Backshophoss wrote:The M-2's were able to run on 25hz power,and carry a IRON core in the main transformer for that purpose.
As opposed to what? Actually, modern transformer cores are steel laminates, with the alloys selected for their magnetic properties. There is no other technology at low frequencies.
I'd be surprised if it was vented fumes, I was under the impression those transformers were pretty well sealed. Keeps moisture out, and prevents any venting of explosive gases - the latter issue plagued some older British EMUs back in the early 60's, though rectifier arc backs and a misunderstanding of them contributed.
One you get high enough in frequency, you don't need a core - air core transformers were common in radios years ago, with ferrite slugs to tune the characteristics.