Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Sonny ReVerb on March 22, 2023, 04:11:51 pm
-
I'm going to attempt to wind an inductor for a Selmer type amp, since I've never found an off the shelf part that is close. This is the 9.5H inductor used in the tone circuit. It's a bit daunting getting started and I have no idea what I'm doing, but if we can design something suitable I'm sure it would help others wandering down this rabbit hole. Anyone have any experience with DIY inductors? Any and all help appreciated!
Suppose a ferrite bobbin core with a one inch diameter and relative permeability of 200. Any links to a suitable core greatly appreciated.
The inductor doesn't need to pass much current, so I would think smallish wire should suffice. I have some 42 AWG magnet wire for winding pickups. Would that be adequate?
Starting ballpark numbers would give an inductance of 9.52H [handy calculator (https://rimstar.org/science_electronics_projects/coil_design_inductance.htm)]:
Relative Permeability - 200
Number of Turns - 5300
Core Radius - 0.5"
Wire Diameter - 0.0028"
The original is in a can that looks about 1 1/2" or so in diameter.
-
I do not know if this is helpful at all, but... I built up the earliest version of the Gibson EH-185 a while back. It had an inductor in the tone circuit. PRR and others helped me find an appropriate inductor. They also warned me that inductors in the tone circuit could be hum machines. But I wanted to build it stock first, which I did, and then changed the tone circuit to something more common.
I'm thinking you might be able to find an appropriate inductor. 10H chokes are common. There are none that are close enough?
-
> Number of Turns - 5300
> Core Radius - 0.5"
So probably 3,000 Ohms dead resistance? Might be enough to swamp the EQ action. Hard saying, not knowing the schematic.
The Hammond 125ESE transformer is near 10H, and good low resistance, but far far bigger than that can. Look to Hammond's choke list and find a comparable. In fact, find a 10H-12H choke, buy it, then de-wind to your specific inductance. Even buying retail, you won't get right-size iron and copper any cheaper than a stock part.
-
Ok, I ordered a Hammond 157H 10H 50mA 408 Ohm choke. Y'all are harshing my DIY buzz ;)