The first frequency doubler simulation was based on a
JFET that has a single source, namely Linear Systems.
I have nothing against Linear Systems but most people I know, would rather use common off the shelf,
parts that are easy to obtain. This makes sense for future maintenence as well.
Well, Dr. Bruce Griffiths was thinking along the same lines and, as usual, put together a very nice design
using 2N3904 transistors.
I think most of us have these parts in our spare parts box. The two transformers would be Mini Circuits
parts with similar chracteristics.
Here is the schematic and the analysis: