| K & K International | Test Equipment |
| K & M Analog Designs Two-Rock.Com | Tube Guitar Amplifiers |
| K9GD Home Page - Streamwood, Illinois | Amateur Radio Station |
| Kalamazoo Guitar Amps | Museums, Tube Guitar Amplifiers |
| Kaluga | Tubes |
| Kamakura | DIY Tube Amplifiers |
| Kame | DIY Tube Amplifiers, Tubes |
| Kankyu Amplifier | Tube Amplifiers |
| Kanno Music System Co. Ltd. | Tube Amplifiers |
| Kasman Audio | Vintage Amplifier Restorations, Sale |
| Katelelo Audio | DIY Tube Amplifiers |
| Katoh K | DIY Tube Amplifiers |
| Katsu-san- | DIY Tube Amplifiers |
| KAVD | Tube Hybrid Amplifiers |
| Kaz Kobayashi's Home Page | DIY Tube Amplifiers |
| Kazuhiro Katoh | DIY Tube Amplifiers |
| Kazuhiro Sunamura | Radio Amateur |
| KBápps.com | RCA Receiving Tube Manual |
| Kbrooksaudio | Speakers |
| KCA NOS Tubes | Tubes, Information about Tube Audio - Articles |
| Kelind | Tube Amplifiers |
| Ken Gilbert | DIY Tube Amplifiers |
| Kendrick Amplifiers, Guitars & Necessities | Tube Amplifier Services |
| Ken's Electronics | Tubes, Parts |
| Kepco Inc. | Power Supplies |
| Keystone Electronics Corp. | Standoffs, Fuse Holders |
| Kikuchi | DIY Tube Amplifiers |
| Kilokat's Antique Light Bulb Collector's Site | Collection |
| Kim | DIY Tube Amplifiers |
| Kimber Cable | Cables, Capacitors |
| Kimura Tetsu | DIY Tube Amplifiers |
| Kingsley Amplifiers | Tube Guitar Amplifiers |
| Kishi's Audio Room | DIY Tube Amplifiers, Forum |
| Klangfilm Home! | Speakers |
| Klare | Tube Amplifiers, Transformers, Tubes |
| Klaus Schiffer audio | DIY Tube Amplifiers, Information |
| KlausMobile English Index Page | DIY Tube Audio, Information |
| Klimo | Tube Amplifiers, Speakers |
| Klipsch | Speakers |
| Klubben.net | Retailer |
| Knight-Kit | Ham Radio |
| Koch Opening | Tube Guitar Amplifiers |
| Kombi | Tubes |
| Komet Amplification | Tube Guitar Amplifiers |
| Kondo | Retailer of KONDO |
| Kondo - Audio Note | Tube Amplifiers, DAC's, Speakers |
| Kora | Tube Amplifiers, DAC's |
| Korato | Tube Amplifiers, Tubes |
| Kosuge Sinkuu | DIY Tube Amplifiers |
| Kozakai Denshi | Tubes, Parts, Radios |
| KR Audio | Tube Amplifiers, Tubes |
| kr Audio Products | Retailer |
| Krank Electronics & Speaker | Tube Guitar Amplifiers |
| Krypton | Retailer, Tube Amplifier Kits |
| Krystal Clear Audio - Video | Retailer |
| KT88_ValveAmp | DIY Tube Amplifiers |
| K-tronics, Inc. | Resistors |
| Kudelski Group | Tube Amplifiers |
| Kunio | DIY Tube Amplifiers |
| Kurt Strain's Tube Odd-e-o-file Page | Tube Circuits, speaker projects and more |
| Kustom Amplifiers | Tube Guitar Amplifiers |
| Kusunoki | DIY Tube Audio Site |
| Kutloch | Information |
| KW Tubes | Tubes |
| Kwang Woo Electronics Co., Ltd. | Tube Amplifiers |