Solid State Tesla Coil Circuit

An advantage of the primary feed method is that it provides the necessary voltage transformation required to match the output impedance of the inverter to the resonator. This negates the need to employ a separate high frequency matching transformer or the use of elevated supply rails to get the required drive voltage.

A significant disadvantage of the primary feed method is that very tight coupling is required (k>0.35) in order to get good power transfer. This makes insulating the primary from the secondary somewhat challenging as the power level is increased.
The drive electronics is based around the TL494 PWM controller IC made by Texas Instruments. This IC is fairly "long in the tooth" but it is well behaved and is also easy to obtain. The IC contains an internal sawtooth generator and the necessary comparators and latches to produce the drive signals required for each MOSFET in the half bridge. The IC generates two complementary drive signals with a short dead time between transitions to ensure that one MOSFET has had time to turn off before the opposing device is turned on. Without this precaution the conduction times of both devices can overlap shorting the mains supply with interesting (read expensive,) consequences.
Full wave rectification,
This was achieved by using a full wave bridge rectifier between the mains line and the MOSFET bridge. This ensures that there is current flowing through the inverter during the entire supply cycle. The power drawn from the mains line roughly doubled as expected and the RF envelope assumed the classic full-wave rectified shape. This implies a considerable increase in the average RF energy applied to the TC.

Spark appearance:

Sparks became noticeably fatter and more bushy, but there was no increase in length. The picture opposite clearly shows the greater "fullness" of the discharge including wispy branches leading off from the main feature.

The tone of the sound changed to twice the pitch (100Hz) and became distinctly more "full-throated" and hissy.
Power is estimated to be around 300 watts.
These two pictures show the ability of the coil to produce a lot of corona from points. Notice how the discharge often divides into two jets of corona right at the breakout points.

Average RF power

Unlike a conventional damped-wave Tesla Coil, the solid state Tesla coil is capable of producing considerable amounts of sustained RF power. This leads to a few unusual things:

Firstly, the base of the secondary became very hot due to the high RMS current flowing through the fine wire. Maybe skin effect plays some part in this also. This is particularly noticeable if the system is run in CW mode for any length of time.
There is visibly more current in ground strikes than found with my spark gap TC.

Sparks to ground appear like pale ghostly white flames and arch upwards with the heat like the arc from a Jacobs Ladder. Anything flammable catches fire instantly in the arc.
I noticed that I got tiny RF burns if I touched anything metallic in the vicinity of the running coil even at fairly low power levels.

At one time I forgot to put the breakout point on the solid state coil, and an unused resonator about 2 feet from the solid state coil, (but quite close to me,) sprang to life with a firey crown of corona. Boy did that surprise me !!!