Begining of SE transformer air gap experiments

At your risk. All safety precautions should be followed. Any voltage or current can be dangerous.



After so many failures of winding non air gaped cores for class A single ended circuits due to DC magnetic saturation...


These failures took place across the board from nearly as low levels as those on the Pleiades V6 mic booster amplifier to Pleiades EF183 headphone amplifiers to Pleiades BD139, speaker amplifier.


Yesterday 2 medium size D ferrite core had been bought. They look very promising. The can face each other and their smooth contact points can be separated by paper, thin membrane film etc.


For example an old bobbin has been found. Not known how many turns but inductance without inserting anything to it is 134mH.


Just air     134mH
Inserting one E       330mH
Both Es (closing magnetic circuit)    35H
Both Es with separating paper on one side 15H
Both Es with separating paper on both sides 8.5H
Both Es opaque thin plastic film on both sides 14H?


Nice books say that air gap linearises the magnetic circuit.
Changes the H B slope to a gentler one.
The magnetic circuit can be thought of as an analogous electric circuit, the air gap being a much larger rssitor in series.
So it may be thought as a constant magnetic flux current source?


It should be fun adjusting air gap while carefully listening (ear protection measures required).


Inserting the Es would being bass. But if they touch (on DC Singke Ended class A applications) bass may be reduced due to magnetic saturation.


So the right air gap could be found that gives the bass bass and overall sound.


At the moment 2 more windings will be wound on said bobbin. One for a transistor collector circuit. One for 4Ω, or taps for other speaker impedance driving. The already existing winding will be for electron tubes. The medium winding may be also used for driving high Z headphones (attention to hearing damage by high sound presure levels, only very low power devices should be used and all safety precautions taken).


Another way of introducing an air gap? See next post:
https://euroelectron.blogspot.com/2019/06/other-ways-of-introducing-air-gap-to.html


Some nice books:


Engineering Electromagnetics - Hayt
Applied Electromagnetics - Plonus
Electronic Transformers and Circuits (vintage editions too) - Reuben Lee - Wiley
Electromagnetism - Grant, Phillips
Electricity and Magnetism - Purcell - Berkeley
The Feynman Lectures on Physics - Vol II
A treatise on Electricity and Magnetism - Maxwell - Dover
Magnetic Ciruits and Transformers - EE Staff MIT
Radio Engineering - Terman
Applied Electronics - Gray - MIT
Communication Engineering - Everitt