"Gain" in preamp tubes

[Fresh_Start]

When someone says "a 5751 in V1 will give you more clean headroom and lower the gain", what does that mean in practical terms?

"Clean headroom" seems to mean that you can get more volume before breakup/distortion starts, right?

But what does "lowering the gain" mean? Would I have to push the output tubes harder to get the same volume?

Sorry for these apparently stupid questions. I'm ordering new tubes for the Blues Jr. and am trying to figure out what makes sense for me. I don't need volume and prefer power tube distortion (using a Weber Mini-Mass) to preamp distortion.

Thanks for any help.

Chip

 

[JumpMarine]

Re: "Gain" in preamp tubes

On a gain scale of 0-100 a 12ax7 is 100 and a 5751 is around 70. Comparing the gain at the same volume setting: 12ax7=full gain (more saturation) 5751=70% of that gain (more headroom). I don't think that you will have to push the tubes to get more volume, just more breakup if that makes sense.

 

[jdm61]

Re: "Gain" in preamp tubes

7025/ECC083?12AX7's have the most. 12AU7's have the least, I do believe. AT's and AY's are in between. 12AX7's are also dual triode, so some amps will use half of the tube for one function and half for another. My Vibrolux splits at least one tube.

 

[Quencho092]

Re: "Gain" in preamp tubes

the volume is a bit lower. For example your amp at 2 with 12ax7's will be a bit louder than your amp at 2 with 5751's. With 5751's you lose some sparkle off the top, which is why i steered away from them eventually, but they can keep an amp cleaner if you're looking for jazzier or smoother tones without getting loads of preamp grit all the time.

Personally, i just dial back a tad on the volume knob of my strat and it turns the agressiveness of the amp back a notch.

 

[idsnowdog]

Re: "Gain" in preamp tubes

5751's are a different beast that can be used instead of 12ax7's. I like using 5751's in latter stages because they distort like a power tube rather than a preamp tube. They give off a distinct growl with strong harmonics.

 

[jdm61]

Re: "Gain" in preamp tubes

And to add to the confusion, 7025's are low noise mil-spec tubes that are pretty much direct replacementy for 12AX7's. But if you have a blackface Fender that uses the AB963 circuit, you will see that the chart may call for both types:eek13:

 

[idsnowdog]

Re: "Gain" in preamp tubes

The problem with 7025's is that they are annoyingly clean! Pretty hard to get one to break up nicely. A good tube though for audiophile use where you just need clean tube volume.

 

[Fresh_Start]

Re: "Gain" in preamp tubes

Found a good reference to answer my question: http://www.thetubestore.com/gainfactor.html

Chip