CCS biasing: Avoiding current in a potentiometer wiper

[Hearinspace]

I do that when I build a final amplifier. But I want to be able to change the current by a wide range when prototyping, without re-soldering.

Ita consentimus.

 

[6A3sUMMER]

Some of you readers/posters on Tubes/Valves,

One of my fellow engineers said something that was to this effect:
When something is engineered, the outcome needs to be predicted.
I always thought that was an interesting statement.

Failure takes place, when the outcome is not properly predicted.
The best example of that is the Original Tacoma Narrows Bridge.
Be sure to look it up, if you are not familiar with that failure.

 

[Mark Tillotson]

If the wiper loses contact, the gate is open in the right schematic - not a good situation.
in the left schematic, the gate is still connected to the resistor U4

But you can add a high value resistor (100k?) between gate and an appropriate point in the circuit to turn it off if the wiper opens. Here its a depletion device so I think it goes from gate to the bottom terminal of the pot in RH circuit. For enhancement FETs it simply goes gate-source.