Hey folks, A few years ago, I picked up a '78 Bassman 70, SF obviously. I was looking for alot of headroom and a good base tube tone to build from with pedals. For this, the amp has been great. I got it for under $300 and it's in mint shape. Lately, both my skills and my ear are surpassing what I am getting back from this amp. Naturally, I am considering an overall upgrade. However, I will keep it in the Bassman family and get an AB165 BF next. Before that though, I wanted to do some real homework on the 70 to see what I had to work with. I will probably never sell it and will just experiment on it. I am a Mechanical Engineer with some fundamental electronics wherewithal. Before I go tearing apart an AB165, I would like to have some experience here. So, as I begin my research I have some questions. There have been a few good threads on the Bassman and lots of web resources; however, i still have questions: Circuit Identification: From my research at FFG that the amp is one of these - AB165, AA568, AA270, AA371. I am assuming that it's not a 165. I am guessing likely a 371. I cannot find any info on the amp or the tube chart to suggest what it is. Is the best way to open and compare circuits to schematics? Are there any other indicators I should be looking for? Discharge: Is there a "best practice" for draining off caps so I don't blow myself up? I can tell that this amp has been serviced and I want to see to what levels by opening it up. Tubes: The tube chart reads (2) 6L6 GC Power Tubes, a (1) 12 AT7 phase inverter and (3) 7025 pre-amp tubes. However, it has (2) Svetlana 6L6 GC Power Tubes, a 12 AX7A (Made in China) phase inverter, a GT-12AX7 next to the phase inverter and then the last 2 are GT-7025. Can you tell me what this combination was intended for by the previous owner? Channels 1&2: On this amp, I believe I read that the 2 channels for both the Bass and Normal side have different gain structures. I am assuming this to be true and that #2 is less gain. Jumpers: Before I fry anything, I understand to jumper the # 2 Channels and that provides an ability to bleed in the Bass side using the Channel Volumes and at a lower gain and EQ point. Should I try this? Mods: Without completely Blackfacing the amp, there are some suggested mods, such as: http://www.tone-lizard.com/Bassman_Modifications.htm. I am curious if these are even worth applying. I suspect that an adjustable bias would be the place to start. Thanks for entertaining questions from a newbie. Again if the amp simply isn't worth it, I won't even bother. However, I can find more flexibility and opportunities to improve performance, I wll. I also hope to find some BF Bassmans this weekend to try out. Thanks in advance for any comments!