Can power tubes such as EL34 produce high gain distortion like a Mesa preamp?

[thinkingchicken]

"In some respects, a tube is just a tube: we could cascade 5 or 6 EL34s in a preamp-like circuit to mimic a master-volume preamp, where each stage contributes a little distortion per stage to build up a smooth high-gain sound (just like a Mesa preamp, or a SLO preamp, or a Marshall preamp, etc). Nobody does this because it would cost a lot more than using the usual small-signal preamp tubes, power supply requirements would be obscene, and a preamp for our "power-tube preamp" would be required to get signal levels large enough to drive each tube to distortion.

- Just because nobody does it because "it's a bad idea" or "too costly" doesn't mean no one will ever build a one-off for themselves that uses power tubes for a "high-gain preamp." I knew a guy who built an inverted mode amplifier where the input to the power stage is applied to the plate, and the output is taken from the grid, then sent to the speaker. It's a "stupid way to operate a tube" because available power output from the tube is severely restricted, but the guy did it because it 1) eliminated the requirement for an output transformer, and 2) he wanted to see if he could make it work. After making it work, he tore down the amp & re-used the parts for some other project."


That is an interesting thought experiment where instead of using 12AX7 tubes in the preamp stages in a high gain guitar amp, how about using mutiple preamp gain stages with six or more EL34 tubes given that we have enough power supply, enough signal levels to drive the EL34 tubes to high gain distortion, everything's enough, etc.

Imagine if someone succeeded making such preamp, can the EL34 tubes actually produce high gain distortion like a Mesa Boogie Dual Rectifier preamp despite the differences between EL34 and 12AX7?

[roberto]

What is the benefit you see of having EL34 distortion compared to properly designed 12ax7 OD channel?

[Stevem]

The term power tube references there needed design of adding high levels of current to the audio signal passing thru them, gain wise as in the signal gain you speak of certain tubes like EL34s and 84s have the highest level of gain that the most common output tubes used in guitar amps have, but this at best only matches the gain level of like a 12AU7 preamp tube with a gain level of 17 out of 100.

[thinkingchicken]

What is the benefit you see of having EL34 distortion compared to properly designed 12ax7 OD channel?

It is just a thought experiment. I wonder if a preamp circuit with six EL34 tubes, with enough power supply and enough signal levels to drive the EL34 to distortion, can actually generate a high gain distortion of a typical preamp with 12AX7 tubes.

[thinkingchicken]

The term power tube references there needed design of adding high levels of current to the audio signal passing thru them, gain wise as in the signal gain you speak of certain tubes like EL34s and 84s have the highest level of gain that the most common output tubes used in guitar amps have, but this at best only matches the gain level of like a 12AU7 preamp tube with a gain level of 17 out of 100.

So, even if someone succeeded in making such preamp circuits with six EL34 tubes, the distortion that it produced will not sounds like the high gain distortion that is produced by a typical Mesa preamp with 12AX7 tubes because of the differences in characteristics and the limitations of EL34 when used as preamp tubes?

[thetragichero]

dang, posting this here too?

[thinkingchicken]

dang, posting this here too?

Hey its you yes I need to hear different opinions too.

[Phil_S]

This is ridiculous. There is a saying, get the right tool for the job. Yeah, I can saw wood with a dinner knife (the kind with something that almost passes for teeth) and eventually, I'll slice it up. That Japanese pull saw I've got will make quick work of it and that's that. There are many tube choices. Each one has different characteristics. Choose the best ones for the job. Go ahead and cut your lumber with a dinner knife. It if pleases you, who am I to say don't do it.

[thinkingchicken]

This is ridiculous. There is a saying, get the right tool for the job. Yeah, I can saw wood with a dinner knife (the kind with something that almost passes for teeth) and eventually, I'll slice it up. That Japanese pull saw I've got will make quick work of it and that's that. There are many tube choices. Each one has different characteristics. Choose the best ones for the job. Go ahead and cut your lumber with a dinner knife. It if pleases you, who am I to say don't do it.

