TUBE CROSS REFERENCE BASICS
There have been a myriad of tubes types and styles made over the years for industrial, military and commercial use. Many of these use European nomenclature. A cross reference is included here:
| Groove Tubes | Industrial | European |
| GT-12AT7 | 6679 | ECC81 |
| GT-12AU7 | 6189 | ECC82 |
| GT-12AX7 | 7025 | ECC83 |
| GT-5AR4 | - | GZ34 / GZ37 / U54 / U77 |
| GT-5U4 | - | GZ32 / GZ31 / U51 / U52 |
| GT-5Y3 | 6853 | GZ30/U50 |
| GT-7025 | 7025 | ECC83 |
| GT-6CA4 | - | EZ81 |
| GT-ECC83 | 7025 | ECC83 |
| GT-6L6 | 5881 | KT66 |
| GT-6V6 | 7048 / 5871 | - |
| GT-6550 | 6550 | KT88 |
| GT-EL34 | - | 6CA7/KT77 |
| GT-EL84 | - | 6BQ5 |