Great clear video! Having a load connected to a speaker or as shown (Suhr reactive load) is shown but I just want to emphasize it. Volumes all the way down. Before pulling the chassis, disconnecting power and turning the amp on with nothing connected to discharge the high voltage filter caps while handling the chassis. As this MODERN amp will do it relatively quickly. For more classic amps, something like Stew Macs’ Discharge stick to drain the caps if anyone is doing any other work inside besides biasing. Showing the biasing itself would be a good follow up video as well to show the balancing between the bias of each power tube and getting them as close to each other as possible. Cheers and safety first, watch those necklaces too!
Without knowing the plate voltage, you're biasing blind and could end up with issues. You really should calculate the plate dissipation. That will give you more consistent results from set to set and ensure they are running within spec.
So, how do you do it? Yes, safety is important but how to and what to achieve is missing. What's the starting point and what's the ending point? How do I know if I have correctly bias it?
Thank you for this very helpful video sir, did you have your amp on standby or turn on? Also did you do this process to both tubes or just one? Thanks.
Another good safety tip is to only use one hand to "cross" the plane of the chassis when powered up (i.e. adjusting the bias pot). The metal chassis is a near perfect ground and if your other hand is touching it, the current will flow up one arm, through your chest, and down through your other arm to the ground chassis. Bad news! A good practise is to put one hand in your empty pocket. Also wear rubber gloves and a long sleeve shirt or a sleeve over your arm to prevent from touching the metal chassis.
I was wondering why there is only one screw to set the bias for all the power tubes. I believe the answer is that when replacing power tubes you’d replace all at the same time with a matched set.
