[BrendaAnnD]

The most likely circumstance is that you have high power stations in line of sight, and very closeby (3 to 4 miles, or closer). This allows the front end to overload, and creates a lot of intermodulation products. Combine that with a local oscillator that does not generate a perfect sine wave.

I don't know whether Philco uses low or high LO on their prewar FM sets, but especially if the LO is on the low side of the incoming frequency, say, 42 - 9 = 33 MHz. Tripling this (3rd harmonic is the strongest harmonic) gives you 99 MHz. 99 + 8(x3, remember you're tripling) = 123 MHz. So, you have a LO product of 99-123 MHz. Now subtract your 9 MHz IF from this, you get high side mixing product of 90 - 114 MHz. This does give you a possibility of receiving strong stations over most of the modern FM band, plus a bit of the aviation band.

Now, the math works out a bit different if they're using high side mixing to start with. 42 + 9 = 51. Double this gives you 102 MHz. This results in a LO range of 102 + 8(x2.. you're doubling here) = 118 so 102-118. Now, subtract your IF (102-9= 93) so your range then becomes 93 to 109 MHz. Still most of the band.

And all of this is possible because of high power stations and dirty local oscillators. At VHF frequencies, it takes a lot more effort to make a perfect sine wave.

Isn't math fun?