universal buffer/modulator

[julesison]

hi, and of course my first line has to be to apologise for my ignorance and secondly the possibility that this has been covered somewhere i couldn't find it.
i need to have a signal generator drive any number of different hf diy transformers that i want to experiment with. so i don't know what impedance the cct has to match only that the frequency will be from 20khz to 100khz max. is there not a "universal" impedance matching, "buffer" type device?
i attach a rough pic of what seems to me the perfect "cct". it would be basically a cct that allowed a signal generator to "modulate" the dc from a bench top power supply. for the sake of convenience it wouldn't have to swing + and -, it could be a square or sine all above zero. the power supply can be the current limiter through it's current output adjustment. i just need something that shows a high impedance to the sig gen output and that doesn't care about what's connected to it's output as it's current limited via the power supply anyway. surely this is the easiest way to be able to test "any" winding/transformer? sorry again if my simplistic approach is off but logically it seems sound?

[David]

The easiest way I think (and have seen done in commercial circuits) is to make use of the fact that the collector of a transistor is inherently a high impedance device when used as a current source. In essence, you need to put a pnp transistor between the output of the PSU and the coil (btw, I assume that you are going to find where the coil is resonant) via an emitter resistor, and bias the transistor to pass a certain current. Connect the Sig gen via a capacitor to the base, and the collector to the top of the coil.

Experimentation will be needed, and make sure the sig gen is set at full output. With outputs in the low RF area you might have to select the transistor carefully - high Hfe and FT are desirable.