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On Mon, 21 Jun 2004, david.g3ryp wrote:

I've taken the measurements you suggested and indeed it was the driver whose output was low - only about 1 volt peak. I was using BC549s throughout and although they tested ok when I changed them in the pre-driver and driver stages for 2n2369s the output from the driver went up to 4.5volts peak.

I've tried a variety of core types and none appears to be critical. I'm using a t-50-6 in the IRF510 drain - 14 bifiliar turns to get the 3uh you suggest. Know what you mean about winding these things!

The output without the lpf in circuit is 6.25watts but I need to adjust the bias for a standing current of rather more than 80ma to achieve this - although it may be that the balanced mod is not that well balanced (I haven't put in any caps yet).
I'll test this and let you know. Even without the lpf the output is quite a pretty sine-wave.

Now where does this 6.3 volt resistor fit in? Am I looking at the wrong schematic? Perhaps in the driver emitters? I'll try changing the 10 ohms to 5.6 or thereabouts and see if the output goes up.

The driver and prediver's emitter resistors are 6.2ohms (i used 5 ohms).

due to the feedback design, individual transistor types are non-critical.
the driver did require a heavier than BC147/2N3904 type of transistor.
The plastic package prevents one from being able to gauge their heating by
just touching them. until they are properly cooked.

the 2N3866 will do fine. the latest 'build' of the circuit is on
www.phonestack.com/farhan.

- farhan

Lastly thanks for putting a unit on the rf voltages. All too often schematics either don't contain rf voltages at all or they don't specify whether they're Peak to Peak or Peak or RMS - and there's quite a difference!

I think I'll change the other 549s for 2n2369s if I have enough just to see what happens.

Good luck to everyone.

David