StringsTheory Design

Circuit analysis for
tube amp builders

Eight precision tools in one app — tonestack, PSU designer, load lines, bias, tube data, semiconductors, circuit calcs, and build planner. Native on Mac and iPad.

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

Eight 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 52 guitar amp tone circuits across 9 categories. Adjust virtual potentiometers with realistic taper curves and see the frequency response update instantly.

✓ 52 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.

✓ 109 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
✓ Distortion analyzer — harmonic estimate via RDH4 ordinate methods

Bias it right, three ways

Three bias methods with a live plate-dissipation gauge and a power-tube quick-select. Handles fixed and cathode bias.

✓ Target-dissipation method — pick a percentage of max plate watts, get the target current
✓ Cathode-resistor method — bias from a voltage reading across the cathode resistor
✓ Direct current measurement — enter measured plate current straight from the meter
✓ Live plate-dissipation gauge — green / amber / red against the tube’s maximum
✓ Power-tube quick-select for common output tubes
✓ Fixed bias and cathode bias supported

Bias calculator on iPad — three bias methods with plate-dissipation gauge

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 88 rectifier tubes — individually verified from original manufacturer PDFs
✓ Substitution checker — a 5-criteria engine rates each swap (identical / works with a different result / rebias required / not recommended) and explains why
✓ Datasheet links for every entry

~9,000 solid-state parts, not just tubes

A searchable database of roughly 9,020 transistors, diodes, and ICs with package pinouts, ratings, and substitution suggestions — for the solid-state stages, rectifiers, and effects that live alongside the tubes.

✓ ~9,020 transistors, diodes, and ICs
✓ Package pinout diagrams
✓ Ratings at a glance — voltage, current, dissipation
✓ Substitution suggestions

Semiconductors database on iPad — 2N3392 entry with specifications and TO-92 pinout

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 31 manufacturers
✓ Verified mains fuse data
✓ Transformer matching against 90 catalog models — Hammond, Edcor, ClassicTone, Mercury Magnetics, Heyboer
✓ Fixed bias, cathode bias, and relay power configurations
✓ Automatic heater rail grouping and secondary synthesis

17 bench calculators for every stage of design

Seventeen stage, component, and reference calculators covering the rest of the signal path — math verified against Valve Wizard, RDH4, and Aiken references.

✓ Stages: Cathode Bypass, Gain Stage, Cathode Follower, Phase Inverter
✓ Loop & response: Feedback / Presence, RC Filter, Miller Capacitance, Clipping
✓ Output: OT Matcher, Speaker Impedance, Cab Wiring, L-Pad
✓ Modulation & utility: Tremolo Oscillator, Ohm’s Law, Voltage Divider, LED Dropper
✓ Standard Values (E-series) rounds any result to real parts
✓ Math verified against Valve Wizard / RDH4 / Aiken

Circuit Calcs on iPad — Cathode Bypass calculator with live results

61 articles. Searchable. Fully localized.

Built-in help system with step-by-step guides, worked examples, safety warnings, and a 44-term glossary. Opens to the relevant section for whatever tool you're using.

✓ 61 help articles across every tool
✓ 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
✓ 44-term glossary (Bode plot, Koren model, load line, and more)
✓ Fully localized — the entire app UI and all 61 help articles in English, Spanish, French, German, Japanese, and Italian

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	52 across 9 categories
Rectifier Models	173 with manufacturer I-V curves
Tube Database	3,727 entries with pinouts and ratings
Rectifier Cap Data	88 tubes with datasheet-verified max C1 values
Tube Parameter Sets	109 for load line plotting
Semiconductor Library	~9,020 transistors, diodes, and ICs with pinouts
Circuit Calculators	17 — verified against Valve Wizard / RDH4 / Aiken
Amplifier References	479 across 31 manufacturers
Verified Fuse Data	Included — verified from manufacturer data
Help Articles	61 help articles + 44-term glossary, with search and worked examples
Transformer Catalog	90 models — Hammond (43), Edcor (30), ClassicTone (9), Mercury Magnetics (7), Heyboer (1)
File Formats	JSON (tonestacks), .psu (PSUD2 compatible)
Platforms	macOS 15.7+, iPadOS 18.0+
Price	One-time purchase
Internet Required	No — fully offline
Languages	Full app UI and all help articles in 6 languages — English, Spanish, French, German, Japanese, Italian
Privacy	Zero data collection, no tracking, no analytics

Circuit analysis fortube amp builders