Changing Preamp Tubes to Lower Gain in a Model T

[jdfarrell81]

Both of my Model T's have 12ax7 preamp tubes, and that suits me just fine when I'm playing guitar through them, but the tone is a bit too aggressive for my tastes when I'm playing bass. I'm thinking about swapping out the current preamp tubes with tubes that will let me get a smoother, cleaner tone and crank the volume a bit more.

Any thoughts or suggestions?

Also, am I correct in thinking that there's no need to rebias preamp tubes when swapping or replacing them? 

[django7866]

From what I understand about preamp Tubes is you should always have them biased just from what my amp tech told me, I had all four replaced on my 77 model T. If your looking for a cleaner tone you may want to swap out your power tubes. Again, from what I understand is that certain tubes will give you more "headroom" which will allow for turning your amp up keeping it more clean before it starts to break up. What kind of power tubes do you have in? I really do have a clue as to what Power tubes would work for this. The reasons for asking, is you may want try a different brand. The Tung-Sol 6550/KT88 are great! I use those in my 74 model T in my 77 I have some Cheap russian made one, and they seem to break up after I turn up past 3/4. Maybe some one will chime in, that could be more help.

[Walt-Dogg]

It's the power tubes you wanna change and then maybe the pre-amp tubes. You're gonna wanna get some cooler (as in less hot) running tubes, the less hot the tube, the cleaner the sound. And getting the amp rebiased for the tubes is a must. If your amp isn't clean enough after changing the power tubes you might want to then change the pre-amp tubes or maybe go for some cooler running power tubes. I've done this with several amps. I've bought tube amps with tubes for super high gain and changed them out for low gain tubes and vice versa. Always had them biased.

Just take your amp to a tech, ask his opinion and he can tell you what tubes you're gonna want to try. It's all personal preference, but let the expert help. I would suggest taking his opinion though deciding on what tubes, buying them yourself then going back to the tech. (It will be cheaper to pay for the tubes yourself, and only pay the setup fee. Not all techs charge wholesale on parts and $50 flat for working on the amp, no hourly like mine.)

[chris348]

try putting some 12at7 in your amp
http://www.300guitars.com/articles/preamp-tube-gain-factors-and-substitution-chart/