So I am going to switch out the pre-amp tubes. I did this before with a DSL and enjoyed using JJs and Tung Sol instead. I never changed the Power Tubes though for the DSL. I am going to replace the stock pre-amp tubes with 2 x TAD 12AX7/JJ ECC83s and 1 x Tung Sol 12AX7. I am thinking of using the TAD/JJs for V1 and V2 and the Tung Sol for phase inverter in V3. After that, I will consider if I want to replace the power tubes or not. I have done this before on other amps that needed to be biased again and have dug out schematics and done this myself with a voltameter and turning the bias pot. I am extra careful. I suspect however that with the Origin 50 the stock power tubes should be okay. If not I am thinking of getting a matched set of TAD/JJ EL34 and then bias manually. A bit more expensive to do so I will hold back unless I really think I need to do this. If I do that how many mV across test point CN32? Test point appears under the yellow wire and Trim 1 pot is the black round pot on the top left portion of that picture. Any advice or special tips, welcome.