Just because I have a POS TENMA on the bench at work that FAILS this bit....
The Voltmeter needs to read output voltage setpoint when the output switch is turned off, NOT READ ZERO when the output is off. How useless is that? For bonus points make the current meter read current limit setpoint when the output is off.
I successfully built a valve based radio transmitter within the 9V battery limitation at school, I Just used 100 9V Nicad packs in series for B+. The teacher never clocked what I was doing, turns out that 900V DC @ 100mA is quite sufficient to talk around the world on 20M CW, also turns out that 9V battery snaps are **not** rated to break 900V DC under load, and neither are small glass fuses....
Regards, Dan.