[ZRGuitar1993]

Hi there,

I recently found a box of about 150 old 12SN7 GT tubes from various brands.

I was wondering if anybody knows of a good preamp circuit that uses this?

I'm a guitar player, and I have experience building overdrive circuits. When I found these, my first thought was to use them to make a tube overdrive guitar pedal, but from what I've read, these aren't very high voltage. If I could use them as a microphone preamp, or perhaps a tube phaser, I'd be very interested in that as well. Hoping that someone has some insight into this.

I've never made anything that required a tube (or transformer) in it, so that will be new to me but I'm extremely familiar with soldering, schematics and using the various other components that would make up a typical circuit.

I did find one preamp schematic online, so I will likely be building that first, just to see what these will do.

Thanks for any tips/insight

[TomS]

The Linear Tube Audio MicroZOTL preamp uses two 12SN7's

[sunnydaze]

Mapletree Audio.

Definitely not audio-dweeb glitz, but simple direct circuits and cases.  No personal experience but reported to be musical and organic.  Very reasonable prices.

https://www.mapletreeaudio.com/

[JohnR]

I recently found a box of about 150 old 12SN7 GT tubes from various brands.

I was wondering if anybody knows of a good preamp circuit that uses this?

Hi, the 12SN7 is the same as the 6SN7 except that the filament is 12.6 V instead of 6.3V. So any circuit for the 6SN7 will work but substitute 12.6V (or 12V) on the filaments.

[grubyhalo]

If you want a documented design with board and other parts:

https://glass-ware.stores.yahoo.net/paraikocster.html

[richidoo]

Aikido preamp designed by John Broskie. PCBs sold on his website

Aikido circuit is also used in the preamps and kits sold by Vacuum Tube Audio

The VTA PCB is used in the much loved Don Sachs preamp. Aikido is a distortion cancelling design with clear musical presentation. When built with octal tubes like 6SN7 or 12SN7 it sounds very nice indeed!

Broskie's instructions explain how to set it up with almost any combination of tubes. He offers complete kits now too, or its without tubes.
Good luck with whatever circuit you decide.

Looks like grubyhalo just beat me to it!   

[DaveC113]

The Aikido is very hard to beat and it works great as a driver section for an amp too.

I think Broski now has a tube rectified PCB, if I was to change anything I'd probably go with a tube rectifier on my two Aikidos.

Also, I'd consider using Clarity TC caps for the power supply, at least in the last stage. Makes a big difference vs electrolytics.

[rockadanny]

Mapletree Audio.
Definitely not audio-dweeb glitz, but simple direct circuits and cases.  No personal experience but reported to be musical and organic.  Very reasonable prices.

I have one - love it. Musical and organic for sure. Can run either 6SN7 or 12SN7, which is a real nice feature. Red box behind is the tube-rectified power supply.

[sunnydaze]

I have one - love it. Musical and organic for sure. Can run either 6SN7 or 12SN7, which is a real nice feature. Red box behind is the tube-rectified power supply.

I've heard it while visiting friends that own it.  I too think it's great.  And I love the anti-audio jewelry-put-the-$$-where-the-sound is approach!     

[rotarius]

I had the Mapletree pre, tube rectified version.  I regret selling mine.  Hard to find used, I have been looking.  You can't go wrong with that one.