Lol you said it the best. I get your point (Dinner knife = EL34, saw = 12AX7). Thus, an EL34 as a preamp tube even with its normal volts can't compete with a 12AX7 when it comes to distortion.

[stephenl]

Try it, then you'll know for yourself if it has any merit.
No harm done as long as the tubes are used within their ratings.

[thinkingchicken]

Try it, then you'll know for yourself if it has any merit.
No harm done as long as the tubes are used within their ratings.

It is just a thought experiment. The cost will be unbelievable and it will be very difficult to make such preamp as others have pointed out. Even if we succeeded, there's no guarantee whether it will sounds just like a typical preamp with 12AX7 or not.

[Stevem]

Even if they could produce the same level of distortion, the distortion that triodes ( preamp tubes ) produce does not have the same harmonic content to them as the output tubes do since they are tetrodes or pentodes.

Triodes when they are pushed into clipping have higher levels of what called even order distortion, output tubes can have higher levels of odd order distortion, or a more even mix of such!

[thinkingchicken]

Even if they could produce the same level of distortion, the distortion that triodes ( preamp tubes ) produce does not have the same harmonic content to them as the output tubes do since they are tetrodes or pentodes.

Triodes when they are pushed into clipping have higher levels of what called even order distortion, output tubes can have higher levels of odd order distortion, or a more even mix of such!

Sorry isn't it actually depends on the type of the amp? If it is a single ended amp, regardless of tubes, it will sounds even-order harmonics dominant and if it is a push-pull amp, it will sounds odd-order harmonics dominant?

[teemuk]

Well said about picking the right tool for the job.

EL34 is a great tube for power amplification at "high" levels of current but does not excel with its capability to amplify voltage (in great ratios). Matching that to performance of 12AX7 as a preamp gain stage (or vice versa) is therefore not trivial and is an engineering challenge in its own feat. You could choose "preamp" pentode tube, such as EF86, and achieve better results in this regard. (Though ironically there aren't many examples of using them for distortion, which IMO tells its own tale how much contribution one can expect from swapping triode to pentode).

As said, I wager that if clipping thresholds are biased reasonably close and voicing is the same audible difference of triode and pentode is very slight. Not neccessarily worth bothering. The overall circuit contributes much more than the device.

As for overall characteristics... those of pentode tubes are extremely close to those of FET transistors and FET based "preamp style" emulations of classic tube preamp designs (or preamps of their own merit like Randall RG100ES) are quite popular. Yes, high gain is definitely one application). Does that shed any light to your thought experiment...?

[thinkingchicken]

Well said about picking the right tool for the job.

EL34 is a great tube for power amplification at "high" levels of current but does not excel with its capability to amplify voltage (in great ratios). Matching that to performance of 12AX7 as a preamp gain stage (or vice versa) is therefore not trivial and is an engineering challenge in its own feat. You could choose "preamp" pentode tube, such as EF86, and achieve better results in this regard. (Though ironically there aren't many examples of using them for distortion, which IMO tells its own tale how much contribution one can expect from swapping triode to pentode).

As said, I wager that if clipping thresholds are biased reasonably close and voicing is the same audible difference of triode and pentode is very slight. Not neccessarily worth bothering. The overall circuit contributes much more than the device.

As for overall characteristics... those of pentode tubes are extremely close to those of FET transistors and FET based "preamp style" emulations of classic tube preamp designs (or preamps of their own merit like Randall RG100ES) are quite popular. Yes, high gain is definitely one application). Does that shed any light to your thought experiment...?

It's nice to see you again.

Yes, I think those small-signal pentodes will be much more suitable than EL34. The generalization is that those small-signal pentodes generate mostly odd-order harmonics, while triodes produced even-order harmonics. But this can be changed by tweaking the circuit, isn't it? Do you think this book is a good source http://www.ken-gilbert.com/images/pdf/tvt.pdf? According to this book, the transistors produced the most symmetrical waveforms compared to the others. But I'm sure there are differing opinions out there.

"those of pentode tubes are extremely close to those of FET transistors"

So that explains that when the pentodes are overly driven that they finally generate a square wave on the scope, they sound like a fuzz pedal?