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Hi!
I am being a bit frank here and is actually asking you skilled guys why my JFET Power Amplifier oscillates.
I don'r know if Ti manufactures BF245A but I hope so otherwise it is a slim chance of getting help :)
BF245A is my favorite JFET and I have built a "copy" of the famous Williamson Tube Amplifier from 1947 using BF245As.
As "Power tubes" I am using 2SK175 right now but have found more linear versions which I will use in the future, the 2SK135.
I have kind of come to the conclusion that the warm tube-sound isn't actually because of the tubes, it seems to be because of the output transformer which shortens out even harmonics.
So I have built a JFET pre-amp with MOS output transistors in a push-pull arrangement around a transformer which I have wounded and glued manually using laser-cut FR2 and a transformer core made by the best C-Core transformer manufacturer in the world, Lundahl Transformers.
The first use of my amplifier is intended to be as a guitar amplifier which my current data actyually shows work fine.
However, I have hopes for more.
Right now I have a FULL POWER bandwith of only 20Hz-5kHz, here I get 8W output.
But at 20kHz I only get 1W output before the signal turns realy weird, it almost looks like a frequency doubler!
I have measured the signal at MOS gate and simuoltanoulsly at MOS drain but at 20kHz they do not look the least a like which makes me understand nothing.
I am attaching some pictures of this and more.
I really hope you may want to help me even thou this really is not related to any of you fine products.
Kind of desperate as you can see :)
Best regards, Roger
PS
High output current AND say 1kHz works, high output current AND 20kHz does not work (please see AND as a logical operator).
Open Loop, 1kHz, Upper: 0,5V/DIV (Input), Lower: 5V/DIV (Output), Z=3,9 Ohm
Closed Loop (BF=12dB), 1kHz, Upper: 0,5V (Input), Lower: 5V (Output), Z=3,9 Ohm
20kHz, Open Loop, Upper: Ug at Power_MOS (sensitivity=unknown but not important because signal is "good"), Lower: Ud at Power MOS (sensitivity probably 5V/DIV), frequency is doubled :)
