If you've been asking how to build a CB linear amplifier, here's the honest answer: it's less about one magic circuit and more about wiring five or six well-understood blocks together so they behave. Get the blocks right and the amp works. Rush one of them and you get a hot, splattery, self-destructing box that takes out your final transistors on the first key-up. This is a builder's roadmap — what a CB/ham linear actually is, the core blocks, the device choices, what power you can realistically target, and the skills and tools you need before you fire it up.

What a CB linear amplifier actually is

A linear amplifier takes the RF output from your radio and boosts it while (ideally) preserving the shape of the signal — so SSB stays clean and AM stays undistorted. "Linear" is the key word. A well-behaved linear reproduces your input signal at a higher power; a poorly biased or overdriven one clips and generates splatter that lands on your neighbors' channels. On the 11-meter CB band and the nearby 10-meter ham band, that means an RF power stage designed to stay linear across the voice envelope, not just make numbers on a meter.

Everything else in the box exists to support that one stage: feed it clean DC, switch it in and out on transmit, filter its output, and keep it from oscillating.

How to build a CB linear amplifier: the core blocks

Really, the whole project comes down to these blocks and how they hand off to each other:

  1. RF deck (the amplifier stage). One or more RF power transistors configured as a push-pull pair or paralleled devices. This is the heart of the amp and where your device choice lives.
  2. Input matching / splitter. A small transformer network that presents the right load to your radio and, in push-pull designs, splits drive between the two devices with correct phase.
  3. Output combiner / transformer. Combines the device outputs and transforms the low transistor impedance up toward 50 ohms. Broadband ferrite transformers are the common approach in CB-class solid-state decks.
  4. Low-pass filter (LPF). Non-negotiable. Solid-state amps generate harmonics, and a proper LPF after the deck keeps that garbage out of the antenna. Skip this and you're transmitting on frequencies you have no business being on.
  5. Bias network. Sets the transistors' idle current so the stage runs in a linear class (commonly a Class-AB scheme). Bias is what separates a clean linear from a splatter box.
  6. T/R switching. Routes RF to the amp on transmit and bypasses it on receive, and keys the amp in step with your radio — usually via RF-sensing or a PTT line.
  7. Power supply. The unglamorous block that decides whether any of the above works. More on this below.
Build tip: Get each block working on its own before you chain them. Bench-test the power supply under load, verify the LPF sweeps clean, confirm T/R switches cleanly — then integrate. Debugging a fully-assembled amp that "just doesn't work" is miserable; debugging one block is easy.

Device choices: pill amps vs LDMOS

Two families dominate the conversation, and they pull in different directions.

Bipolar "pill" transistors (BJTs). The classic CB linear path. Devices like the Toshiba 2SC2879 are common CB/ham RF power BJTs, each rated in the neighborhood of 100W of RF output per device as a general figure — always confirm against the current datasheet for the exact part you buy, and treat any single number as nominal. Builders parallel or push-pull these to reach higher totals. Pills are proven, forgiving to drive, and there's a deep well of reference designs. The catch: the market is full of counterfeit and re-marked pills, so source carefully and expect real parts to cost real money.

LDMOS (laterally-diffused MOSFET). The modern RF power path, widely used in newer ham amplifier designs. LDMOS devices tend to offer high gain and good ruggedness against load mismatch, and a single modern device can be built for substantial output. They typically want a higher, well-regulated supply voltage and careful bias and thermal design. For a first build, LDMOS is absolutely doable but less forgiving of sloppy layout than a basic pill deck.

Which to start with? If this is your first RF power project, a modest pill-based push-pull deck with a solid LPF teaches you every fundamental with the most available reference material. Move to LDMOS once you're comfortable with matching, bias, and thermal management.

Realistic power expectations

Here's where the facts-only discipline matters most, because power numbers get wildly exaggerated online. Output depends on your supply voltage, drive level, device count, matching efficiency, and tuning — it is not a fixed property of "the circuit."

