It probably would not surprise anyone to learn that while there are thousands of different tube numbers, many of these are just the same electronic type with a different envelope or different basing. The list below gives 4, 5, 6, and 7 pin types and their octal equivalents. In some cases, the loktal and miniature equivalents are given also. The types given are electronically identical, except for some small interelectrode capacitance differences due to differences in construction, and, given the appropriate adaptor or socket change, will, in most cases, work as direct substitutes. These vary from the well known (a 5Y3 is the octal equivalent of the 80) to the obscure (a 6Y7G is the octal equivalent of the type 79). Hopefully you will find the following table useful as some of these tubes become scarce.
| 4,5,6,7 Pin | OCTAL | LOKTAL | Miniature |
| 1A4 | 1D5G | ||
| 1A6 | 1D7G | ||
| 1B4 | 1E5G | ||
| 1B5 | 1H6G | ||
| 1C6 | 1C7G | ||
| 1F4 | 1F5G | ||
| 1F6 | 1F7G | ||
| 5Z3 | 5U4G, 5X4G | ||
| 6A3 | 6B4G | ||
| 6A6 | 6N7G | ||
| 6A7 | 6A8G | 7B8 | |
| 6B5 | 6N6G | ||
| 6B7 | 6B8G | ||
| 6D6 | 6U7G | ||
| 6F7 | 6P7G | ||
| 25Z5 | 25Z6G | ||
| 30 | 1H4G | ||
| 41 | 6K6G | 7B5 | 6AR5 |
| 42 | 6F6G | ||
| 43 | 25A6G | ||
| 75 | 6B6G | 7B6 | |
| 76 | 6P5G | ||
| 77 | 6J7G | ||
| 78 | 6K7G | ||
| 79 | 6Y7G | ||
| 80 | 5Y3G, 5Y4G | ||
| 83V | 5V4G | ||
| 84/6Z4 | 6X5 | 7Y4 | 6X4 |
| 85 | 6V7G | ||
| 950 | 1J5G | ||
| 951 | 1E5G | ||
| 1A5GT | 1LA4 | ||
| 1E4G | 1LE3, 1LF3 | ||
| 1H5GT | 1LH4 | ||
| 6G6G | 6AK6 | ||
| 6J5GT | 7A4 | ||
| 6R7GT | 7E6 | ||
| 6SF5 | 7B4 | ||
| 6SK7 | 7A7 | ||
| 6SL7GT | 7F7 | ||
| 6SN7GT | 7N7 | 6CG7 | |
| 6V6GT | 7C5 | 6CM6 | |
| 12A8GT | 14B8 | ||
| 12SN7GT | 14N7 | ||
| 35Z4GT | 35Z3 | ||
| 35Z5GT | 35Y4 | 35W4 | |
| 117Z4GT | 117Z3 | ||
| 2050 | 2D21 |