I am starting to build a Tweed Pro with a 15 inch speaker for a friend of mine and I am still a little undecided which version to base it upon. My friend leans towards the 5E5 (First he wanted a 5E3 but he has these great sounding NOS 5881 Tungsol tubes, also he heard that Keith Richards just bought one plus he probably does not really need the additional power of the later version...) I'm a bit uncertain which version would best suit him. Here are my thoughts so far: Input section: I am inclined to use the input of the 5E5-A with only one 12AY7 (the same as the 5E3 Deluxe) since the 5E5 seems to "waste" whole 12AY7 by using one tube for each channel. Or am I missing something here? Does the 5E5 input version bring something to the table the other one has not? Tone stack: Anybody has with experience with both tone circuits? Again I lean twoards the simpler 5E5 tonestack (one pot tonestack, volume pots, mixing resistors), on the other hand the 5A5-A (molume pots, mixing resistors, two gainstages, two tone pots) has two additional gainstages and might be more versatile. I could probably use the simpler tonestack an still add another gainstage. Hm...or maybe add a tremolo circuit with the "leftover" tube? Or a one tube reverb? Power supply: I am thinking 5e5 values and maybe add the choke of the 5E5-A better filtering (maybe upping the first cap to 33mf?) Bias circuit: I might install a cathode/fixed bias switch or just use cathode bias NFB Poti or switch: I like this option in all of my amps, you can have both amp versions, off for 5E5 and on for 5E5-A, or anything in between. So basically right now I would build a 5E5 plus adjustable feedback loop and bias switch. Other things I might add: 470 Ohm Power tube screens resistors, elevated heater voltage... I would love to get you input on this. Thanks!