LF: Output transformer problems

[G0MRF@aol.com]

In a message dated 5/11/04 10:59:45 PM GMT Daylight Time, vernall@xtra.co.nz writes:

> >well I rewound the ouput transformer.
> >Again I have problems, and when checking the signal on
> >a spectrum analyzer I found that it is peaking on the second harmonic.
> >So it transmits the main signal on 272kHz.........
> >136kHz is also present at the ouput, but much much weaker.
> >
> >It really makes me puzzling.
>
> Double trouble.  Are you certain of the windings being correctly phased for
> "push-pull"?  You may have made a "push-push doubler"???
>
> 73, Bob


Hi.

Have been following this topic.  Maybe this will help.
 
I've just wound 10 turns on a 58mm 3C90 core and the inductance measured 353uH. 

The 10nF on the drains are intended for spike suppression not resonance.

If you can change the design to get class E, at your required output power, then efficiency / dissipation / drain transients would all improve.

The square wave drive should not contain significant amounts of second harmonic.  The "push pull doubler" can be created by a fault in the FETs insulating washers, or if they are directly connected to a common isolated heatsink.

Do you have square waves on the drive?  Upside down Schottky diodes will distort the drive and cause excess dissipation as the FETs will not be fully 'on'

Good luck

David  G0MRF