Author: N4GA – Rob
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January 2019 LDMOS Amplifier
Here’s my latest dual 1K80H amplifier, mostly in pictures. Actually, this is not “my” design. I built this in an afternoon and it most resembles the Elecraft amplifier from the drains back (output section). The Elecraft output section design looked pretty elegant and simple. So I wanted to try and copy it and see how…
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Single versus Dual Bias for LDMOS RF Amps
Last year I decided I would design and build a regulated temperature-compensated independently adjustable dual bias circuit for my 2x LDMOS amp. (what a mouthful) Why? Because I wanted to try an experiment which actually works in a class AB audio amp. This being the ability to adjust the bias to affect the mix and…
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Biasing Schemes Revisited
So I’ve gone around the block on this one. Tried a bunch of designs, studied a bunch of others and finally designed my own! The goals of the bias circuit include: #4 is the key. As a LDMOS heats up, Ids will rise and the gain changes, causing the LDMOS to drift into a less…
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Transmission Line Transformer Testing
Jerry Sevick, W2FMI (SK) called this the “Soak Test.” He used it to run real power through the TLT network to check efficiency. It’s a pretty simple test whereby you simply run significant power through the TLTs and measure the temperature rise in the cores. If they get hot, they are not as efficient as…
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Nulling the Even Harmonics
There’s a quite famous audio amplifier builder (legendary really) named Nelson Pass that makes very high end audio amplifiers. In some of his amps, he even goes so far as to allow you to manually skew the bias via a knob on the front, so you can slant the harmonic content towards even or odd…