Mr Cheeky Sod Here . . . .
If I only knew . . . .The only complete consoles I have known have NO output transformers that I have found . . . yes, unbalanced, but flat response to 140kHz on the line inputs (allegedly). I have often heard people say that Helios doesn't sound "right" without the output transformer. My modules sound great to me! IF there was an output tx, it was only on a mix,aux or group output, and NOT between each module, like Neve, API, etc. So, I would surmise that it has less of an influence on the sound than other British consoles. Very very few Helioses made it into a broadcast situation. I guess that they didn't meet the BBC's unbelievably stringent specifications. I guess not having loadsa tx's limiting the bandwidth would be percieved as a major flaw anywhere near a transmitter . . . I only know of one - in the United Biscuits Network. Imagine! A biscuit manufacturer who had their own Radio station! They distributed nationwide over a super phone network apparently! Nuts!
I would hazard a guess that if they did have an output transformer, it would be a Sowter of some kind, since apart from the Beyer, they used Sowter iron in the mic input (Sowter 3374 in some modules, 3773 in others-both sound awesome btw)
I will try to establish more accurately what if anything was used, - there are more avenues of enquiry!
Andy P