6J5

The 6J5 is a single-triode octal tube that is essentially one half of a 6SN7, with a mu of ~20 and plate resistance of ~7.7k ohms. Using two separate 6J5s instead of one 6SN7 eliminates crosstalk between sections and allows independent tube selection for each channel, which purists argue yields a blacker background and better channel separation. The tube was ubiquitous in 1940s radio and early television and is readily available as NOS in large quantities at modest cost. Its single-triode construction makes it a natural choice for minimalist preamp designs where each gain stage gets its own dedicated tube.