Power tube fried... Replace 2 or 4?

[groovebelly]

6L6 next to 5UGB lit up like my Christmas tree and then the
fuse blew ...

Should I replace 2 or 4 tubes?

 

[espboogie123]

Theoretically you can replace that one tube with same brand if tube is in same bias range. Most tube vendors sell in match pairs. I think dougs tubes sells singles. If it were me, I would just replace all four tubes for peace of mind and future reliability.