The 'magic' of the V1 pre amp tube

[Gold star]

I picked this up in reference to the late Stevie Ray Vaughan. his tech would change one of the pre amp tubes on his Fender amps to one with lower gain (usually 5751 ) in place of standard ECC83 so it would not distort too early on and give more clean headroom. But some advise against this as it can change the basic tone of the amp and affect other parts of the circuit too. It's been suggested the power valves then work harder-or run hotter to make up for this but I don't see how. Lower gain tube must mean it sends lower voltages to the power section in first place ? your thoughts...

[idsnowdog]

Re: The 'magic' of the V1 pre amp tube

I think the 5751 might have been in the second position? I have always used them in the second postion. The 5751 distorts in a very different way than a 12ax7 and a mix of the two creates nice overtones. You can use whatever you like. A champ with AU7 v1 and 5751 v2 is a great combo.

[ItsaBass]

Re: The 'magic' of the V1 pre amp tube

For almost 10 years now, I have been running a 12DW7 in the first 12AX7 spot of my main amp. I had trouble with too much early breakup on the amp, a 15W 1x12 combo. The milder tube helped quite a bit. The amp will never be a clean amp (which is why I like it), but I wanted it to start breaking up a little bit later. This seemed to do the trick.

[Demanic]

Re: The 'magic' of the V1 pre amp tube

The 12DW7 is a hybrid with one side 12AX7 and one side 12AU7, correct?
I think that I've tried one of those in my Picovalve. Went back to running 2 old National 12AX7's, but it didn't sound bad.

Sent from my Alcatel_5044C using Tapatalk

[Lake Placid Blues]

Re: The 'magic' of the V1 pre amp tube

It depends on which channel you plug into. Normal or Vibrato. On any of the brown or BF Fender amps he normally used the topography is simple.

For both channels it is: first half of 12AX7> tone stack (EQ) > second half of 12AX7 > Phase Inverter. There is no V2 between V1 for each channel and the power amp.

Of course a lower gain preamp tube will give a cleaner signal to the power amp. The amp might clean up better but still scream when he layed into it, because he's gonna be running the amp cranked. Another factor might be a cleaner signal through the tone stack after hitting the first half of the preamp tube pretty hard with a boost.

[Gold star]

Re: The 'magic' of the V1 pre amp tube

OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?

[ItsaBass]

Re: The 'magic' of the V1 pre amp tube

The 12DW7 is a hybrid with one side 12AX7 and one side 12AU7, correct?
I think that I've tried one of those in my Picovalve. Went back to running 2 old National 12AX7's, but it didn't sound bad.

Sent from my Alcatel_5044C using Tapatalk

I forgot the details, but it's something like that.

[JB_From_Hell]

Re: The 'magic' of the V1 pre amp tube

I don’t understand why the power tubes would work harder to “make up” for anything. Like they’re listening to what’s coming out, determine it’s not distorted enough, and kick into high gear to pick up the lazy preamp’s slack?

[Gtrjunior]

Re: The 'magic' of the V1 pre amp tube

I don’t understand why the power tubes would work harder to “make up” for anything. Like they’re listening to what’s coming out, determine it’s not distorted enough, and kick into high gear to pick up the lazy preamp’s slack?

I’m no electrical engineer but I agree with you here. Seems to me a preamp tube’s amount of gain is what it it is. The power amp simply works with what it is given.

[Lake Placid Blues]

Re: The 'magic' of the V1 pre amp tube

OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?

Your correct, what you read is incorrect. It won't harm anything. It may affect the sound or it may not depending on the amp and how it is being used. The 5751 just has lower gain compared to the common 12AX7. In a high gain amp that gets its distortion mostly in the preamp it could reduce the buzzy sound to the distortion that can often be a problem in a high gain amp.

The amps SRV mostly used depended on power amp distortion to get that sound. And he played very very loud, which is how you get power amp distortion going.

The exceptions would be his Soldano SLO100 that he began using shortly before his tragic passing, and/or his Dumble amps. In these such amps the use of lower gain tube in V1 or in V2 will have a profound effect on the gain structure of the amp. It could have been used to help that amp get a bluesier tone and to help tame the high gain nature of that amp, assuming they were speaking about a high gain amp.

Nevertheless, speaking in just general terms, the tube used in V1 of just about any amp is of vital importance, because it sets the tone at the beginning that will be amplified through out the rest the amp. Rolling in and trying different tubes, usually all 12AX7s, there as a trial and error processes, is a way of fine tuning the tone of an amp.

[eclecticsynergy]

Re: The 'magic' of the V1 pre amp tube

Re: power tubes working harder

I think it's just a matter of the amp getting turned up higher since the 5751 is giving a bit less gain in the preamp.

A little more of the drive tone would be from the power tubes vs the preamp, probably giving a slightly richer character to the breakup.

I like the sound of 6L6s running hot, but you seldom get to work them hard nowadays.

[Gold star]

Re: The 'magic' of the V1 pre amp tube

OK thanks..

[beaubrummels]

Re: The 'magic' of the V1 pre amp tube

OK. Electronics is complex so you read things that are not always correct. One post I read, (not here) suggested a lower gain tube in the first position can harm other parts of the circuit and make the power section work harder as it was not designed for something like a 5751 . I doubt it if people have tried it. In my case the amp is a single channel with single volume & gain knob . ECC83 / EL84 tubes. It's actually a Vox AC10 re issue. Is the 5751 tube of higher resistance?

If what you were saying were true, no amp would have a gain knob at the input, or running it on 1 or 2 would blow it up. IME, it works just the opposite.

[Gold star]

Re: The 'magic' of the V1 pre amp tube

The only thing I would add to that is how it (5751)distorts less in the first place ? externally it looks the same as an ECC83. I wonder if it has more resistance to the voltage applied. Maybe that's why some suggest it may have an adverse effect on other components..but again, people have tried it and not reported damage to their amps

[beaubrummels]

The 'magic' of the V1 pre amp tube

The only thing I would add to that is how it (5751)distorts less in the first place ? externally it looks the same as an ECC83. I wonder if it has more resistance to the voltage applied. Maybe that's why some suggest it may have an adverse effect on other components..but again, people have tried it and not reported damage to their amps

Tubes don’t have resistance. They operate on transconductance. The flow is regulated by a negative voltage on the grid.

The 12AX7 has a transconductance of 1600mhos, with a power factor of 100. The 5751 has a transconductance of 1200mhos with a power factor of 70. That’s why the 5751 provides less gain.