Simple circuit. Layout easy to follow. No biasing or other adjustments necessary. Should be able to complete without the assistance of a technician. The usual precautions apply with respect to working with high voltages. A very good beginner project.
Moderately complex. Interactive and cross connected stages require concentration on wire routing and placement to ensure minimum noise in the signal. Difficult to build in one sitting. Best to use flags and markers to assist in resuming the build.
Complex circuit. Circuitry that is more dense and more difficult to follow the layout and schematic. Requires much concentration and rechecking to ensure everything is according to print. If the circuit has adjustable bias, you will need the assistance of a qualified technician to assist you setting up the amp for proper operation.
Very Complex. Many stages that are interactive, multiple power supply filter poles, many tone and volume controls, effects, dense circuitry that is prone to noise and distortions if the wiring is not routed properly. Suggest the builder enlist the assistance of a veteran kitbuilder or electronics technician.
Extremely Complex. All of the issues of levels 1 through 4. Probably best to be built by a veteran kitbuilder or electronics technician who possesses the proper tools for building and troubleshooting electronics circuits and systems.