Selectosphere

[pwdrive]

Not trying to sound vulgar but after looking at the selectosphere I now know where men can get a certain affliction from (me included). A good job that it didn't catch on I suspect.

Yes, it's a strange looking thing, as far as I can see it was designed to be an aid for single signal reception in relation to TRF receivers, not that far fetched, as many headphones were designed with a resonant audio peak to aid in CW reception.
You could argue that it was more efficient than a conventional audio filter system given the insertion loss that an audio filter would represent.

National made the Selectoject, not sure if that was audio based or Q multiplier, will have to check.

Lawrence.