question about measuring currents with the ammeter symbol . If I insert it, then the sim runs with no errors, but after there is no data to plot. removing the ammeter, the circuit works as intended. Any ideas why?

I think you need to

plot i(Vmeas)

. Doing a

plot signal

means

plot v(signal)

.

nothing can be plotted, all vectors are now "no such vector"

@Matt Venn edit the ammeter(s) and set or change the attrbute savecurrent to false:

savecurrent=false

This is due to a strange behavior of ngspice. If you dont save anything the default is used, that is save all voltage nodes and all voltage source currents (including ammeters, 0V sources). But if one ammeter is inserted with savecurrent=true it will add a .save i(vammeter) into the netlist to ask ngspice to save its current. When this happens ngspice takes the action and saves only the ammeter current. Another possibility is to add

save all

into the control block before the simulation (tran, dc, ac) line

thanks! that was it!