
EQ inductor for old Fender

He determined:
"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."

So mine was he next band over; the capacitor about doubles for each octave band; I would imagine the inductor should also. So he has 1.0 mfd and 2.5 henry for 100 HZ; I'm going to guess mine (with .47 mfd) is 1.25 Henry.

Those are still pretty large values, so for such a physically small inductor it's probably quite a bit of thin wire.

I suspect physical or thermal-cycle physical damage, not electrical burnout.

I've got some questions:

1) What's the easiest way for me to make some kind of bridge circuit to measure my intermittent inductor when it's working? I have a VTVM, a signal generator.

2) Any good ideas where to purchase a nice core and wire to wind my own, or an approproate commercial product.

I guess I could certainly find some core with insulated leads, wind thin wire on, and test with pink noise and the running circuit, watch the knob's effect on a RTA and get it close enough for a guitar amps.
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Old 7th January 2013, 03:00 AM   #2
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To get up to 2.5 Henries it almost certainly has an iron or ferrite core. Even easier than a bridge is to resonate it with a known film or mica capacitor and look for the peak or dip with the vtvm. Calc the value from the frequency and cap value.
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Old 7th January 2013, 03:54 AM   #3
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That 1.25 Henry value from Enzo's post is pretty high, but these are high voltage tube circuits...
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Old 7th January 2013, 06:16 AM   #4
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Quote:
Originally Posted by cyclecamper View Post
My Fender Super Twin has normal tone controls, then has a rotary graphic section. One band is out due to an intermittent inductor.
Can you post pics, color code, or part number? I think have most of a set from a Super Twin Reverb just kicking around in my parts stash, maybe even all of them.

Last edited by Passinwind; 7th January 2013 at 06:23 AM.
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Old 7th January 2013, 09:25 AM   #5
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Quote:
Originally Posted by Passinwind View Post
Can you post pics, color code, or part number? I think have most of a set from a Super Twin Reverb just kicking around in my parts stash, maybe even all of them.
Oh man, if you actually have the real thing that would be incredible! It looks like a capacitor but is heavier and the body is black ferrite and the ends are sealed with epoxy where the leads come out. The only markings are the Fender part numbers. The one I need is marked 011945 in white print.
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Old 7th January 2013, 09:30 AM   #6
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The Fender inductor part numbers are:
011941 (preesence)
011942 (2300 HZ)
011943 (1250 HZ)
011944 (485 HZ)
011945 (235 HZ)
011946 (100 HZ)
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Old 7th January 2013, 09:33 AM   #7
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It's about an inch long, bit less than 1/2 inch diameter tube.

It seems the wire is probably very fine, to achieve that value in such a small package. The leads come loose, and break the wire. So I might put an extra dab of cleaner and epoxy on each, just to help prolong their life.
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Old 7th January 2013, 09:33 AM   #8
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What would you like in trade?
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Old 7th January 2013, 06:20 PM   #9
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Quote:
Originally Posted by cyclecamper View Post
The Fender inductor part numbers are:
011941 (preesence)
011942 (2300 HZ)
011943 (1250 HZ)
011944 (485 HZ)
011945 (235 HZ)
011946 (100 HZ)
Yep, I have one labeled 011944 and the rest just have color coding dots painted on. PM me your address and I'll ship you the whole set. Some kind of trade would be fine, or you can just pay shipping.
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Old 7th January 2013, 06:44 PM   #10
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That's really great! Will PM now! I wonder which is which, but I should be able to put them in order at the least. I wish they'd put the real values in the schematic too!
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