Mains AC is 110V RMS
Transformer's output is 6.3Vac RMS
Peak transformer output is 6.3*√2=8.9V
1N914 Diode drop @3.35mA ≃ 0.75V
Vmax on load = 7.36V (8.9-2*0.75)
Worst case ripple: Vr=(I*dt)/C
I = output current (U/R = 7.4/2200 = 3.4mA)
dt=capacitor discharge time (1/120ms)
C=capacitor value (15uF)
Calculated ripple: 1.87V
"Measured" ripple: 1.29V
