Hi everyone
Just a quick update and a question :
I finished rebuilding the preamp from the ground up. I went with the FixThatMix schematics, but used the PSU we designed here, as well as a 5879 preamp tube from the Ampex 600 design. The input and output transformers are Altec 15095a, wired 150 > 15K for the input and 15K > 600 for the output. I don't have a 12AY7 in my stash so I replaced with a 12AU7 for now.
I have a huge amount of gain, but microphonic tubes and I think I miss some low end extension going straight into my AD converters.
I tried with a 15K : 15K Altec output transformer, it's better, yet it's not perfect. I could be tempted to blame it on the input transformer, but I have the same sensation when using the DI input with my P bass.
Where should I look ? I don't think the 12AU7 instead of 12AY7 could be guilty...
I am considering finding a better input transformer than the Altec 15095a (by better, I mean a dedicated mic input transformer with maybe a 250 primary to match my RCA Varacoustic)
Thanks for reading, and thanks all for your help