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I recently purchased a MiniPA 100-watt HF amplifier kit. It is a class AB push-pull amplifier and uses the MRF 9120 transistor. While doing some reading on this amplifier kit I noticed some discussion of using a pair of the more powerful MRF300 transistors, which could theoretically increase the power output to 600 watts.

My question is whether one could actually replace the MRF 9120 with a pair of MRF300s in this kit, and if so, how? Would the changes be doable by an inexperienced kit builder or would they be more complex?

In general, when thinking about building/modifying amplifiers, how can I reason about component-swapping - what are the most important things to check?

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  • $\begingroup$ Welcome to ham.SE! :-) It's good that you asked that before trying it. $\endgroup$
    – Mike Waters
    Commented Aug 11, 2023 at 23:47

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I didn't look up the differences between the two transistors; but the main question I have is, Will that heatsink dissipate 600 watts?

It's not likely that the stock heatsink in a 100 watt amplifier will, thus you risk destroying the bigger transistors.

After looking at the photos, what about the transformers and other components? Looks pretty risky, IMO.

I think your best bet is to spend the money on a higher and/or higher-gain antenna. You'll hear better too.

In general, when thinking about building/modifying amplifiers, how can I reason about component-swapping - what are the most important things to check?

Well, there's really not a simple answer for that. If you would have asked that as a standalone question, it probably would have been marked as Too Broad, because there are countless different amplifier circuits, and often a lot of fine details. Sorry. :)

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