Tube amp valve positions - mojo?

R

ryanrobles

New member
It appears to me that the market for valves/tubes increasingly seems to be driven by a higher price=better tone ethos.
As the entire world seems to be in recession, I thought I would post this question.

Which tube positions in an average 100w head amp (4x6l6/El34, 4x12ax7,solid state rec for example) amp, have the most effect over the overall tone and therefore are more deserving of upgrade?

Is it power tubes or pre-amp tubes that "shape" tone?

V1, driver and phase invertor are all terms bounded around but it so confusing to know what is fact and what is "mojo".

Are there are any tubes positions within an amp that simply are not deserving of a NOS GE 12AX7, and would pefrom equally well with a cheap sovtek??

Let the debate begin!!

All thoughts welcome.
 
Re: Tube amp valve positions - mojo?

Don't knock those Sovteks... they're not as bad as people make them out to be.
 
Re: Tube amp valve positions - mojo?

Jay 77 said:
Don't knock those Sovteks... they're not as bad as people make them out to be.
Click to expand...

Indeed !! That's what this thread it all about. Used sovtex as an example in my post as they tend to be cheaper. No reflection on their quality.
 
Re: Tube amp valve positions - mojo?

As I understand it, the preamp tubes are going to shape the tone of the preamp, and thus also the overall character of preamp overdrive. V1 is going to have the greatest effect, and the following preamp tubes, if any, will relate to any subsequent channels and the cascading effect between them. Substantial changes can be made to the overall tone and dynamics by experimenting with the preamp tubes. However, many modern amps are designed around current production tubes, therefore replacing them with vintage tubes may not yield any great tonal advantage. On the other hand, a vintage or vintage styled circuit can be greatly enhanced by using some of the better vintage tubes. The general rule of thumb would be to find tubes that are close to the original tubes used in those types of amps. For example, a vintage Marshall will benefit greatly from some early to mid 60's Mullard ECC83's (12AX7), whereas a vintage Fender styled circuit will be greatly improved with a late 50's RCA blackplate 12AX7, as would have been found in the original tweed Fenders. Switching these around can bring some interesting results, but in general an old RCA isn't going to sound as good in a Marshall as a Mullard, nor does a Mullard sound as good in a Fender as an old RCA.

As for power tubes, they are going to effect the way the power stage interacts with the speakers, and the breakup characteristics of distortion when the amp is driven hard into the upper ranges of its power output. However, power tubes are much more fragile generally than preamp tubes, so the use of vintage power tubes has to be approached with caution, because many will not have travelled through the decades particularly well. Similarly to preamp tubes, matching the brand to the original spec yields the best results. However, finding old Mullards in matched sets is prohibitively expensive and difficult to do these days. Vintage blackplate RCA's are slightly easier to find, especially in the case of 6V6's, less so in the case of 6L6's. In general, the best suggestion would be to find a current production tube that will get the job done and be reliable. There are other brands of vintage power tubes to try, but they may well be beset with the same problems.

As for the phase inverter, this is probably the one position which is closer to being about functionality than tone, although many will argue that it has a distinct effect. Generally, the requirement is for a tube that has matched sides and is fairly hardy, because it will be doing plenty of work. The phase inverter should always be changed along with the power tubes for optimum operation. I imagine that the driver tube refers to a reverb driver. The most important thing here is to ensure that the correct type of tube is used, and it is arguable whether or not any particular enhancement can be made to the tone of the reverb by using a particular brand.

Hope this helps.




Cheers..................................... wahwah
 
Re: Tube amp valve positions - mojo?

ryanrobles said:
It appears to me that the market for valves/tubes increasingly seems to be driven by a higher price=better tone ethos.
As the entire world seems to be in recession, I thought I would post this question.

Which tube positions in an average 100w head amp (4x6l6/El34, 4x12ax7,solid state rec for example) amp, have the most effect over the overall tone and therefore are more deserving of upgrade?

Is it power tubes or pre-amp tubes that "shape" tone?

V1, driver and phase invertor are all terms bounded around but it so confusing to know what is fact and what is "mojo".

Are there are any tubes positions within an amp that simply are not deserving of a NOS GE 12AX7, and would pefrom equally well with a cheap sovtek??

