ferrite core inductor
https://www.openlearning.com/u/lippard-qavutb/blog/10ThingsWeAllHateAboutFerriteCoreCable/
The Emi Main is built up of ED Ef (Emitter Farad) and B+ in the output. Within the enter to the Emi Core the output impedance could be held lower to lower any feed-back issues. The BC235 is Commonly employed to