Individual Bias Power Tubes.

[KramerBassFan]

Hello Talkbass.

I recently built myself a Superbass, which i intended to both play on, and use as a learning experience.

One of my planned mods is.... a bias for each of the power tubes.

I would like this so i will have no real use in buying a matched set of tubes, and can experiment with different brands of power tubes, mixed and matched.

But thats not really the point.

My point is, HOW do i do this?

My Superbass already has one bias pot, which controls the EL34 Quartet.



P.S. I'm not worried about "hurting resale value" or "chopping up a nice amp" or anything like that. I built this amp in the first place to LEARN FROM.



Any help is appreciated.

Thanks, Ben

[KramerBassFan]

Anybody?

[UncleFluffy]

Can you point us to the schematic you used? That would make it easier to figure out what needs to change.

[KramerBassFan]

https://taweber.powweb.com/store/6m100_schem.jpg

Heres the Amp schematic,

and here is a bias diagram that was recommend to me...

[UncleFluffy]

My instinct - and this is something that would need reviewing by others - is that it would be fairly simple to set up a second bias pot for the second pair. Consider what follows a rough sketch that needs checking through with pencil and paper.

Duplicate the bias circuit from D1 through point H and set up the second pair of power tubes in the same way as the first. Instead of coupling them through F and G, add an extra pair of coupling capacitors alongside C1 and C2. Resistor and capacitor values will probably need changing to keep things balanced.

Adding a bias pot per tube would be a bit trickier, methinks, but I'm far from expert here.

edit: wasn't able to see the second diagram, forum wants me to register.

[KramerBassFan]

Oops, sorry about that....

I'll replace the link with a picture.

edit: done. And it looks somewhat like what you suggested.