Hmm... Anyone try to make an overdrive pedal using an EL84 powertube?

[KerryF]

Would this be possible anyone?  May break up different than a preamp 12AX7 in a pedal.  Anyone try, any idea how, any suggestions?

Kerry

[brett]

Hi
you need a large input signal (about 20VRMS) to overdrive it (the pre-amp couldn't be an op-amp).
Probably best to drive it with a 12AX7.  But then you've got a Marshall 18W.
Other problems include the large bias current and high plate voltage.

[KerryF]

^-ok then. theres always the good-old fashion emulating. 

[JimRayden]

Check out the AX84 forums, there has been quite a few threads about using a power tube in a preamp. I think there even was a schematic using a 6V6.

And brett is right, it has to be driven by a high-mu tube to achieve the overdrive.

All in all, lots of experimenting to be done in this area. Who knows, some playing around may result in some of the best OD sounds ever. Then again it will be difficult enough to mach Marty's Tornado.

---------
Jimbo

[brett]

Hi
Not what you asked, but I've got another "tube overdrive" challenge for you. 
Build an OD using the 12U7.  Not the 12AU7, but the 12U7, which runs at plate voltages of 12V (it was designed for car radios).  They bias ok with a 47k plate resistor and 4.7k cathode bias resistor, but the gain is low (about 4) and the overdrive sound is weak, even if driven by about 1V RMS.
If you get good tones out of a 12U7, you'll be a tru legend, saving us from all that high-voltage mess of regular tubes.
cheers

[KerryF]

^-Send me one and I will do it for ya 

[JimRayden]

I've been dying to get my hands on one of these. Anyone know a source in Europe?

--------
Jimbo

[MartyMart]

There's a tube specialist in Germany who supplies these, can't for the life of me
remember, but a friend of mine Jan , who builds and repairs tube amps will know.
I'll drop him a line.

MM

[puretube]

http://www.amptone.com/hkcrunchmaster.htm

http://www.die-wuestens.de/

[JonFrum]

Pentodes designed to be used in preamps are called "sharp-cutoff" pentodes. EF86 and 6SJ7 are examples that have been used in guitar amps. I think Dave Jones built a pedal using a 6SJ7 - try a search over at ax84.com. There are smaller tubes, like the 7 pin 6AU6. Those 12V tubes mentioned above are another good idea. Using an EL84 in a preamp would be like trying to make a cat bark - theoretically possible, but the cat won't appreciate it