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What type of break-up does my amp have?

I'm really bad at understanding all of the science and technology behind tube amps, so I was wondering if one of you gentleman might explain to me how you can tell whether the beak-up is coming from the pre-amp or power section of the amp.

For example, right now I have two low-wattage tube amps (one made by Electrosonic Amps, the other by Thomas Winfield Amps) which are master-volume only. I presume that when I push the amps into overdrive territory that it's the power tubes that are breaking up?

But what about amps that have separate gain and master volume controls? If you turn the gain to 10 but leave the master volume at, say, 3, are you getting distortion from the pre-amp only?

:confused:

(And please don't ask me if my amps are Single-Ended, Push-Pull or Class A...whenever I try to really understand those concepts I feel like a preschooler at a neuroscience convention)
 

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You've basically answered the question yourself.If the amp only has a master or volume control,and you have to turn the amp all the way up to get it to distort,then it's power tube distortion.With a gain and a master,the gain pre-loads the preamp section and the master feeds it to the output section.It allows you to get distortion at a lower volume level.And like James Peters has stated,pre-amp distortion does not need to be buzzy.But unfortunately not all amp makers build their amps to sound like that.
 

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Unfortunately I can't tell when the power tube distorts on an amp unless I know its design already. It's possible as the "volume" is turned up, the preamp is distorting more (and the PI, if it exists, is also distorting), before the power tubes are distorting. At some point I'd assume the power tubes are distorting, but exactly where on the "volume" knob that happens, I couldn't tell you.
 

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Thanks for the info!

If I were to use pre-amp tubes that are supposed to be "tamer", i.e. 12AU7's instead of 12AX7's, would it affect how much gain I would get from my amps? That is, I presume that changing the pre-amp tubes would only affect the gain IF the break-up is coming more from the pre-amp section, and not from the power tubes?

And does the fact that the break-up is coming from the pre-amp section or power section affect how touch-sensitive the amp is?

Sorry if the questions are naïve or confusing...
 

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You need to identify what amp you have first.Is it a push-pull circuit or a single ended circuit?Then how many pre-amp tubes does it have? either way,the first 12AX7 is where the inputs are connected to unless you have a two channel amp.The pre-amp adds the gain to the circuit and the power section amplifies it.If you use a 12AU7 in the first pre-amp position it will lower the gain for the entire amp.It will have less volume and will likely break up less too.i would not suggest using a 12AU7 in any position other than the first ,because the loss of gain might be too much.Some amps respond very well to the change and other's lose too much.It will hurt nothing to try it.
The pre-amp sets the stage for the rest of the amplifier.It can be biased hot or cold just like the output section.
 

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Again, thanks for the info.

12AX7's it is, then. I'm not sure at all whether the amps are single-ended or push-pull, but they have exactly the amount of gain that I want, so I'll just leave 'em as they are!
 

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...in order to facilitate power tube breakup, would it make sense to use power tubes that break up early combined with preamp tubes that break up late?

i play through a traynor ycv40wr with (thankfully) no master volume on the clean channel.
 

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david henman said:
...in order to facilitate power tube breakup, would it make sense to use power tubes that break up early combined with preamp tubes that break up late?

i play through a traynor ycv40wr with (thankfully) no master volume on the clean channel.
Possibly. The sound of the amp will significantly change by doing that, and you still don't have complete control over when one type of distortion happens as opposed to the other.

FWIW, whether it's preamp or poweramp distortion isn't important. If you like the sound of the amp, that's important.

I know of an amp that has distortion which occurs in the following order as the volume is turned up--poweramp, phase inverter, preamp. When people use the amp, they love the sound of it turned up--when it gets the most preamp distortion blended into the sound. I find it a bit ironic since people associate the sound of that amp more with power tube distortion.
 
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