[RipVanWinkle]

So...last week I bought a 12at7 preamp tube.

From everything that Ive read and heard, people suggest putting these in the V2 spot...Primarily to help with distortion. Well, I put one in the V2 slot. I didnt think it sounded that great. On clean, the tube would start to break up at around 4. I didnt think that it would change the clean channel that much. I didnt like the sound I got. Then, I couldnt get a nice sounding distortion.

So...

I put the 12at7 it in the V1 slot and put a 12ax7 back in the V2 slot. Now the amp sounds SO much better to my ears. The distortion even seems smoother. Does this sound right? Im following these diagrams from http://studentweb.eku.edu/justin_holton/faq.html#preamp




So...possibly the lower gain of the 12at7 driving into the 12ax7 makes the distortion not as harsh?




I dont really know that much...YET... so somebody help me out.

[Major Tom]

You're the first one I've heard from who did that "mod" and didn't like the results better than the stock config.....

When I put the lower gain tube in V2, I didn't notice the clean channel sounding any different - its not really changing it all that much. In fact, I thought it was a relatively subtle change for the Drive channel, mostly noticeable in a reduced amount of saturation at low gain settings. If its breaking up at 4, it sounds like its beign fed a boosted signal...what kind of signal you are putting in - straight from the guitar? What kind of pickups? buffered pedal? Multi FX? If its boosted, how much? Are you using the FX loop?

A couple things come to mind:

The strength of the signal being fed into the input has a lot to do with the overall gain. IMO, it sounds best with a passive guitar level input, about the output level of a stock single coil strat or tele. Are you using input #1 or #2? #2 has a lower impedance and is there for higher level signals, like from a multiFX or whatever. For whatever reason, and maybe its my imagination, but that input never sounds as good to me when I use it as intended;with an active input source. I think it sounds better turning down the level of the multi FX to about the level of a strat, for example, and using input #1. With a hotter input signal, V1 may be a good place for the lower gain tube.

Where were the eq controls set? with the lower gain tube in V2, you may like it better with them turned up.

As far as your question - the input level at each stage determines the output level at that stage; the more input, the more output. The more output, the more distortion and saturation will occur in all the subsequent stages - all preamp stages, the phase inverter, and the power tubes. The level of the signal into the input of the amp is critical in determining the overall gain of the amp. For tube amps that I have messed with, to me they sound better with a very modest input - too much signal at the first level causes too much saturation.

And of course, as always, taste in amp tone varies

[RipVanWinkle]

Well, I was running the charvel straight into the input #1.

I played with it alot at home, and my pedals stay at church. Im loving the sounds I get now...When I put the ax7 back in, it seemed to seat deeper into the socket...could a half-seated tube mean bad performance? I doubt it was actually so, but Im kind of stumped too.

[nate95366]

Originally Posted by RipVanWinkle

could a half-seated tube mean bad performance?

From my experience, half-seated-tubes often lead to bad performance. It's especially true of the power tubes, but the preamp tubes need to be in there all the way, too.

Nate

[Major Tom]

Originally Posted by nate95366

From my experience, half-seated-tubes often lead to bad performance. It's especially true of the power tubes, but the preamp tubes need to be in there all the way, too.

Nate

Absolutely.

With the guitar going straight in, and getting breakup on the clean channel at 4, especially with a lower gain tube in V1 indicates to me there is/was an issue.

[Major Tom]

Oh yeah, a couple other things popped into my head-

It could be an issue with your Phase inverter tube V3. Tubes vary a lot within the same brand/type as far as gain and current. The current capability is much more significant in the PI position, in fact, back in the old days they used to use high current tubes like the 12AT7 (which has the capability of something like 8 times the current of the 12AX7 and other preamp tubes) for the PI. I read an article about it a few months back, one of the tubes that was recommended for the PI was the Sovtek 12ax7LPS - it has a bit more current capability than some other 12ax7's.

