[etech]

The better selectivity on the Model 90 is due to the lower I.F. freq of 175 kHz., as opposed to the 460 kHz. on the 650.

Yes, I hadn't thought about that, Chuck. But , if all other factors were equal, than the 175kc I.F. ought to be a little better than 2.5 times more narrow.

Also consider the fact that the Model 90 has Philco's "double tuned input curcuit"; i.e. two tuned circuits ahead of the RF amplifier tube, which is designed to provide sharper selectivity.

Ron, yes I am still very impressed by this fact. That four gang tuner with the double tuned antenna coil was quite an advanced circuit for its day. Philco spared no expense on that.

I have to say that I'm still very surprised by the performance of the model 90. I guess the use of those #24 screen grid tubes made quite a difference. After all, it is quite advanced for a 1932 set.

Ed