StringsTheory Design

Circuit analysis for
tube amp builders

Five precision tools in one app — tonestack calculator, PSU simulator, load line plotter, tube database, and build planner. Native on Mac and iPad.

macOS 15.7+ · iPadOS 18.0+ · One-time purchase Free · No accountmiddot; No account required · Works offline

Five tabs. Everything you need.

Each tool is purpose-built for tube amplifier design and analysis.

See the tone before you build

Real-time Bode magnitude and phase plots for 53 guitar amp tone circuits across 9 categories. Adjust virtual potentiometers with realistic taper curves and see the frequency response update instantly.

✓ 53 tone circuit models: Fender (12), Marshall, Vox, Dumble, Baxandall, James, Big Muff, Boss, SWTC, and basic RC filters
✓ Real-time Bode magnitude and phase plots (10 Hz to 100 kHz)
✓ Adjustable pot tapers: Linear, Log A, Log B, Log C
✓ Compare multiple tonestacks with color-coded overlaid curves
✓ Edit component values with E24 series stepping
✓ Square wave oscilloscope via state-space simulation
✓ Save and load configurations as JSON

Simulate your power supply

Time-domain simulation using Euler integration with Newton-Raphson convergence. Design filter chains, compare rectifier topologies, and see voltage ripple and current waveforms in real time.

✓ 4 rectifier topologies: full-wave CT, bridge, voltage doubler, half-wave
✓ 173 rectifier tube models with manufacturer I-V curves
✓ Configurable C, RC, and LC filter stages with ESR
✓ Newton-Raphson convergence for nonlinear tube/diode behavior
✓ Voltage and current trace visualization with zoom and pan
✓ Mains frequency selection (50/60 Hz)
✓ Load and save in PSUD2-compatible .psu format

Find the operating point

Plot plate characteristic curves for EL34, 6L6GC, 6V6GT, 300B, and dozens more. Overlay DC and AC load lines, drag the Q-point, and see power dissipation update live.

✓ ~50 tube parameter sets: 12AX7, 6L6GC, EL34, EL84, 6V6GT, 300B, 2A3, KT88, and more
✓ Koren triode, pentode, and unified tube models
✓ Single-ended and push-pull topologies
✓ Pentode, ultralinear, and triode operating modes
✓ Draggable Q-point for interactive exploration
✓ Power dissipation curve overlay (max plate watts)
✓ Output power, headroom, and effective mu calculations

3,727 tubes at your fingertips

Search by designator, category, or base type. Every entry includes heater specs, maximum ratings, operating conditions, and pinout diagrams. Rectifier tubes include verified max input filter cap ratings.

✓ 3,727 tube entries across 11 categories
✓ Visual pinout diagrams: Octal, Noval, Compactron, Rimlock, Loctal, Magnoval, UX-4, B7G
✓ Heater voltage/current, max plate voltage, max plate dissipation, screen voltage
✓ Operating conditions: plate current, Gm, rp, mu
✓ Max input filter capacitor ratings for 90 rectifier tubes — individually verified from original manufacturer PDFs
✓ Substitute recommendations and datasheet links

On rectifier cap values: Every max filter capacitor value was individually verified by reading the actual manufacturer PDF datasheet. We caught and corrected errors in commonly cited values for the 5Y3GT (20 uF, not 40), WE274B (4 uF, not 40), 5V4GA (10 uF, not 40), and GZ37 (not specified, not 60).

Plan the build, match the transformer

Load a Fender Deluxe Reverb, Marshall JCM800, or any of 479 amp presets. The calculator shows heater rail currents, B+ requirements, and recommended mains fuse, then matches against transformer catalogs.

✓ 479 amplifier references across 30 manufacturers
✓ Verified mains fuse data for 346 models
✓ Transformer matching — Hammond, Edcor, Mercury Magnetics, Pacific
✓ Fixed bias, cathode bias, and relay power configurations
✓ Automatic heater rail grouping and secondary synthesis

67 articles. Searchable. Context-sensitive.

Built-in help system with step-by-step guides, worked examples, safety warnings, and a 30-term glossary. Opens to the relevant section for whatever tool you're using.

✓ 67 help articles across 5 tool sections
✓ Context-sensitive — opens to current tab
✓ Searchable across titles, summaries, and keywords
✓ Numbered step-by-step guides for every tool
✓ Worked examples with real component values
✓ Safety warnings for high voltage and capacitor limits
✓ 30-term glossary (Bode plot, Koren model, load line, and more)
✓ Localization framework for 6 languages

Common questions

Does the app require an internet connection?

No. All features work fully offline. The app optionally checks for announcements but never requires internet access.

Is the tube data accurate?

Sourced from manufacturer datasheets (RCA, Mullard, Philips, GE, Tung-Sol). Rectifier max filter capacitor values individually verified from original PDFs.

What file formats does it support?

JSON for tonestack configurations. PSUD2-compatible .psu format for power supply designs.

Is there a Windows version?

No. StringsTheory Design is built with native SwiftUI for Mac and iPad only.

Is there a subscription?

No. One-time purchase — no subscriptions, no in-app purchases, no ads, no data collection.

How do I report a bug?

Email info@stringstheoryinv.com

Tonestack Models	53 across 9 categories
Rectifier Models	173 with manufacturer I-V curves
Tube Database	3,727 entries with pinouts and ratings
Rectifier Cap Data	90 tubes with datasheet-verified max C1 values
Tube Parameter Sets	~50 for load line plotting
Amplifier References	479 across 30 manufacturers
Verified Fuse Data	346 amplifier models
Help Articles	67 with search, glossary, and worked examples
Transformer Catalog	Hammond, Edcor, Mercury Magnetics, Pacific
File Formats	JSON (tonestacks), .psu (PSUD2 compatible)
Platforms	macOS 15.7+, iPadOS 18.0+
Price	One-time purchase
Internet Required	No — fully offline
Languages	Terms in 6 languages; help in English (more coming)
Privacy	Zero data collection, no tracking, no analytics

Circuit analysis fortube amp builders