Use preamp section only -of integrated tube amp

I have a decent set-up and I am looking for a little advice. I have a Rogue 66 Magnum pre with no phono. The Rogue feeds a pair of Michaelson Audio tube monos into Vandy 2CE's. I have a 1960 Stromberg Carlson Integrated amp (12 watts/channel) that I have rebuilt and which sounds great for my second system. I have recently used the Stromberg integrated for a phono preamp by using the tape out into the Rogue aux input. It sounds great. My question is: Is there a way to bypass the output section of the integrated so I don't use up the output tubes/or have the output transformers powered up while using just the pre-amp section? Also, there is an AF Amp section (6AV6 tube)following the pre-amp section on the schematic. What is an AF amp? thanks in advance, Ralph
From what I've been told, the tape out usually bypasses all tubes? You should compare the SC to an inexpensive phono pre and see if it makes a difference.