Question: [![enter image description here](https://i.stack.imgur.com/UA06h.png)](https://i.stack.imgur.com/UA06h.png)

I have this circuit with both AC and DC supplies and am trying to calculate the voltage at Node A.

Is it possible to simplify the circuit somehow? 

**edit:**  

The voltage will fluctuate 3Vrms above and below the 12V DC. Does that mean that ideally, on the positive half wave, the Zener will cut the top off the sine wave at 5.1v.

Answer: 
> 
> I have this circuit with both AC and DC supplies and am trying to
>  calculate the voltage at Node A.
> 
> 
> 

[![enter image description here](https://i.stack.imgur.com/4l0MD.png)](https://i.stack.imgur.com/4l0MD.png)
Very fast answer:

Node A is 12V + 4.24Vp and 12V - 4.24Vp; max 16.24V min 7.76V.
The answer for Node B is 5.1V DC, since Node A minimum voltage did not goes below 5.1V.

To calculate the RMS value:
Vrms Node A = Square root(12 X 12 + 3 x 3) = 12.37V
[![12VDC + 3Vrms](https://i.stack.imgur.com/9qutw.png)](https://i.stack.imgur.com/9qutw.png)