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Operator’s Verdict: Buy the amps first, the brand second: a 100W HF radio (FT-891: 23A, IC-7300: 21A, per their specs) needs a 30A-class continuous supply — not an intermittent-peak “30A.” For most shacks a ham-grade switching supply like the Samlex SEC-1235M is the practical pick; a linear Astron remains the zero-noise gold standard if weight doesn’t matter. QRP operators can run almost anything clean.
Sizing: the Only Spec That’s Non-Negotiable
Your supply’s continuous current rating must exceed your radio’s maximum transmit draw with headroom — the same rule as field batteries, without the amp-hours. From manufacturer specs:
| Radio | Max TX draw | Supply floor |
|---|---|---|
| QRP (IC-705, X6100, G90) | 3–8 A | 10–15 A class |
| Icom IC-7300 (100 W) | 21 A | 30 A class |
| Yaesu FT-891 (100 W) | 23 A | 30 A class |
| 100 W radio + accessories | 23 A + | 30–35 A class |
Two traps hide in the ratings. First, some supplies advertise a peak (“surge”) figure and a lower continuous figure — SSB voice rides near peak long enough that the continuous number is the one that matters. Second, voltage sag: a supply that droops under key-down shows up as reduced power output and, on SSB, distorted audio. If your radio’s meter dips hard on transmit, suspect the supply before the radio.
Switching vs Linear: the Noise Question, Honestly
Switching supplies are light, compact, efficient, and — when designed for amateur use — quiet. Several ham-grade models include a noise offset control that shifts the switching frequency so any residual birdie moves off the frequency you’re working. The horror stories mostly come from generic industrial or LED-strip switchers, which can spray hash across the HF spectrum.
Linear supplies (the classic Astron RS series) solve the noise question by construction: a transformer, rectifier, and pass transistors produce no switching hash at all. The price is mass — a 35A linear is a shelf-bending purchase — and efficiency. They also last approximately forever, which is why used Astrons are the perennial hamfest bargain.
The honest decision rule: HF-focused shack in an apartment where every dB of noise floor counts → linear or a proven ham-grade switcher. Everything else → ham-grade switcher and enjoy the desk space.
Pro Tip: Chasing a noise problem? Before blaming the supply, check whether the bands themselves are the issue — current band conditions and the solar dashboard will tell you if today’s noise is geomagnetic rather than local. Field operators: the battery-side version of this sizing math lives in the POTA power budget calculator.
The Picks
Best all-round shack supply
Samlex SEC-1235M
A 30A ham-grade switching supply with a long track record in amateur service — the default recommendation for any 100W HF station, with metering on the M version.
- 30 A switching
- 13.8 V
- Compact
Ham-radio staple brand; pair with Powerpole distribution (guide).
Budget 30A with noise offset
TekPower TP30SWV
A 30A digital switching supply with adjustable voltage and a noise-offset control — the value route to powering a 100W radio.
- 30 A switching
- Adjustable V
- Noise offset
Verify the 13.8V setting with a meter before first connecting the radio.
The linear option: Astron’s RS-35M is the classic — heavy, silent on RF, and frequently outliving its owners. Availability on Amazon comes and goes; check current stock or watch the used market, where clean examples are common.
Frequently Asked Questions
What size power supply do I need for a 100W HF radio?
Size from the radio’s published maximum transmit draw plus headroom: an FT-891 specs 23A and an IC-7300 21A, so a 30A-class continuous supply is the correct floor for any 100W radio. A “30A” supply rated only for intermittent peaks is not the same thing — check the continuous rating.
Are switching power supplies too noisy for HF?
Modern switching supplies designed for amateur radio are generally quiet, and several include a noise-offset adjustment to move any residual birdie off a frequency you’re using. Generic switchers not built for radio use are the risk — they can put hash across HF. Linear supplies (like the classic Astron RS series) remain the zero-RF-noise option at the cost of weight.
Can I run my radio from a computer or LED power supply?
It’s a gamble that usually costs more than it saves: non-radio switchers often produce broadband RF noise right where you’re trying to listen, and many aren’t regulated to hold 13.8V at full transmit load. If a bargain supply is the budget, a used Astron linear is the safer bargain.
Do I need 13.8V exactly?
Most 12V amateur gear is specified for 13.8V ±15%, matching a vehicle’s charging voltage. Radios generally deliver full rated output at 13.8V and may reduce power as voltage drops — one reason a supply that sags under load shows up as low output and distorted audio reports.