Dear matthew,
The F-4 is not a ‘tube-driven’ avionics package.
Solid state avionics was present in the Phantom II E-series avionics package, which came out in the late 60’s.
You are likely correct, my knowledge on the subject is limited to what I read in the Tom Clancy/ Dan Brown novels. However, I can assure you from personal experience our B-52s and some of the Navy’s ships of the mid/late 60’s did utilize tube type Cryptographic gear.