I bought these recently on TradeMe for $15. The brand is Tokumi and I had never heard of it but It turns out that they still manufacture headphones (somewhere in SE Asia). They have a 2ch / 4 ch switch on each side, and the seller mentioned that switching didn't seem to make any difference. When I got them it was obvious what the reason was - there was only one plug. Once the Quad thing had died someone must have decide that they were worth converting to stereo by wiring the front and rear drivers in parallel. I tried them out wired like this and they actually sounded quite good - spacious, but lacking treble. The mids are slightly honky, but I don't think damping the drivers was considered back in the early 70s. Back in the days, I was quite keen on Quad and experimented with several QS and SQ systems, as well as discrete 4 ch (on a Sony Quad tape machine, I never had a CD-4 system).