Here is small list of octal tubes that i could recommend to use with little dot.
6SL7GT = VT-229 Classic type
6SL7WGT Rugged version with smaller parts
6SL7WA Military version
6SL7GTB Lower base
6SU7GTY Better quality and balance? Tung-Sol
6SU7WGT = 6188 Ruggedized and bantam construction
ECC35 European version with 0.4A heater
6N9S (6H9C) Russian
6N9M (6H9M) Russian mini version
1579 Russian, better quality?
6N9P-T Chinese, better quality?
6113 Low microphonic?
5691 Better quality? 0.6A heater
6SN7GT = VT-231 Classic
6SN7GTA More power?
6SN7GTB Like -A but with faster heating
6SN7GTY = CV1988 Better quality?
6SN7WGTA Ruggedized and bantam construction
5692 Better quality?
6N8S (6H8C) Russian
1578 Russian, better quality?
6N8P-T Chinese, better quality?