There is no reason for the send level to be at any level since I am not using it. I normally keep controls that are not in use at lowest possible. However, the send level is derived from the output transformer, makes no difference what it is set too. May have been moved during the rehabilitation of the Mark V. When I got the Mark V combo shell, I could have just swapped the amp into it since it came with a mint MC90. I was not overjoyed with the MC90 and the Mark IV so I did not bother and jumped to the front mount conversion with the EV. If I had gone the T-nut route, I would be able to swap speakers without removing anything except the front grill. I had issues with those in the past so I did not use them in this project.
I spent a few hours ignoring the other amps and focused on the Mark V. I ran both 412 though it at the same time as a full stack and was in Mesa Heaven (reason for being in the center). Later on in the day I focused on just the combo by itself and combo with the extension cab. Before wrapping it up last night, the Roadster was calling for attention. I would definitely get the Roadster as a head and convert the Mark V to a combo any day. During my like or dislike trial of the Mark V I decided to change things with the preamp tubes. The Mullard reissue tubes did a great job in rolling off the high end for driving a 412, but as a combo it was not necessary. Since I had 5 of the Preferred Series 7025, they were installed from V1-V6. V2 is still the vintage Mesa (Chinese) tube. The 7025 are slightly less gain than the Mullard at certain frequencies. Gives me less clip on the clean channel and really wakes up the Mark IV mode in CH3. What I really like, all I had to remove was the back panel, with the amp on its side, I was able to get to the preamp tubes with ease. I still had to remove three of the power tubes to get my hands in there but not a problem since I did that anyways. Took me less time to remove the shields, swap a tube and install the shields. Normally as a head, I would spend more time trying to get the shields back on due to lack of space (main reason why I used to pull the chassis out, plus you do not need to wait for the power tubes to cool down to do a complete tube roll. I will still do that for tuning purposes if needed. Removing the chassis and installing it is a bit different in Combo form. ) Case with the Roadster, I can access the V1 tube easily. The extra long shield is a bonus in that amp, it was a curse in the Mark V. I have removed the chassis of the Roadster just to see what was inside. Quite a simple layout compared to the Mark V. The RA100 has more complexity to it too. For ease of tube replacement, the Roadster wins. The RA100 is easy but there are many parts that have to be removed from the back to gain access to the tube section. The Roadster is quite similar to the Mark V in terms of cascaded preamp tubes. However what is a bonus, the Roadster does not split the reverb circuit between two tubes and share the other half with a gain stage like it does with the Mark V and the Mark IV. It is similar to the RA100, one tube for send/return, one tube for effects send/return. 3 first tubes are the gain stack for all channels, RA100 uses first two as the gain stack for the Hi/Lo gain channel, and 4th and 5th for the clean channel.
Either way you go when the time comes, the Roadster or Road King would be an awesome addition to your arsenal. The Mark V is a great amp too. I wish it was a Dual Rectifier like the Roadster, Rectifier tracking at 100W is nice 8) , with the Mark V you get stuck with diodes at 90W, that is not a bad thing, however CH2 would benefit in crunch mode with tube rectifier tracking at 90W. There is so much to explore with these amplifiers. As for tube rolling, the Mark V can easily be altered with different tubes which tends to be perplexing at best. The Mark IV and Roadster do not seem to be altered much with different preamp tubes (at least it is not as dramatic as it is with the Mark V). The RA100, that is a different story.