Just completed a D-958 circa 1956.It has more bells and whistles than one might expect from that vintage AA5.It has a wood cabinet,mahogany finish,phono input,tone control,dual 6 inch speakers,neon power indicator,and 2 speed tuning.Outer tuning knob tunes the complete band in 1/2 revolution and inner tuning takes 3 revolutions end to end. Unusual for no SW bands. Also, output is 35C5 instead of 50C5. A 100 ohm resister is in filament circuit to drop about 15 volts.My guess is the AA6 was discontinued leaving an inventory of 35C5s which they were using up. Any other thoughts on this bit of trivia?
Correction--Model No is D-598.
It's more then likely that someone in the purchasing department got a deal on some 35C5 tubes, which they also would have used in a transformerless AM/FM set, they were also used in inexpensive radio-phonograph consoles in push pull sometimes. I've noticed this with some older Philcos, they will have a multiple code numbers of the same model where they will substitute one tube for another, like a 50L6 for a 50A5. The set you have may have shared it's cabinet and chassis with an AM/FM set, or at least some mechanical parts with an AM/FM set, there isn't really any reason to have vernier tuning on an AA5 at all.
Regards
Arran
Arran-I think you are right.Use of the 35C5 probably related to cost control measures-maybe discounts for large volume purchases to satisfy needs for AM/FM sets in addition to the AA5s. Cost of the additional resistor was probably minimal.Dual speed tuning was probably a sales gimmick-no real need.
You can sub 50C5 with no further correction due to today's higher wall current.