ef86 preamp pedal

[JoshBernstein]

Ive been craving that ef86 sound for a while, and i was wondering if it would be possible to build a separate ef86 unit or pedal to run into my amps. If so, does anyone have a schematic or layout for one? Thanks!

[stretch2011]

That's a simple one.
Take a known amps preamp section and put it into a pedal. Find a power supply that will give you roughly the voltages you need.

[sliberty]

Might actually be less microphonic in a pedal too.

[SilverFox]

Here are some suggestions:

http://www.dougcircuits.com/EF86.html

silverfox.

[davent]

Wouldn't kicking around a notoriously microphonic tube mounted in a pedal be troublesome?

There was a pedal schematic around using a 12sj7 pentode, i think it was Dave Jones that drew it up, same guy who did the Octal One and variants.

[JoshBernstein]

what is the best way to go about powering this? Wouldn't necessarily use it as a pedal, but more of a stand alone unit to put on top of my amp.

[sliberty]

Wouldn't kicking around a notoriously microphonic tube mounted in a pedal be troublesome?

There was a pedal schematic around using a 12sj7 pentode, i think it was Dave Jones that drew it up, same guy who did the Octal One and variants.

Can't imagine it being worse that housing it in a combo.

[JoshBernstein]

should i just use a regular power transformer or try to run it in starved plate?

[pinkphiloyd]

Tube Depot has a PT for "one preamp tube" projects. HT and 6.3 v secondaries. A few weeks ago I picked one up myself just for kicks. Haven't decided what I'm going to do with it yet.

[ampgeek]

Check out the "Tube pre-amp in a pedal box" project here (Hoffman Amps):

http://el34world.com/schematics.htm#Tub ... pedal_box_

I built one a few years ago and it worked fantastically.

Note the power supply transformer "stacking" to attain the desired voltages.

Good luck,
Dave O.

[JMFahey]

Not much of an "EF86 sound" by itself, no vacuum tube lives in a vacuum (sorry, couldn't resist ) but in an amp, with its own circuit, EQ, speaker, cabinet, transformers, all of which are WAY more important that the tiny tiny influence a tube can have.

Maybe you like , say, a VOX amp and call that the "EF86 sound" but there's way more important differences than just one lonely gain stage.

To boot, tubes are flat from DC to several MHz, and basically behave the same unless clipping, so only real difference, which can be picked by ear, between an EF86 (pentode) and one section of 12AX7 (triode) is gain.

I bet that if you get two gain stages, a triode and a pentode one, both driving a volume pot, set to the same output level and switch back and forth, you can't tell one from the other.

[RockinRocket]

Tube Depot has a PT for "one preamp tube" projects. HT and 6.3 v secondaries. A few weeks ago I picked one up myself just for kicks. Haven't decided what I'm going to do with it yet.

Im glad I read this thread. Is it a bad idea to put the transformer in a 7x 5 x 2 box? I want to build a boost and am afraid putting it in side will be noisy.

[SilverFox]

Hoffmans build is a good project review. There is a small torrid transformer inside the box and all the circuit details are there to get a good start.

I really have to wonder how many of the big box amp and pedal models produced were simply scavenged from sites like this and Hoffmans, absent any real engineering on the part of the phony designer. I've worked in enough corporate environments to have seen the dingy conference room presentation with "Clock and Pen Holder" desk ornament, congratulating some sleaze ball engineer for work he sucked up like a carp, from another’s efforts.

silverfox.

[RockinRocket]

Hoffmans build is a good project review. There is a small torrid transformer inside the box and all the circuit details are there to get a good start.

I really have to wonder how many of the big box amp and pedal models produced were simply scavenged from sites like this and Hoffmans, absent any real engineering on the part of the phony designer. I've worked in enough corporate environments to have seen the dingy conference room presentation with "Clock and Pen Holder" desk ornament, congratulating some sleaze ball engineer for work he sucked up like a carp, from another’s efforts.

silverfox.

Maybe, but how much is there really to design? My boost pedal is basically going to be a true bypass fender clean preamp with a baxandall tone stack. Its heavily influenced by my Blackstar 12ax7 Boost pedal from a spec point of view but every time open it up I cant believe how much crap is inside it. It sounds good but is kinda noisy. More components than my 18 watt and plexi!

[RockinRocket]

Not much of an "EF86 sound" by itself, no vacuum tube lives in a vacuum (sorry, couldn't resist ) but in an amp, with its own circuit, EQ, speaker, cabinet, transformers, all of which are WAY more important that the tiny tiny influence a tube can have.

The 65 amps London pro from my understanding switches the 12ax7 and ef86 in and out of the front end and the 12ax7 cant seem to get the chimey highs the ef86 has. I keep hearing the circuit has more influence than the tube but I don't think you can get that 86 chime out of a 12ax7 with any component/circuit change.