Pedro,
I want to give you a slightly different approach to look at. Please click on this link and notice the modification that Gary W3AM made to his Viking Ranger. It is taken from the Ranger modifications originally documented by Tim WA1HLR.
http://www.w3am.com/ranger.htmlIn this change, the driver transformer is eliminated entirely. I have found that most of the limitations in both the Ranger and the Valiant center around this transformer. The phase inverter circuit, suggested in the diagram shown on this page, has worked very well for me. It eliminates the fidelity restrictions imposed by the orginal driver transformer.
It is so simple and requires but a very few inexpensive parts. In both my Ranger and in my Valiant I use this same circuit, one half of the 12AU7 as a phase inverter and the first half as a voltage amplifier, preceeding the phase inverter. I feed line level audio into a UTC A-11 transformer, which matches the balanced line level audio from my audio equipment into the grid of the first half of the 12AU7. I also mix audio from the microphone preamp in at this point. The old clipping coltrol is line input gain and the old audio pot is the microphone gain. You can choose one or both audio sources this way.
If you choose to try this circuit there is one caveat! When you wire in the voltage to the plate of the phase inverter, you must find another source of HV for that tube. In the Valiant, the HV is switched off and on (transmit to receive) and in doing so the coupling caps to the grids have to charge, causing a very heavy mod current spike. I believe that I tied it to the low B+ (380 volts) and that worked fine.
The 6146's are biased to run in AB1 and provide plently of audio for the finals. For a while I removed one of the 6146's from the finals, making it a pair modulating a pair. I was concerned mostly with the heat and the extra loads placed on the transformers by running it where Johnson wanted it run. By removing that tube and solid stating the power supplies, a lot of heat was eliminated.
Later I put the extra 6146 final back in and it's fine that way too but I still only loaded it to about 230 ma. This gave me 105 watts of nicely modulated RF out. I loaded it heavier to test it and still could modulate it well but not with the reserves that gave me good asymetrical positive peaks at the lower power settings. I doubt that anyone that listened to the Valiant could tell that it wasn't running the full 145 watts .. the difference was not important.
The Valiant mod iron suffers from the same characteristics as the Ranger's in that the waveform starts to show funny lumps and bumps below 150 hz. The mod transformer is not the best but it does sound real good and works fine. I generally roll off audio under 200 hz anyway.
This mod has worked very well for me. I used this phase inverter circuit on an Apache also and it also sounded very nice. In this case it was a pair of EL34's instead of 6146's (slight different bias settings) being the only difference. In fact, I use EL34's in my Ranger too but the same phase inverter circuit.
Best wishes on your restoration, no matter which way you choose to do it, I am sure it will sound great!
--Larry W8ER