BK Butler - Tube Driver  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
Bernardduur
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Post by Bernardduur »

Whaha, true!
BK Butler - Tube driver.JPG
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Post by tictac »

Does anyone know about the "Bias Control" that's available as a new feature? According to Butler it controls the amount of current draw of the cathode.... You're supposed to be able to dial in the bias for different tube types....

Seems like it would be easy enough to implement... a pot between the cathode and V- perhaps? :hmmm:

TT

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Post by tictac »

:oops: sorry for not doing a search first.... yep, it's a pot, Bajaman already drew up a nice schematic...

Funny cause I'm tinkering with my Bajaman tube driver after reading this thread just didnt realise he made some updates to the circuit... :slap:

TT

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Post by teemuk »

tictac wrote:Does anyone know about the "Bias Control" that's available as a new feature?
In older TubeWorks units (e.g RT-902 Real Tube Rack) the "Bias" control was simply a potentiometer wired as variable cathode resistor.

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Post by teemuk »

...oh, forgot to mention, quoted as being a feature that actually makes the distortion more tweakable and versatile.

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Post by whopperplate »

Thank you all for the wealth of info. I am working out the details for building one of these guys and I am I seeing correctly that only the hot is connected to the output jack, no ground? Is it connected via the input jack ground to chassis?

Another question, what would the effects be of increasing the drive and high pots from 500k to 1M? Some of the old pedals had this value and I am wondering about their tonal difference.

Thank you for the time!

Charlie

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Post by Dirk_Hendrik »

Drive: Even more gain. About double of the max you had with a 500k pot. Tone: You'll change the frequency characteristic of the tone stack.
Sorry. Plain out of planes.

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Post by whopperplate »

Dirk_Hendrik wrote:Drive: Even more gain. About double of the max you had with a 500k pot. Tone: You'll change the frequency characteristic of the tone stack.
Awesome, that’s what I was assuming more or less, thank you!

Does it shift the frequency response up or down? I have never been educated on the math of what’s going on. I appreciate all the help, thank you so much.

Charlie

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Post by whopperplate »

Still most curious about the grounding scheme

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Post by whopperplate »

Also from looking at the PCB photos it seems the red LED is wired with the cLED to ground after , rather then between the R16 and the LED as written in the schematic. can anyone please also confirm this? Thank you

Charlie

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