For the network of Fig. 33, if $C=1 \mu \mathrm{F}$, find the level of $R$ that will result in a $50 \%$ conduction period for the load in either direction if the turn-on voltage for the diac in either direction is $12 \mathrm{~V}$ and the applied sinusoidal signal has a peak value of $170 \mathrm{~V}(=1.414 \times 120 \mathrm{~V})$ at $60 \mathrm{~Hz}$