Is it safe to hit the VPR switch when standby is on? The thought never crossed my mind untill now, I've done it multiple times and it's never damaged the amp but the popping noise is dis concerning.
here's what i googled for you

"The VPR switch on the TSL amps acts like an internally fixed PPIMV (Post Phase Inverter Master Volume) when engaged. This limits the grid drive to the power valves, which allows you to drive the phase inverter harder without the high volume. With this switch, you get more phase inverter overdrive, while the power valves run the same as they do normally, just with a limited grid drive signal."

so hit it as much as you want.
Prs se Holcomb is the answer