Dual Bias on Poseidon

[JW34]

Are the Output tubes on the poseidon biased together or independently? Has anyone ever set the board up for seperate bias?
How is it done?

Thanks,

Jay

[JW34]

I"m sorry, I shoulld be a little clearer.

For the Mark III, can you bias each individual KT-88 using the Poseidon baord or is it built into the board already. I see that there is only one bias pot so I am guessing that it is an overall ballance between the KT88's. I would like to bias each KT88 individualy.

I don't know a lot about this so I am trying. If any of this sounds like jiberish it is due to my lack of experience. Any help is greatly appreciated.

Thanks,

Jay

[Brik]

...
For the Mark III, can you bias each individual KT-88 using the Poseidon board or is it built into the board already. I see that there is only one bias pot so I am guessing that it is an overall balance between the KT88's. I would like to bias each KT88 individually.
...

Hi Jay,

It's been a while since I worked on a Mark III.
I think the original Mark III came with a matching pair of KT88s/6550s and the bias adjustment was done for both valves with a 10K pot that is located on the chassis.


You are correct that the balance between the valves is adjusted through the pot on the Poseidon board.

/b

[Rex Everything]

IIRC with the Posiedon board you use the pot on the board and the original bias pot on the Mark III to set bias for each tube

[JW34]

IIRC with the Posiedon board you use the pot on the board and the original bias pot on the Mark III to set bias for each tube

Well, I know that the 10K pot and the pot on the board are used to bias both outputs, but what I would like to know is, can I use two 10K pots outside the board along with the pot on the board to bias each KT88 or 6550 seperately.

Any ideas?

[Brik]

Well, I know that the 10K pot and the pot on the board are used to bias both outputs, but what I would like to know is, can I use two 10K pots outside the board along with the pot on the board to bias each KT88 or 6550 seperately.

Any ideas?

The Poseidon's method of using one pot for the bias level and another for the balance will let the user to set the bias for each of the output valves easily and quickly. I am not sure what you are trying to accomplish by changing the scheme. Remember the object of the bias adjustment is to, first, set the proper level of current through the valves, and second, balance the currents. That's exactly what the Poseidon's pots are designed to do.

Having said that, if you want to have individual control over each valve's bias, you can duplicate the encircled topology for each of the output valves.


Make sure to cut the connection between the two 100K resistors.
/b

[JW34]

I was under the impression that having individual control of each valves bias setup would make a difference in performance. I guess I am wrong here?

Jay

[TomMcNally]

Jay -

The scheme the Poseidon board uses is easier and
better than two controls. You set the bias in the
ballpark with the main control, then balance the
two tubes with the trimmer, touching up the main
control if needed. It's the same thing as having
individual controls, just easier and better.

There is no further improvement possible.

A perfect balance is good.

... tom

[JW34]

Cool. You guys rock. Thanks for the help one this guys. I WILL have more questions coming. I can't wait for my stuff to get back from powdercoating. I've been without my tube amps for over a year now and need to get away from SS. I am an electrician but not a electronic engineer. So I get some things but DC and electronics is a different monster.

Thanks again

Jay

[justinsweber]

I never used the pot on the driver board. I am using Triodes kit and DIYbaord... Im able to get the bais just right... 1.36- 1.4v Tirodes kit ties both together... single test point.

If I wanted to reset the bias... whats the order/sequence?

Thank you.

Justin