Tube Works Real Tube Overdrive 901 (better than I expected!)

[Steve A.]

I just picked up one of these figuring that I could rewire it as the original 4 knob Tube Driver but with the right tube it sounds pretty damned good. (It came with a very anemic Sovtek/TungSol 12AX7 and sounded like crap in the store.) I just ran across an interview with B.K. Butler who said that the RT 901 was an improved version of the original Tube Driver. (Pssst! Don't tell Eric Johnson about this.)

Tone From Heaven: B.K. Butler Interview

Here is a schematic of the RT 901:



The knobs are labeled as those in the 303. Push is Drive, Ice is Treble, Warm is Bass and Neutral is Midrange.

Although all of the B.K. tube overdrive-style pedals are starved plate he gets better results from that by connecting the cathodes of the 12AX7 to a minus 12 volt supply. (I'm not sure if that is better than just using a positive 24 volt supply to the plates.)

One question- any ideas for adding the bias control to the RT301? Here is a schematic of the Tube Driver Rev 2 with that control.



Steve Ahola

P.S. The RT301 sounded pretty bad in the store- it had a very anemic Sovtek/TungSol 12AX7 in it. I tried about 30 different tubes in it but ended up putting in an NOS 12AU7 as was suggested in an earlier thread here:

http://music-electronics-forum.com/t2397/

P.P.S. I found a reference to the factory schematic for the Chandler rack mount Tube Driver but could not track it down. Anybody here have it? Thanks!

[dai h.]

I think there was a schem for one (rack unit) at freestomboxes

[Steve A.]

I think there was a schem for one (rack unit) at freestompboxes

Thanks! It took awhile to find it among the 100+ posts over there but here is the schematic:

http://www.dirk-hendrik.com/temp/Cha...river_Rack.pdf

Here is a link to search for all of the Tube Drive stuff there (lots of good information!)

freestompboxes.org • Search

Another good thread:

http://www.freestompboxes.org/viewto...=+tube+driver+

Steve Ahola

P.S. I got one of the original Chandler/BK Butler Tube Drive stomp boxes in 1986- best dirt pedal ever- but I traded it in to get the rack mount version a year later thinking that it HAD to be much better- right? Nope. I should have gotten suspicious when they gave me full credit for what I had paid for the floor box- usually after a year I'd be lucky to half of what I paid for something.

My main recollection of the foot pedal (besides sounding great) was that I had thought that the treble control kinda worked like the frequency control in a parametric equalizer. But I have not seen anything like in any of the schematics.

In any case I wanted to make my rack mount TDR 101 sound more like the floor pedals (which was why I was looking for the schematic.) I bought 2 or 3 TDR carcasses from Dan Torres for $15 or 20 in the mid 90's so I could play around with those as well. So thanks for the tip- I'll post whatever I come up with.

[dai h.]

sry Steve, I suppose I should have looked it up for you if it was one of those hard-to-find threads!

re: the Tube Drivers, I've always wanted to check one out since (despite "starved plate" circuits seeming to be generally frowned on from a general tube head perspective) many "tone concious/tone-imitated" players (Gilmour (sp?), Eric Johnson, etc.) seem to make use(or have made use of) one. Hopefully, I'll luck into some cheap semi-broken but salvageable sort of thing one of these days. FWIW the 4-knob units seem to go for much more than the 3-knobbers (in the Japanese used market).

Also, as far as "starved" B+ circuits, might want to check out (at least for some interesting reading if not more) this one:

freestompboxes.org • View topic - What do you think about low-volt tube pedals?

where merlin generously chimes in and shares some thoughts and bits on getting *more* linearity (rather than the usual less) from low voltage tube circuits.

[Steve A.]

sry Steve, I suppose I should have looked it up for you if it was one of those hard-to-find threads!

No complaints- you sent me to the right site and I enjoyed reading through all of the posts. In looking at the various B.K. Butler schematics there was one part missing on the RT901/903 board: when a 500kA is used for the treble pot he almost always adds a 220k resistor from the pot wiper to the "cold" outer terminal (the terminal that is connected directly to the bass pot.) It might have been left out because there was not a lot of room for it- I have a hunch that the PCB was already plotted out and he discovered that he forgot to include the tapering resistor. In any case it was fairly easy to add the resistor to the backside of the board (the side with the LED's). The resistor is added between the middle terminal and the terminal right next to the output volume pot. There were little stubs sticking out so after removing the solder I wrapped the leads of a 1/4 watt 220k resistor around those stubs and soldered away. NOTE: it would have been much easier to fit in an 1/8 watt 220k resistor and with the low voltage and current there should have been no problem.

The board design is really slick! He has the EQ pots mounted on the component side of the board and the volume pots on the copper side- all of the copper pads are in a row with an equal distance between them. The two LED's are mounted on the outer edges of the board. (It would have been a real nightmare had he used chassis mounted pots- the wiring would be a big jumble.)

The interview with BK Butler was very interesting. He started working on a tube overdrive box in the late 70's- he was designing them for keyboards not guitar, to get the overdriven sound from Leslie speakers. He considers himself to be more of a musician than an engineer- I think that he kept experimenting around until he came up with something that worked really well with low voltages. Rather than starting with the math and then trying to apply it to the musical needs.

He started making the Tube Overdrives again- he is using better components and think that they are better than the old pedals that sell for more ($300 new plus $125 extra to add the bias control.)

Tone From Heaven: B.K. Butler Interview

I couldn't find any schematics for the 3 knob version.

Steve Ahola

[dai h.]

maybe this one (sry haven't checked it out close, just a result from a quick google) :

http://www.muzique.com/schem/tubedrvr.gif

[Steve A.]

maybe this one (sry haven't checked it out close, just a result from a quick google) :

http://www.muzique.com/schem/tubedrvr.gif

Thanks! I looked up patent #5022305 and snagged these two pages showing the circuit and the power supply. In the 2006 interview B.K. Butler said he designed the 3 knob Tube Driver as a lower cost alternative for musicians looking for a tube overdrive pedal.





The patent application itself is very interesting and it can be viewed at Google Patents (which sure beats the old way of searching and viewing patents using AlternaTiff... )

Patent US5022305 - Tube overdrive pedal operable using low voltage DC battery eliminator - Google Patents

Steve Ahola