I have a 120 VAC X 24 VAC, 50 VA transformer that I want to use for accessory power. Most of the accessories are 14 - 16 VAC. What size resistor would I need and how would I wire it?
Not much of an Electrician.
I’m picking up lumber & supplies in town to build a house. What size truck do I need? Not much of a carpenter.
Same answer - it depends on the load.
In your case, you really need a device to control the voltage, not the resistance. A resistor in the circuit you are considering is a current limiting device, not voltage limiting. With a very low current accessory, you could keep raising the resistance and not see any difference in voltage.
See the J&C Studios solution by Dale H. on how to do exactly what you want HERE. One of these easy-to-build arrays will provide a large number of voltage steps to choose the right one for each accessory.
He’s got a lot of the numbers wrong in that posting.
For example, half-wave voltage is 71%, not half, of the full-wave RMS voltage. Applying that to an incandescent lamp results in about 58% of the full-wave power and about 30% of the light.
And the anti-parallel diode scheme, which is a good idea that I have often advocated, will however drop only about .5 RMS volts per diode pair, even though the DC drop across a diode is about .65 volts. The AC drop is not constant along the string of diode pairs.