Let the debate begin!!

All thoughts welcome.
Click to expand...

Most of these subjects are covered on my website in the tech tips, other bits of writing and in the downloadable tube primers which are free.

www.guitaramplifierblueprinting.com
 
Re: Tube amp valve positions - mojo?

ryanrobles said:
It appears to me that the market for valves/tubes increasingly seems to be driven by a higher price=better tone ethos.
As the entire world seems to be in recession, I thought I would post this question.

Which tube positions in an average 100w head amp (4x6l6/El34, 4x12ax7,solid state rec for example) amp, have the most effect over the overall tone and therefore are more deserving of upgrade?

Is it power tubes or pre-amp tubes that "shape" tone?

V1, driver and phase invertor are all terms bounded around but it so confusing to know what is fact and what is "mojo".

Are there are any tubes positions within an amp that simply are not deserving of a NOS GE 12AX7, and would pefrom equally well with a cheap sovtek??

Let the debate begin!!

All thoughts welcome.
Click to expand...

The later gain stages are more forgiving of lesser quality or simply noisier tubes - BUT - the Sovtek WB and WC tubes are pretty dang good all things considered. Even the Chinese 12AX7's are pretty good and quiet. The reality is, I have a collection of NOS, still boxed GE and RCA 12AX7's that I've had for years but they all tend to be a bit more microphonic in the V1 position than a newer Russian or Chinese tube - sad to say... One of these days, I'll end up putting all my old tubes up on eBay so the audiophiles can have fun...

I might also add, that for those who really rely on preamp tone shaping, the preamp tubes are *obviously* going to have more of an impact on the ears - and that's where brand and model will really start to play a roll. Personally, I rely very little on preamp tone shaping or distortion (my pre is set on 2 and my master between 8 & 9) meaning you can get away with far more in the preamp section since all the "tone" is really being generated in the output section and controllable using my slave loads.
 
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Re: Tube amp valve positions - mojo?

V1 is usually the first gain stage of the preamp AFAIK. While there may or may not be more tubes in the preamp acting as gain stages, this 1st tube is going to have the greatest effect on the overall sound of the amp than the others. Any other gain stages in the preamp are going to be amplifying the signal produced by V1. Thus If you have a rather bassy tube in V1, you're going to have a bassy amp. If you have a noisy tube in V1, you're going to have a noisy amp.

Other preamp tube positions may or may not have as much of an effect on the sound depending where they fall in the amp's circuit(s) and what they do. The tonal properties of a tube driving the reverb in your amp probably aren't going to be heard if the reverb has been turned down to 0 or off. In a Mesa/Boogie Recto, V1, V2, V3, provide gain stages 1-5 for all channels, V4 drives the FX loop and V5 is the Phase inverter. So unless your're using the FX loop, you aren't going to hear what V4 sounds like. But in another amp this could be totally different. In a Mesa/Boogie Nomad V1 is gain stage 1, V2 is Channel 1 gain stages 2 and 3, V3 is Ch2&3 gain stages 3&4, V4 is Ch2&3 gain stage 2 and FX return and V5 is the phase inverter. In this design, you will probably not hear what effects V4 has on tone in channel one unless you're using the FX loop. In channels 2&3, you will never hear the tonal qualities of V2. Since Channels 2 and 3 are higher gain distortion channels, you can use preamp tubes that will sound better overdriven for those channels and a separate tube for Channel 1 which sounds best clean.

As for the thing with matched phase inverters, I'm not sure I buy into that. I've looked at the schematic for my amp and a few others and one thing I've noticed is components with different values than their counterparts on the other side of the power amp or components that have no counterpart on the other side of the power amp. Nevermind that the tolerances on some of these components may very well be wide enough that even the components with the same rated values on opposite sides of the circuit are mismatched. I don't think the circuit in the power amp is balanced to begin with, thus, what's the point of putting a balanced tube in your phase inverter position only to have that balance negated by a lack or balance in the rest of the circuit? So long as the tube in your phase inverter doesn't have a wild mismatch between sections (say, one side almost dead and the other side almost new) I wouldn't worry about it. I wouldn't be surprised if someone disagrees with me in this regard.
 
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