Fender Studio Bass Amp (EQ inductors?)

[manolo]

Hello !
The problem is that the 1850 Hz pot and the 390Hz pot from the EQ section wont do anything because the two inductors-coils are open circuit .
The coil from 1850Hz is marked as 011942 BRN-BLK-BRN and
the coil from 390Hz is 011945 BRN-BLK-RD
image shows coils with one leg unsoldered

The question is what replacments to look for?
Thanks for any help!

[Jazz P Bass]

Try this calculator: http://www.electronics2000.co.uk/cal...calculator.php

BRW-BLK-BRW = 100 uH

BRW-BLK-RD= 1 milliH

[MarkusBass]

I'm afraid that this is not exactly what you need. It's because the inductors for such equaliser should be in range 0.1 to 2 Henries. This is from 100 mH to 2000 mH. The formulae for LC circuit resonance frequency is given here: LC circuit - Wikipedia, the free encyclopedia . Do the calculations and I'm sure you get results in range of one to several Henries.
My guess is that:
RD-GRN-RD is 2500 mH = 2.5 H (80Hz)
BRN-BLK-RD is 1000 mH = 1H (190 Hz)
390 Hz - also 1H (with different capacitor)
RD-BLK-BRN is 200 mH = 0.2 H (1000 Hz)
BRN-BLK-BRN is 100 mH = 0.1 H (1850 Hz)
GRN-BLK-BLK is 50 mH = 0.05 H (PRESENCE)

With these inductors it is also important to know the DC resistance of the inductor. It's because this influence the Q factor of the filter. So inductors with different DC resistance may cause the amp sound different.

Mark

[loudthud]

MarkusBass corrected his post.

[MarkusBass]

2000mH is 2H !!!

Did I make a mistake? In which line? Please correct me if I'm wrong.

[MarkusBass]

I changed the first statement and added the list of inductors. Maybe there was somewhere one "0" missing for a moment (I saved the post in between). Sorry.

[g1]

I think he was just making a statement that 2000mH = 2H.
His disagreement is with the values given by the color code calculator for this particular circuit.
It would seem the multiplyer is off or has not been given by the OP.

From another forum:
"Don't think it's a typo after running some quick online calcs to solve for simple LC resonance frequencies. Here are the actual inductor values, as best as I can figure:

011941: 50mH
011942: 100mH
011943: 200mH
011944: 500mH
011945: 1H
011946: 2.5H"

[nashvillebill]

I have a Peavey Series 400 bass amp from the early 70's which uses inductors on their 6 tone controls similar to the Fender design. Inductor values and caps, hi to low frequencies, are:
25mH--0.03uF
100mH--0.05uF
200mH--0.01uF
400mH--0.22uF
800mH--0.47uF
1.5H--2uF

There's also a 470 ohm resistor in series with the L and C.

[g1]

My wild guess is that the supplier of these inductors "invented" their own color code which gave the value in milli-henries rather than the proper micro-henries. Then whoever drew the schematic just went by the colors on the actual inductors rather than specifying the actual value (which may have brought some attention to the error).
I think if manolo measured them with an inductance meter he would find they are in agreement with the values given by markusbass.