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The hum is a definite AC hum, the same frequency as the clock motor. Even though it's a Japanese radio, it has a GE Telechron clock which are known to get noisy over time. The caps were replaced with exact values save one: a 30mfd replaced with 33mfd. All tubes test good, two originals were replaced with my own stock. Hum is not band specific, heard in both am and fm. I could try shielding the 12BA6 or 12BE6, but I'm skeptical anything will change unless the radio is simply a bad design. I'm still doing tests so keep the suggestions coming.....
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