# Novice Help AC DC Loadlines 6J5

Discussion in 'Electronic Basics' started by GP53, Dec 1, 2004.

1. ### GP53Guest

Howdy,

6J5 Triode Circuit

I'm looking for some help. Why when I use an AC plate
supply(250VAC/RMS), are the voltage values in the circuit different than
when I use a DC plate supply(250VDC) in the same circuit. The grid
supply is -4VDC and I've got a 25K sense resistor in series to the
plate(10ma of current). All the numbers using DC calculate out just
fine. When I use an AC supply, voltages are different. TIA.

GP53

3. ### Tim WilliamsGuest

I'm with John, what's the AC about eh?
It'll be at least half due to the plate half-wave rectifying the input.
Depending on the circuit (and how you measure it) it may be anywhere from
peak value, to a nonlinear middle point, or negative. (The nonlinearity
being how the tube responds according to a 3/2 power law, as opposed to
assuming the tube is a constant resistance = Rp while forward biased.)

Tim

4. ### GP53Guest

John,

In order to curve trace this circuit on a scope, an AC supply is used as
a sweeping voltage. One leg of 250VAC secondary to anode, and the other
though the sense resistor, then to the cathode.

Alan

5. ### John FieldsGuest

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