General question about tube preamps and gain

 jj 12at7 :as the first gain stage or preamp tube  the nature of the 12at7 type tube is is a bit bright with a 60-70% gain factor.the nature of jj tubes is even with nice mids and not bright. a bit colourless and dull compared to nos greatest hits off course but not harsh like the chinese or russian tubes usually. ide use a 12ax7(100%gain factor) nos early 70's mullard 12ax7 i63(great low mids ) with low gain ratings or 5751(80% gain factor). that will raise the preamp gain which will result in earlier breakup or clipping and more overall output so if the breakup started at volume 5 now it will be from 3 or 4 so and you will be on lower volume with more of the tube’s gain in the sound and less of the circuit’s gain .the other option is opposite -to lower the gain : more clean range later breakup less overall output and then you can dial more volume  which is also nice and makes more sense in audio gear and angry guitar amps  i highly recommend mullard 70’s or 60’s 12au7 this type has more lows and about 30% gain factor so the added bass sort of makes up for the loss in preamp gain .within the 12at7 type you can also choose a higher or lower gain tubes and get less dramatic results . you don't need much knowledge or consulting the amp maker for swapping preamp tubes .

@f917025  I was under the impression though the pin outs are the same you cannot swap 12AT7 for 12AU/X7 tubes.

No?

gochurchgo, what you are asking makes sense. Putting a resistor downstream of the tube preamp isn’t all that different than putting a passive preamp downstream of the tube preamp. The only difference is that you get a “resistor” with volume control. If you did that, you could drive your tube preamp to full output and then attenuate the volume with the passive preamp. I’ve done this before. What I noticed was that the overall tone changed with tube preamp output level so with this setup, I could push the tube at a constant level and then control the volume with the passive preamp.

@mkgus  so if one were to do this, Would driving the tubes bring out more of what that particular tube imparts on the sound?

yes theoretically?

One other element to keep in mind is majority of the volume controls are nonlinear (logarithmic) and the degree of resolution increases as you turn up the volume. This is another reason for proper matching of the gain between the preamp and the amp to allow for the operation in the mid-upper region of the volume control range.