Might want to read up.

If emitter followers are driving a load with a capacitive component, it
is reflected
to the input as a negative resistance. You can prove this with only
the simplest
hybrid pi model. It's a parasitic oscillation, not a loop oscillation
which couldn't
happen with gain 1 as you point out. You add enough series base
resistance
to swamp out the negative resistance, making it stable. There is
enough capacitance
in the wiring to excite the phenomena. This is why you see resistors
in the base
circuits of emitter followers all the time.

Darlingtons are much worse. You can show that with the hybird pi model
as well.
The oscillation will be near fT. That's a few mhz for 3055 type
devices.

Bulbs usually burn out open, true. What about some other short? The
circuit has NO short current protection other than the beta of the
transisitor. The base current becomes 1/beta of whatever short circuit
current flows. If the pot is set very near the max end of it's range,
dissapation will destroy the upper part of the resulting divider stick.

I have replaced enough of the panel mount edge adjust pots in Bonanzas
which have
this exact setup to know. Know what those cost?

The P-fet works great because you can get the output clear to the rail,
not the rail - 1 diode drop
as you are limited to with the 3055 approach or 2 drops in the
darlington approach.
It's inherently current limited by IDss as well. Draw it out: The
source goes to +14,
the drain to the lamps to ground. The control pot goes with the hot
end to +14, the
wiper to the gate, and the other end to the bulbs. So it also has a
small amount
of loop gain-- makes the adjustment very smooth. The huge gate-drain
capacitance
of the v-fet structure miller multiplied by the gain of the FET ensures
stability under
all conditions.

Maybe you should write it up for kit planes.

I won't be applying to RST anytime soon, but I did think you were
better than this.

Bill Hale