| U.S.Amps | Car Tube Amplifiers |
| Uda directory 2000-01-13 | Japanese DIY Tube Amplifier |
| Udo s oldradio | Vintage Radio Collector |
| Uesugi by Teac | Tube Amplifiers |
| UHF Magazine | Magazine |
| uk.rec.audio | Newsgroup |
| UL Sound | Tube Amplifiers |
| Ulrich Haumann's Vintage HiFi Pages | DIY Vintage Hifi |
| Ultimate Audio | Audio Magazine |
| Ultra Fi | Ultrafi webring |
| Ultraaudio | Information about Tube Audio - Articles |
| UltrAnalaog | DIY Tube Amplifier |
| Ultrasound | Tube Amplifiers |
| Ultratone Amplifier & Supply Company | Tube Guitar Amplifiers, Tube Guitar Amplifier Kits |
| Uncle Spot webpage | Tube Guitar Amplifier Restoration, Tubes |
| Uncommon Audio | Speakers |
| Unison Research | Tube Amplifiers, Tube CD Player |
| United Home Products | Retailer, Pics |
| Universal Audio | Tube Electronics for Professionals |
| Universal Radio | Ham Radio |
| Universal Vacuum Tube Amplifier Fugaku and his Fellows | Japanese modular Tube Amplifier |
| Univox | Tube Guitar Amplifiers, Museum |
| Unofficial Dynaco Home Page | Museum, Schematics |
| Uptown Audio | Retailer |
| Used Vintage Salvage | Vintage Tube Audio Equipment |
| Usher Audio Technology | Speakers |