Re: LTSpice simulation of uBitx Power Amp

Diver Martin <diver.martin@...>

Looking at the schematic, has anyone tried changing the turns ratio on T10, or monkeying with the preamp?  It would lower the drive level, but also lower the drive impedance.  One might also increase the resistance slightly of R90/93 (increasing the drive bias of the preamp stage, dangerous) or lowering the emitter degeneration resistors (R941, 911, 942 and 96) from 22 ohms to something like 10 ohms (Degeneration is useful here though, it provides linearity to the amplifier).

I use IRF530's in a different amplifier design that puts out 50W with about 3W in at 30MHz.  Not sure what the preamp stage is rated for, I'd assume ~0.5 to 1W tops.

On Mon, Feb 5, 2018 at 11:29 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
I suppose.
The LTSpice model of the IRF510 does assume worst case, perhaps that is part of it.
But the WA2EBY model is off from the performance reported in the QST article by more than I would expect when operating at 30mhz.
And the uBitx models pretty close to the performance we actually get.

Regardless, looks like we'd do well to hack the uBitx to use something closer to the WA2EBY circuit.
And if that doesn't give the required performance at 30mhz, then drive the IRF510's from a lower impedance source.
LTSpice is whispering to me that if driven hard enough, the IRF510's will do 30W at 30mhz.

Jerry, KE7ER

On Mon, Feb 5, 2018 at 10:47 am, Diver Martin wrote:
> Let me know if anybody figures out why my model of the WA2EBY amp shows the output to be so much lower at 30mhz
To quote George E.P. Box, "All models are wrong, but some are useful."
Spice models are just that, models.  They're rarely right.  But they can tell you useful things about some of the mechanics of what's going on inside the system.

Martin Held - AE7EU
If there aren't any questions, then what is there to learn?

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