| I. G. Electronics | Professional Audio Equipment |
| IAG | Tube Amplifier, Tube Amplifier Kits |
| ICL's Audio Products Information and Control Laboratory | Tube Amplifiers |
| ICO Rally | Braids, Tubings & Heat Shrinks |
| Icon Audio | Tube Amplifiers |
| Iconic Speaker Manufacturing | Speakers |
| ICW | Capacitors |
| Ideal Innovations | Tube Amplifiers |
| IFI | RF Tube Amplifiers |
| IGA Valves Bilbao | Tube Seller |
| Ikarus Audio | Tube Amplifier, Tube Amplifier Kits |
| Il sito web Musictubes | DIY Tube Amplifiers |
| image hifi | German Audio Magazine |
| Imaico | Japanese Audio Distributor, Dealer |
| Inca Rock | Tube Amplifiers |
| Infinitude | DIY Tube Amplifiers |
| Infotronix | Manuals, Schematics |
| Inner Ear Report | Audio Magazine |
| INnovative Audio | Tube Amplifiers, Tubes, Speakers |
| insidehi-fi | British Audio Trade Journal |
| Interconnect2000 | Braids, Tubings & Heat Shrinks |
| International Rectifier | Resistors |
| Internet Audio Fans Club | Links |
| InterStudio | Tubes |
| Intertechnik | Speakers and Components |
| Intertrafo | Transformers |
| Island Audio | Retailer, Books & Software |
| Isym | Information about Tube Audio - Articles |
| Izzy Wizzy | DIY Tube Audio Site |