24-07-2017, 08:20 PM
(24-07-2017, 04:06 PM)Nowhere-Man Wrote: Class A stage was the one that had me most baffled. Rules so far are, the output waveform should be in phase with the input.
No! That is impossible!
As the input signal becomes more positive, the anode current increases which causes a corresponding increase in the voltage drop across the load. Thus the anode voltage drops i.e.: goes negative.
Thus input and output voltages are in anti-phase.
You are obviously still confused by the concept of grid current. The whole point is that grid current should never be allowed to flow in virtually all applications. The leaky grid detector is an obvious exception but the current in that case would be infinitesimally small.
As for the grid always being negative wrt the chassis, that is rarely the case with indirectly heated valves. If you look at the 5-10 circuit again, you will see that the grids of the EF86 and EL84s are connected to the chassis (via a resistor) but there is a resistor in the cathode circuit which develops a positive voltage on the cathode wrt the chassis. The grids are, therefore, negative wrt the cathodes.