As a design target, a single-pair pill deck is commonly built for roughly a few hundred watts PEP, and larger multi-device or LDMOS decks are built for more — but the honest number for your amp is the one you measure on a calibrated meter into a dummy load, at your actual supply voltage and drive. Use the datasheet rating of your specific device and your build's stated spec as the ceiling, and don't design to run a transistor flat-out at its absolute maximum. Headroom is what keeps finals alive.

Want to sanity-check impedance transforms, filter values, or transformer ratios before you cut ferrite? Our free calculators handle the math so you're working from numbers, not vibes.

Safety — read this before you build. RF power amplifiers combine several real hazards. High-current DC supplies can deliver dangerous energy and start fires through a shorted lead. RF at these power levels causes deep, slow-healing RF burns — never touch the output side while transmitting, and never run an amp without a proper load (dummy load or matched antenna). LDMOS-class supplies and mains wiring carry lethal voltages. If you're not confident working with mains AC and high-current DC, get someone who is. And on the legal side: know the power and licensing rules that apply to your band and country before you key up — that's on you, not the schematic.

The power supply is half the build

New builders obsess over the transistor and treat the supply as an afterthought. It's the reverse. A linear stage can only deliver clean peaks if the supply holds voltage under the sudden current draw of a voice peak. Sag on peaks equals flat-topping equals splatter. Whatever deck you build, the supply needs to hold its rated voltage under the amp's peak current with margin to spare, with low ripple and generous bulk capacitance. Size it for the peaks, not the average.

T/R switching and staying on the air cleanly

The transmit/receive system does two jobs: route RF correctly in each state, and key the amp in sync with your radio. RF-sensing (VOX-style) switching keys the amp when it detects drive, which is convenient but adds a tiny delay and can clip the first syllable if it's slow. A hard-keyed PTT line is cleaner and more deterministic. Relays or PIN-diode switching handle the RF routing. Whatever you choose, the amp must be fully switched before RF hits it — hot-switching relays is a classic way to weld contacts and destroy finals.

Skills and tools you'll actually need

You don't need a pro RF lab, but a few things separate a working build from a smoking one:

  • Soldering that can handle heat — RF power grounds and ferrite transformers need a real iron, not a hobby pencil.
  • A dummy load rated for your target power. Non-negotiable for testing.
  • An SWR/power meter to measure real output and watch for reflected power.
  • A DC supply and a multimeter to set and verify bias current before you ever apply drive.
  • Heatsinking and thermal paste sized to the dissipation — RF power transistors die from heat faster than anything else.
  • An oscilloscope (nice-to-have) to actually see flat-topping and confirm you're staying linear.

Where the build guides come in

The blocks above are the map. The hard part is the specifics — the exact transformer turns, the filter component values, the bias-setting procedure, the layout that doesn't oscillate. That's what separates a week of frustration from a clean first-key-up. Our step-by-step guides lay each block out with the values and procedures worked out, so you're building a proven design instead of reverse-engineering fragments. Browse the volumes to find the deck that matches your target, or start with the full catalog if you're still deciding between a pill build and LDMOS.

Build one block at a time, measure everything, respect the supply and the safety rules, and a CB linear amplifier is a genuinely achievable project. Cut corners on the LPF, the bias, or the switching, and the amp will tell you — usually with smoke. Do it right the first time.

Build it right — with the full documentation

Want the shortcut instead of reverse-engineering a dozen dead forum threads? Our Master Bundle — 90 complete builds, $34.99 gives you full RF decks, filter values, bias schemes, and T/R wiring laid out block by block so you can build with confidence instead of guessing. It's the same bench-tested roadmap this article outlines, expanded into ready-to-follow guides.

Browse the Build Guides Free Calculators

Get the free Builder's Quick Reference

Bias cheatsheet, transistor substitution tables, and the 10 mistakes that kill amplifiers. Free — no spam.

Educational reference only. Always follow your specific device datasheet and build documentation, and verify all values independently. Working on high-voltage and RF equipment carries real risk — if you're unsure, get help from an experienced builder.

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