Switched to a ferrite core on my old radio and the hum vanished

I've been trying to fix this 1960s Grundig tabletop radio for weeks. The hum would never go away no matter what caps I swapped. Finally read a post about wrapping the power cord around a ferrite core. Did that last night with a core from an old monitor cable. Worked way better than I expected. Anyone else find simple noise fixes for tube gear?

2 comments

2 Comments

thead442d ago

That "wrapping the power cord around a ferrite core" tip is a classic. People don't realize how much noise radiates straight off the power line into old tube gear. If the hum's still a little there, try putting another core right near the chassis entrance.

wrenstone1d ago

Yeah I've done that exact thing on a few old Fender amps and a Silvertone console I restored. The difference was night and day, especially with the power cord running right past the input jacks. Something else that helped me was actually moving the core around while the amp was humming to find the sweet spot before I zip tied it down. Usually right where the cord first touches the chassis or where it passes near the power transformer is the worst spot. If you're still getting a low rumble after that, check if the wall outlet is grounded properly too, old houses can have sketchy wiring that adds its own noise.

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