Beware that different types of 6L6 tubes have different operating level ratings and recommendations. But never set the bias current so high as to exceed the plate dissipation limit set by the tube manufacturer at any portion of the tubes operation. The higher you set your bias, the hotter your tubes will run and the earlier your sound will break up. When you adjust the bias on your amp you are adjusting the level of current available to the power tubes. Setting the bias on your amp is like setting the idle on your car. Without a good working knowledge of electronics you could blow your amp, or your tubes, and possibly kill yourself in the process. Unless you know what you are doing, never attempt to adjust the bias on your amp yourself. When you replace the power tubes on a Fender Hot Rod you should always have the bias setting adjusted to ensure that your tubes are operating within safe limits and you’re getting the kind of tone that you want from your amp. But thankfully help is available in the form of an old article by Justin Holton at The Unofficial Fender Hot Rod Deluxe Owner’s Guide. I did a lot of research before deciding to replace the Hot Rod’s factory-fitted Groove Tubes GT-6L6 C(HP) power tubes with a pair of Ruby 6L6s and learned much about 6L6 variants and their different power requirements along the way. What I want to discuss here is the bias setting for the power stage in a Fender Hot Rod Deluxe. I gave a full review of the Ruby tubes in an earlier blog post. I recently fitted the power stage of my Fender Hot Rod Deluxe with a pair of Ruby 6L6GCMSTR tubes.

Variable bias vs fixed bias guitar amp