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Well, I wouldn't pay $300-500 for any OD pedal myself. Any suggestions for adding a bias control to the RT901? One schematic shows a 47k resistor, a 22uF cap and a 10k pot (wired as a variable resistor) in parallel on the cathode of the two tube stages. Here is a link to the schematic of the RT901: I might have to get a second Real Tube Overdrive to use my high gain and low gain favorite tubes. The EI had a really creamy distortion but did not clean up to a very clear sound- the tube that seems to do that the best is the 12AU7. The current production tubes which sounded the best to my ear was the EI 12AX7 and the GT5751M. Not unlike a 12AU7 on the unmodded pedal- kinda like that but on steroids!ĮDIT I did more tube rolling with the modded RT901 and found that a lot of tubes sounded really good with it. (I didn't try an EI but I imagine that it would have sounded good since they are a lot like the old Mullards.) With right 12AX7 and the 220k resistor mod the sound is very rich with all sorts of nice harmonics in there and great touch response.

With the 'missing' resistor added the pedal works really well with a 12AX7- I found that old RCA and GE tubes sounded great, current production tubes not so great. I used a 220k 1/4 watt resistor but an 1/8 watter would have fit in better and with the low voltage and current there should not be a problem.Īfter putting the pedal back together I noticed that the sound was kinda dull with the 12AU7 so I put in an old Mullard 12AX7 that sounded really nice during my tube rolling session the other day. After removing the solder I wrapped the resistor leads around the stubs sticking up and soldered them very quickly. I mounted it on the copper side of the board to the middle terminal of the treble pot and the terminal furthest from the edge of the board. (The added resistors brings the total resistance of the pot down to 152 ohms and also makes the taper even more logarithmic- I'd call it a 'super audio' taper.)Īdding that resistor was not too hard once I got the board out. In the other schematics whenever he used a 500kA treble pot he added a 220k tapering resistor between the wiper and the 'cold' terminal (the one that connects to the bass pot.) Without that resistor the pedal would tend to be very bright. Butler schematics I noticed that there was a resistor missing in the RT901. However I did have to keep the Treble control way down- like 2 or 3 out of 10- for all of the tubes I had tried.Īs I was looking through the various B.K. As recommended here an old 12AU7 (Amperex) worked very well. (If not I could always bring it back within 30 days for a full refund.) It had a very anemic 2005 Sovtek/TungSol 12AX7 inside. I just picked up a 1989 Real Tube RT901 at GC the other day- it sounded like absolute crap in the store but I figured that a little tube rolling would do wonders for it.

Favorite this post bk butler tube works real tube pedal