Pultec Inductors again...

[Core]

The bandwidth pot on a Pultec is 2K5, so 10% of this value (the tolerence of
the original AB pot) is 250 ohms, so, even a 20% disparity DCR on the
inductor would only be about 6 ohms at the highest DCR value.
The DCR is only important when verifying that an inductor was correctly
reverse engineered, because it's one parameter (of many) that could indicate
when an inductor has been wound differently than the one you're trying to
copy. A wrong DCR reading can indicate other parameters (that affect the
sound of the inductor) are different than the inductor that you're trying to
copy.
The lower or higher inductance just requires a cap value adjustment. One which
you'll need anyways, as your inductance values don't look like Pultec values
anyway.
If you're trying to make a copy of a Pultec inductor, the DCR, as a
clue, could be more important than the inductance.

 

[Core]

Measure L and DCR of the individual taps, and wrap the actual inductor
100 times to get a reference value of the completed inductor. The popsicle stick
won't work on this small of an inductor, it's too wide to get you to the final
windings.
As far as the length is concerned... #34 wire is 3.8329 feet per ohm.
Shoot for about 30.9 ohms at the longest tap, so, through simple
multiplication figure that you would need about 118 feet... round that up
to 130 feet. So, 70 feet isn't going to get you very far at that target DCR. A
1/4lb. spool will get you close to 2,100 feet.
#34 wire is 8310.8 feet per pound

 

[Core]

The original Pultec inductor

The core is black.
The dimensions are as follows:
Outside diameter: 23mm
Inside Diameter: 14mm
Height: 8mm
AL value of the core is 876μH. Test this by wrapping 100 turns around your core, then measure the
inductance.
The wire gauge is #34AWG
Calculated turns are as follows:
32.2mH 606 turns
50.9mH add 156 extra turns
84.1mH add 218 extra turns
98mH add 78 extra turns
147.5mH add 240 extra turns
Turns formula:
N=100 x SQR(L/AL)

Where:
L= desired inductance in μH
AL= AL value in μH
So, for the 32.2mH tap...
N= 100 x SQR(32200/876)
N= 100 x SQR(36.75799)
N= 100 x 6.06284
N= 606.284 turns

 

[Core]

The original inductor measured approximately (with wire):
OD = 23mm
ID = 7mm
Height = 8mm

The core used miced out at:
OD = 22.9mm
ID = 14mm
Height = 7.62mm
obviously not the same size as the original raw core, but it worked out.
There is no possible way to get 1000 turns around the original inductor, so
use the "standard" way of determining the AL value of a iron powder core,
which is 100 turns. The 1000 turn standard is a more modern
one, that was used as cores got better, maybe to make the math much easier.
At the current, 1000 turn standard, figure an equivalent AL value of 90

 

[Core]

The ORIGINAL Pultec inductor is bare, without any epoxy.


23mm - 7mm = 16mm
16mm / 2 = 8mm
multiply that by the height and you get 64 sq. mm or 0.64 sq. cm

That puts a permalloy core a bit over the top when hit w/ a
22dBu 3K signal, which is really hot for a Pultec at 12 on the HF boost control.

 

[Core]

Hope this helps the people. All information necessary to DIY a Pultec inductor as in the original EQP 1-A and EQP1a and EQP-1-a
later model inductor for sound exact like original.

Work good for me but I don't know how these work for you !!!!!

 

[damiangiannis]

Does the same formula applies for meq-5 inductors ?

 

[CJ]

yes