Tubeworks Tube Driver sounds like ripped speaker

[J M Fahey]

Shouldn't the grids have a negative voltage? I am not positive but is that part of how the tubes are biased?

In standard use, plates are positive by at least 90V , attract (negative) electrons a lot, tube would pass maximum current all the time, as much as cathode emission would allow, so we need a negative grid to *reject* those electrons and tightly control how many of them are allowed to pass through.

Now on these abominations, with only +4V (or +9v) on plates, electrons do not feel much attracted, if any at all, to make the trip to the faraway plate, so grid must be biased *positive* to at least "pull" some electrons from the cathode, which can then be attracted by the very weak plate voltage.
Anybody thinking this might work or sound like a regular 12AX7 might be interested in a bridge I have on sale now.

[guitician]

In the series filament arrangement if pin 5 is ground, then pin 9 should be 5v and that leaves 5v across the filaments. That is a little cold, but 10v from a 9v supply? Maybe use a 12v instead?

[km6xz]

Yes, Juan, it appears to be in "enhancement" but I doubt the schematic is correct. The saw-tooth waveform is unexpected so follow that lead. The tube in this configuration is not conducting until a positive potential is seen on the grid. The supply must not be needing to supply much other than heater at 1/2 the normal current, resulting in 1/4 the normal thermal emission. The sound quality will be obnoxious as drawn.

[Randall]

Please understand I did not build or design this pedal, I am simply trying to put it back to stock for a guy. For all I know, maybe I have already achieved this, not knowing how it sounded when it was made. I'm trying to get a proper schematic, and I am waiting for the owner to come give it a listen and tell me if it sounds right or not. I don't like the sawtooth on the second stage of the tube, however.

[Jazz P Bass]

Have you attempted to contact BK Butler?

[Randall]

Jazz, I sent an email to the address you provided a couple of days ago requesting the schematic. Have not heard anything.

[The Dude]

FWIW: I sold those things years ago when I ran a store and they always sounded grainy and gritty to me- more like fuzz than a "natural overdrive". I've not tried it myself, but many have said that they sound much better with a 12AU7.

[Jazz P Bass]

Jazz, I sent an email to the address you provided a couple of days ago requesting the schematic. Have not heard anything.

Call them.
Phone: 303-766-4504

[mozwell]

Randall
You say its a BK Butler Tube Works 3 knob, 9VDC version.

It will help if there are some pictures of the insides & outsides of this beast. Then we can know what we are looking at here.

The power supply may use a tripler or other such power supply, to get (say) 48V from the 9V supply. Hughes & kettner do this on cream machine etc

Is it also possible the unit requires an AC power supply, but someone has used a 9VDC power supply, and we now assume the 9VDC power supply is correct. Does the unit say 9VDC next to the power supply input connector ?

Does it look anything like any of the attached schematics ?

I know you are just trying to take it back to "original", and its not yours.
Dont be put off by the sawtooth, you can see all sorts of weird waveforms when the signal is highly over-driven & then filtered by the output filter (or even coupling caps).....

[MarkusBass]

Please understand I did not build or design this pedal, I am simply trying to put it back to stock for a guy.

And we are not trying to convince you to modify the pedal. I'm just trying to verify whether the schematic you posted is correct, or not. For me it is not correct. Can you verify whether it matches the PC board? If there is a reversed diode paralel to the power supply input, the pedal requires DC power supply (and this is just a protection diode against reversed polarity). Otherwise, it is possible that the pedal requires AC power supply.

Mark

[Jazz P Bass]

Hard to put it back to 'stock' without the correct information.

Keep in mind that this pedal was a transistion item for BK Butler.
Hand picked tubes for sure.

This pedal can be considered a hefty Tube Screamer, sound wise.
So it is in fact a distortion pedal.

From what I know, the Vac models had an onboard transformer.

[guitician]

Does it sound like this?

The demo drives the drZ amp so you really cant tell exactly how it sounds.

[Randall]

This one is close to the schematic I posted above, but not exactly. Mine looks t exactly like the one in the video above, and clearly indicates it is a 9 vdc pedal. I can't tell much from that video. And yes, this one definitely cares what tube it has in it. Customer said it started sounding bad, so he put a new groove tube in it, and that's how it came to me. I think I'll play around with a few more tubes to see where that gets me.

[teemuk]

So it isn't remotely a hifi stage.

Never was.

The solid-state stuff is there for that "HiFi". Tube stage with wacky bias and highly starved plate voltages obviously is not a very good choice for something like that. But it's obviously very easy to extract plenty of tube distortion from such.

Interestingly Butler's patent would actually present us some quite decent ideas of running tubes at those extremely "starved" voltages. More interestingly his practical circuits never seemed to employ any of those ideas.

And what's the idea of the "F.E.T." mode again? I can understand that in tube mode the signal passes through the "tube driver" stage but the F.E.T. mode simply bypasses that stage and does nothing else. Makes you wonder what that acronym even stands for. The same stuff is found from Butler-designed Dean Markley amps too and "works" exactly the same way. Most useless "feature" ever.

[guitician]

I looked at your posted voltages and it seems that the voltage drops across the two 220 resistors is too much, 10.1V DC to 8.3V DC. You may have a filter cap that is bringing the supply voltage too low.