IF stages
Seeing as it's very hard to find 10.7MHz IF transformers for tube radios, I've decided to wind the inductors myself, because I want everyone around the world to be able to recreate this.
The result is shown on the right. The coils are simply wound tightly on a plastic pen. This allows me to adjust the spacing between them, affecting the frequency response curve. This is vital for all IF transformers. If they're not properly spaced, AM modulation will be introduced in the IF stages, and we don't want that! The base is a small piece of plexiglass which it is glued into. I may need to add a casing later to prevent it from inducing the IF signal in other parts of the circuit.
I've already tested this setup in a working tube radio, and it does indeed work fine. However, there are three other IF stages in that receiver, so I can't verify a proper frequency response. I will test these transformers at my local university, where they have the equipment for testing frequency response.
Final stage
Working backwards, I have just finished routing the PCB for the last IF stage (the one before the demodulator). Here it is:
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