The Huffer: schematic inside.

[brad]

I thought I'd repost this design from my space charge tube experimenting dayz.  This circuit is one of my favorites, because not only is it super simple, but it also made my p-bass sound fresh and alive (or in mojo terms: "solid gold tone!").  Oh, and to clear up any doubts about using 12v with a tube, the 12AJ6 is designed specifically to run at its best at that voltage. 

I haven't shown the heater connections or tube pin numbers, so here's the datasheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/1/12AJ6.pdf -the tubes are actually quite small and have 7 pins.

Preemptive FAQ:
Q: "Where do I find those tubes?"  A: On eBay.
Q: "What filter caps do I use on the power supply?"  A: Any large value electro will do.
Q: "How much boost is available?"  A: Not enough to call it a booster.

[bioroids]

Seems cool and pretty simple to try, thanks for sharing!

Miguel

[MR COFFEE]

Got any clip we can listen to ? Your mojo description sounds interesting

[evertonberger]

Hi man super cool this schematic one question??? there is a mosfet in the schematic?? This add some gain in your signal??
Thanks

[Tubebass]

What looks like a mosfet in the diagram is actually a pair of signal diodes within the tube. Have a look at the datasheet and all should be clear.

[brad]

Yep, it's not your typical guitar tube.  They were originally used in car radios in the 50's! 

[RaceDriver205]

Sound clip, sound clip, sound clip!

[brad]

What do I look like?  A pedal salesman?

[timo]

Sweet! I already got myself some 12AJ6:es and sockets only to find out that your page with the schematic was gone. Thank you so much for reposting it!

By the way I think you said somewhere that a 33k resistor worked even better for the grid resistor - or the grid resistor value changed the tone somewhat. Would a 33k resistor in series with a suitable variable resistor work as a tone control?

[brad]

Oh yeah, I completely forgot about the 33K thing.  I suppose you could try using the input resistor as a type of tone control...it wouldn't hurt to try.

[moosapotamus]

Looks cool, Brad... nice and simple, too.

What do you run the heaters at, 12V?
I see you tested with a 1A supply. Do you know if it could get by with less, maybe ~200mA?

Thanks
~ Charlie

edit: Oh... OK... reading the datasheet now... thx!

[nordine]

great!

i did almost the same experiment once, got the 12AJ6 and put it in a modded fetzer circuit... i would like to know what exactly does it to the signal.. indeed you get a "fuller" sound.. compression?

[Bernardduur]

Awesome!

Will try this one for sure!

[syndromet]

I'll try this one too. I ordered the tubes earlier today, and I just saw that I ordered 12au6 instead of the 12aj6..... Anyone knows any good projects for a 12au6? Anyone have a data sheet?

[moosapotamus]

Anyone have a data sheet?

Try the data sheet locator at duncan amps... http://www.duncanamps.com/

~ Charlie

[brad]

great!

i did almost the same experiment once, got the 12AJ6 and put it in a modded fetzer circuit... i would like to know what exactly does it to the signal.. indeed you get a "fuller" sound.. compression?

I don't know exactly how to explain it, but I tested it using a 100w Fender SS amp and a P-Bass with dead strings and it made the strings sound practically fresh again.  I do recommend tweaking the input resistor to taste though.  On my particular bass 68K had a more "stringy" tone and 33K was full and balanced sounding.

[timo]

Try the data sheet locator at duncan amps... http://www.duncanamps.com/

~ Charlie

Or go straight to http://www.tubedata.org/ (25000+ datasheets) 

[MR COFFEE]

Hi Brad,

I'm sure RaceCarDriver205 sand I aren't the only one who'd like to hear clips. Could you do one if you haven't already and post it for all to hear what this tube does for your bass?

Thanks !

[RaceDriver205]

Hell yeah! Sif not b fully l33t and hook sup wit sum clips noob.

[sfx1999]

Try using an op amp to boost the signal into it.