Using a POT for a split plate load...

[Paul-in-KC]

All,

I would like to set up an adjustable split plate load.

Using a potentiometer for this seems ideal. One side to B+, the other to the plate, and the wiper to the coupling cap.

What I'm curious about is that I read somewhere that "...most POTS are not designed to be subjected to raw DC like this...".

The term "raw DC" strikes me as odd - but that's not my question.

My question is - if I have a POT that is rated for the power and voltage that will be present, is there any reason that a potentiometer should not be used to implement an adjustable split plate load?

Of course I would have the part spec exceed power and voltage by a significant margin.

Thanks,
-Paul

[gingertube]

There is no problem when it is a "Set and Forget" pot. If you try adjusting it while operating you will get "earth quakes" as you adjust the pot due to the changing DC level.
Cheers,
Ian

[husky]

All,

I would like to set up an adjustable split plate load.

Using a potentiometer for this seems ideal. One side to B+, the other to the plate, and the wiper to the coupling cap.

What I'm curious about is that I read somewhere that "...most POTS are not designed to be subjected to raw DC like this...".

The term "raw DC" strikes me as odd - but that's not my question.

My question is - if I have a POT that is rated for the power and voltage that will be present, is there any reason that a potentiometer should not be used to implement an adjustable split plate load?

Of course I would have the part spec exceed power and voltage by a significant margin.

Thanks,
-Paul

You might want to put a series limiting resistor in

[Paul-in-KC]

You might want to put a series limiting resistor in

Ah - the old split, split-load

Yes, I was thinking about that too. I think I'll play with it a bit without a limiting resistor, just to see what the smallest value that I might want to use on the B+ side.

Like with really hot humbuckers and 12AX7s in V1, V2, and PI.

Thanks for the suggestion!
-Paul

[husky]

You might want to put a series limiting resistor in

Ah - the old split, split-load

Yes, I was thinking about that too. I think I'll play with it a bit without a limiting resistor, just to see what the smallest value that I might want to use on the B+ side.

Like with really hot humbuckers and 12AX7s in V1, V2, and PI.

Thanks for the suggestion!
-Paul

If you don't use a limit resistor make sure you measure the voltage across it, do ohms law and remember that the AC voltage (signal) matters as well.

[tictac]

Voltage rating could be a problem, you'll end up introducing noise to the circuit if your pot isn't rated for at least 500VDC. Even then a pot really is not the ideal component for this application. If it's a set it and forget item, why not get some resistors of the proper voltage rating and try different values until you get the effect you like?

Ken Fisher used an 82k/22k combo; if you believe that he knew what he was doing you could start there...

just a thought...

TT

[Paul-in-KC]

Voltage rating could be a problem, you'll end up introducing noise to the circuit if your pot isn't rated for at least 500VDC. Even then a pot really is not the ideal component for this application. If it's a set it and forget item, why not get some resistors of the proper voltage rating and try different values until you get the effect you like?

Ken Fisher used an 82k/22k combo; if you believe that he knew what he was doing you could start there...

just a thought...

TT

Well - I'd say it is sort of a "set-and-forget", but something that I might still want to adjust based on tubes, pickups, target sounds.

Interesting that KF used an 80/20 split. That happens to be the split that I like with my Les Paul. I still have very tame tubes installed, but with the tame tubes and semi-hot pickups, I really like the 80/20 split a lot.

It will take me some time to swap tubes and use different guitars and see if I think this needs to be adjustable. Perhaps I'll conclude that the 80/20 split is good for everything.

Very cool to hear that KF used that split too. I had never heard that he did. Though, it makes sense - since he did tweak amps for particular player tastes.

As always, many thanks for the input.

-Paul