Low Voltage on Mosfets

gary350 said:

It will be interesting to see what happens when I replace the LC coil with copper tubing that will reduce skin effect 5 times.

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At your frequency litz wire is better than tube. If you make yourself litz wire from enameled transformer wire of about 0.5 mm it will be ok.
Most tubes you can get are made of low purity copper and they posses high resistance.

gary350 said:

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The most amazing thing is, the Mosfets don't get Hot like they use to. Mosfets use to get 50 degrees F hotter in 45 seconds, now they only get 7 degrees F hotter in 45 seconds and I am pulling 3 times more current than before. Maximum current use to be 8.8 amps now I am close to 35 amps but I am using different mosfets with much lower resistance.

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When the voltage dropped enough ( lowest point below about 14V ), the 7812 output also dropped and the Mosfets did not get enough gate voltage to turn them fully on.
It might be a good idea to have a separate rectifier + capacitor for the 7812, connected directly to transformer output, not to the main rectifier output.

jjw said:

When the voltage dropped enough ( lowest point below about 14V ), the 7812 output also dropped and the Mosfets did not get enough gate voltage to turn them fully on.
It might be a good idea to have a separate rectifier + capacitor for the 7812, connected directly to transformer output, not to the main rectifier output.

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I have always wondered how to know if the mosfets are turning fully ON and turning fully OFF?

It might also be good to have a different transformer just for 12 volts DC to the gates. I experemented a month ago with 8 AA batteries to provide 12 volts DC to the gates. It worked but not any better than what I already had at that time. Data sheet says 7812 is 1 amp at 12 volts. My meter say 8 AA batteies are 2 amps at 12 volts. I might need to experement with this again to see what I learn. The reason a tube amplifier has the audio transformer seperate from the power supply transformer is to keep the audio from modulating the power supply. Maybe in the past the 12 vdc voltage to the gates was being modulated by the fluxuating power supply voltage to the mosfets. Now that the power supply has a 35,000. uf capacitors the circuit is working way better than before. Maybe this is the answer to why the mosfets are now running much cooler than they ever did in the past.