OhmNote: Electronics Tube Amp

Sang Truong

In-app purchases

About this app

OhmNote is the electronics calculator that finally takes vacuum tubes seriously.

Whether you're designing a valve amplifier, winding a transformer, restoring vintage gear, or just learning Ohm's law, OhmNote puts many precise, beautifully crafted tools in your pocket - and it all works completely offline, with no ads and no account.

From a quick resistor color-code lookup to plotting a load line and winding your own output transformer, it's the rare toolkit that covers everyday electronics AND the deep tube-amp math most apps ignore.

⚡ BUILT FOR VACUUM-TUBE ENTHUSIASTS

Tube Analyzer - plot the load line, set the Q-point, and read gain, set bias, estimate distortion and more in real time
Tube database - specs, operating points and applications for hundreds of tubes
Tube pinouts - clear base diagrams at a glance for thousands of tubes
Tube substitution - find compatible replacements and equivalents
Tester settings - ready-to-use setups for popular tube testers

🧲 TRANSFORMERS & MAGNETICS

Output transformer (OPT) designer - turns ratio, primary inductance, air gap and saturation check
Power transformer designer - VA, turns-per-volt, every winding and its wire gauge
Gapped-core choke designer for power-supply filtering
Air-core inductor (Wheeler) - turns ↔ inductance, both directions
Transformer ratio & impedance, plus wire gauge (AWG ↔ SWG ↔ mm)
Inductive Reactance of coil or transformer - inductance ↔ impedance ↔ frequency

🔧 EVERYDAY ELECTRONICS

Ohm's law & power - solve for any value
Resistor color code (4/5/6-band + SMD) - read or generate
Capacitor code decoder, LED resistor, voltage divider
Series/parallel resistors, capacitors and inductors
Reactance, RC/RL time constants, resonant frequency
dB converter, frequency ↔ period

🔌 POWER & SIGNAL

Adjustable regulator (LM317 family) with heat & heatsink check
Zener regulator designer
Stepped attenuator (log volume control) designer
RC/RL passive filters with drawn schematics
Resistor & capacitor combination finder
Connector pinouts - USB, HDMI, VGA, RS-232 and more

✨ WHY YOU'LL LOVE IT

We meticulously perfected every feature; experience the difference for yourself.
Solve forward OR reverse - enter what you know, get what you need
Smart SI-unit input - just type 4.7k, 100n, 1M…
Instant results as you type
Fully offline - no internet required
No account, no ads, privacy-first
Gorgeous light & dark themes
Keep adding and enhancing features time to time
Available in English, Vietnamese, Spanish, French and German

OhmNote is made for guitar and hi-fi amp builders, audiophiles, ham radio operators, repair techs, students and working engineers - anyone who wants fast, trustworthy answers without the clutter.

Download OhmNote and build with confidence.

What’s new

• Tube analyzer now opens at each tube's datasheet operating point.
• Load impedance range now comes from the tube instead of a fixed limit.
• Fix Tube Database feature for showing pinout and tube subtitution.
• Russian designations (6Л6, 6Н3П…) now find the right tube.
• New tube: 26 (UX-226).