Could well be the couprit.RectifiedAmps wrote: ↑Fri Jan 29, 2021 12:09 pm This is a bias-wiggle tremolo right? To me it sounds like the bias is set too cold on the output tubes, so when a strong tremolo LFO hits them, they’re getting pushed down into even lower bias, causing crossover distortion. This type of trem works great on cold-biased amps, but the effect can be TOO strong, which might be what you’re experiencing. If you’re comfortable with it, try running the bias a bit hotter and see if the fizz disappears.
Starting to get a bit beyond my level of amp tweakery tho.