Another suggestion for your amp (even though the last one didn't work out so well ), and tube amps in general; at least give it a try. The Presence control is not just an eq control per se, like the treble, bass, mids of the tone stack. The presence cuts the amount of the negative feedback loop (NFB), at a certain freq. and above. I don't understand the need for NFB, but essentially it is a circuit that injects some of the amp's output back into an earlier stage with the phase reversed, which cancels out the main signal somewhat. It reduces gain, its whole purpose is to achieve more clean headroom. Anyway - I like to turn the Presence all the way or most of the way up, it gives a different characteristic to the distortion. On the clean channel, it is said that it will result in a smoother transition from clean to breakup. It does add a bit of gain, and the amp wil break up just a bit earlier. Turning it up of course results in more highs - I just leave it up and turn the treble control down to tame the highs. The Vox AC30 and I think the AC15, with the exception of boutique amps, are the only "popular" amps that I'm aware of that were designed with no negative feedback loop. One amp guru stated that he thought that was the single most significant contributing factor to the "Vox sound".

[RipVanWinkle]

Hmm..

I'll have to check some of that stuff out tomorrow. Ive had the presence (up until now) down at almost 0 or 1.

[RipVanWinkle]

Yeah...

I did much more testing...I dont know if I just have a wacky v2 spot...I dont know.

With the 12at7 in V2 it does, in fact, breakup on clean at around 3 or 4. Almost I mean...it was very overdriven. I reseated the tubes many times just to make sure I had everything right.

I put it (12at7) back in V1 and I can go up to around 7 before breakup begins. From what your saying, tom, is that I should get the exact opposite effect. Everything smooths WAY out with it in V1.

I would have guessed that even though the tube was MESA, it would just be a chinese rebrand...I still think it to be the case, but now Im pretty stumped.

[edit]: The Charvel has some crazy hot pickups (from what Ive read...I dont have a multimeter to test them). I still havent messed with the presence...I forgot to try it, and I left the amp at church after practice 2nite...Im way too busy to play it much before sunday.

[Major Tom]

Originally Posted by RipVanWinkle

Yeah...

I did much more testing...I dont know if I just have a wacky v2 spot...I dont know.

With the 12at7 in V2 it does, in fact, breakup on clean at around 3 or 4. Almost I mean...it was very overdriven. I reseated the tubes many times just to make sure I had everything right.

I put it (12at7) back in V1 and I can go up to around 7 before breakup begins. From what your saying, tom, is that I should get the exact opposite effect. Everything smooths WAY out with it in V1.

I would have guessed that even though the tube was MESA, it would just be a chinese rebrand...I still think it to be the case, but now Im pretty stumped.

[edit]: The Charvel has some crazy hot pickups (from what Ive read...I dont have a multimeter to test them). I still havent messed with the presence...I forgot to try it, and I left the amp at church after practice 2nite...Im way too busy to play it much before sunday.

I have no idea how hot those pickups are, but even PAF style humbuckers IMO can over-drive / over-saturate an amp for my taste, including my HR DeVille, so I cut the signal some before it hits the amp. I think between 3 andd 6 db. Getting breakup at 4 with the 12AX7 in V1 indicates those are some pretty high output pickups, and that hot signal is eating up all the headroom in the amp. Putting the 12AT7 in V1, its just lowering the gain - you can do the same thing by cutting the signal in front of the amp with something like an EQ pedal, or other active electronic unit with an output level control. One of the "gospels" that I preach about electric guitar /amps is signal level; its critical to understand and control it at every stage (especially the level fed to the amp's input) to achieve the tone you want. One thing I absolutely do not understand is the need, in this modern age, for high output pickups. IMO, they are more of a hindrance than anything. You could roll back the guitar volume, but that also rolls off high end and makes it muddy unless you have the "keep the highs" mod on the guitar.

Try this - put the original tubes back in. Where does it break up on the clean channel? Should be about 4. Try cutting the level of your guitar, to the point where it starts breaking up on around 6. Or use something like a stock strat or tele - single coils. Now with those same settings, try the lower gain tube in V2.

The other thing it could be, or could be in combination with the hot level slamming the first stage, is the phase inverter tube; if the first stages are getting slammed, it in turn is also getting slammed, it may not be able to supply enough current under those conditions, which will cause a "bad" type of distortion. Try the 12AT7 in there, see what that does. The AT is a high current tube - like 8 times the amount of current of AX and other preamp tubes.

Are those active pickups?

[RipVanWinkle]

They are passive single coils



I wont have the amp to play with until Sunday, but I'll definently play around with it.