SHAKA TUBE HELP

[mrfirstime]

HI  its me againe.  Can some one please tell me what this is on the diagrame  of the power board that lead to the v+, V- and bias.  I have looked at the schematic and it looks like a pot.  If so where should it be turned to full or off.  Is there something else I could do there.  I will try to  put a pic of it hhere but not sure if it will work. Havent figured out how to put images in yet. 

[KazooMan]

It is a trimmer pot that is being used as a simple voltage divider to set the bias voltage for the tube.  I don't know what the desired bias is for this pedal, but I'm certain that someone will be able to help.  You adjust a trimmer with a small screw driver.  Tweaking the trimmer may change the sound from the pedal.  

You can get them from SmallBear.  They have three pins in the triangle arrangement you see on the layout.

http://www.smallbearelec.com/Detail.bok?no=160

[mrfirstime]

Thanks

Could I use a normanl 10 k pot do ya think

[KazooMan]

Yes, you "could" use a regular pot, but the size difference is enormous.  The trimmer will be about 3/8" square and about 1/4" high.  The small size is the point.  Also a trimmer on the board is used when you need to adjust the setting once and then leave it there without access for adjustment from outside the box.  

There is no absolute reason that this needs to be permanently adjustable.  You could temporarily wire in your pot, adjust to the desired set point and then measure the bias voltage or the two resistances between the wiper and the end lugs of the pot.  You could then use two fixed value resistors to set the voltage.  Changes in the bias voltage on the grid of the tube changes the gain of the tube.  SO, you would probably want to use the trimmer so that you can tweak the effect of the pedal.  You can also try different tubes that have different gains in the pedal to explore their effect.  Here's a link to a chart showing the gain of 12AX7 type tubes with some additional information.

http://thetubestore.com/gainfactor.html

The trimmer really is the way to go!

[Paul Marossy]

It's a 10K trimpot.

[mrfirstime]

Thanks ill give that a shot.