50 watt Marshall Super lead problem

[Firestorm]

60Hz is also the sound you hear (in the US) when you plug a cable into an amp and touch the tip with your finger. Kind of hard to tell the difference between 60 and 120 (at least for me).

[selloutrr]

Being that 60hz is doubled to make 120hz they share. If you tame 60 it will also change the way you hear 120hz. A lot of times when mixing you may want to turn down a freq but not take away it's presence so you cut the lower multiple to thin out the high freq energy.

60. 120. 240. 480. 560. 1120. 2240. 4480. 8960. Etc

some freq round on a 1/3 graphic but you
get the idea.

120hz is still ground related possibly the power line service ie floresent lights dishwasher etc.

[Firestorm]

Yeah. The real problem is when the 120Hz hum is able to modulate the signal itself (usually because of inadequate filtering). Then you get a whole menagerie of sum and difference frequencies that typically sound awful. But they only happen (when it's a filtering problem) when you really push the amp; at low power, it sounds fine. I don't know if typical 60Hz hum has enough amplitude to do quite the same thing.