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Classic symptom of 3.58 oscillator drifting, you get rainbow bars. Phil is intimately aware of this problem.
There can be 3 reasons why this happens:
1. the crystal is going out, and the reactance tube can't pull it in to lock solid
2. a problem with the oscillator circuit itself (try twiddling the frequency coil near the tube)
3. alignment is so far off that the 3.58 information contained in the signal is too weak for the set to lock on to
Of course check the tubes, but you'll likely find a bad crystal or the oscillator coil out of whack. When you tweak the coil, you have to ground the signal coming from the phase detector or it'll just wander all over the place. You should see the rainbow bars float by slower and slower then they will lock in. Right before it locks, you'll notice the number of bars is getting smaller and smaller as the frequency gets closer and closer to being right.
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