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 can be 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