Developer Reyes Amplifonics has recreated the Harmony H303 tube amp with three new plugins (two of which are freebies).
Reyes Amplifonics’ three new plugins include Triode, Reyes 303, and Kill Filter.
Triode is a paid plugin, costing $39.99, while the other two are free to download.
Before we get into the plugins, let’s take a look at where it all begins, with the Harmony H303 tube amplifier.
It’s no exaggeration to say that Reyes Amplifonics has crafted these plugins from the ground up, as the developer actually rebuilt a 1959 Harmony H303 tube amp.
The part-for-part rebuild includes point-to-point wiring, vintage tubes (new old stock), and a 6” Jensen Alnico speaker. If you’re interested in the process, the build is documented on the Reyes Amplifonics Instagram page.
The developer then component-modeled the build to create three new plugins.
All three plugins feature the original DSP from the H303 component model in some way.
Let’s start with the two freebies.
Reyes 303 offers the raw amp circuit with one-knob functionality. This plugin is built around a 12SQ7 triode preamp and 50L6 pentode output stage; two of the three tubes found in new old stock for the H303 rebuild.
Although these tubes have a common connection to 1950s radio, they offer something a little different from the typical vintage amp model.
One of the highlights of the Reyes 303 plugin is its dynamic tube saturation, which responds to your playing, giving an authentic feel when you dig in.
Kill Filter, another one-knob plugin, is a DJM-style resonant high-pass/low-pass filter with a kill switch.
The filter is fed into the Reyes 303 saturation model, making it an ideal and easy way to produce aggressive, textured filter sweeps.
The plugin is fully automatable and MIDI-assignable, making it a performative tool.
Both freebies are available in AU and VST3 formats for macOS and Windows.
If you enjoy Reyes 303 and want more, Triode is a full-component model of the vintage H303 amp, with an oscilloscope, spectral viewer, and impulse-response loader.
For more guitar-related content that won’t cost you a penny, check out Vales Audio’s Feedback Emulator from this year’s KVR Developer Challenge.
Download: Harmony H303 plugins (Reyes 303 & Kill Filter – FREE; Triode – $39.99)
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Last Updated on July 15, 2026 by Tomislav Zlatic.
