12AU7 (mu: 17): Released – October, 1946. See reviews

• Direct Replacement or Higher Quality
  • ECC82, ECC802, E80CC*, E82CC, E2163, B749, B329, CV491, CV4003, M8136, 5814, 5963, 6067, 6189, 6350, 6670, 6680, 7030, 7316, 7318, 7489, 7730,
• Requires Modifications
  • 12bh7*, 6fq7**, 6gu7**, 6cg7**, 6dj8**, 6AQ8**
• Variants
  • 12au7(A) – low-microphonic version

12AT7 (mu: 62): Release – May, 1947. See reviews

• Direct Replacement or Higher Quality
  • ECC81, ECC801, ECC801S, E81CC*, E180CC, A2900, B152, B309, E2157, CV455, CV4024, M8162, TS65, 5965, 6060, 6201, 6211, 6414, 6677, 6679, 6829, 7062, 7728, 12av7*
• Variants
  • 12at7(A) – low-microphinic version
  • WA, WB, WC – rugedized versions with low-microphonic and noise. WC is the final version.

12AX7 (mu: 100): Released – September, 1947. See reviews

• Direct Replacement or Higher Quality
  • ECC83, ECC803, E83CC*, E803CC, B339, B759, E2162, CV492, CV4004, CV4035, CV8156, CV8222, F6057, E2164, M8137, M8214, 6L13, 12ad7*, 12df7, 12dt7, 5721, 5751, 6057, 6681, 7025, 7058, 7494, 7729, 12BZ7*,
• Requires Modifications
  • 6n2p**, 6eu7**, 7308**
• Variants
  • 12ax7(A) – low-microphonic version
  • WA – rugedized version with low-microphonic and noise

6DJ8 (mu: 33): Released – May, 1958. See reviews

• Direct Replacement or Higher Quality
  • Cca, ECC88, E88CC, E188CC, E288CC*, ECC189, 6BQ7A, 6Н23П (6N23P), 6N11, 7DJ8/PCC88****, PCC189****, CV2492, CV2493, CV5331, CV5358, M3624, 6922, 7308
• Variants
  • There are no variants for 6DJ8 due to its later production date.

6SN7 (mu: 20): Released – March, 1941. See reviews

• Direct Replacement or Higher Quality
  • ECC32, ECC33, VT-231, CV278, CV1986, CV1988, 6H8C (6N8S), 6H8П (6N8P), 6Н8М (6N8M), 6SN7-DDR, B65, E1606, QA2408, OSW3129, 1578, 1633, 5692, 6042, 6180
• Requires Modifications
  • 6f8g***, 7n7***, CV898***, 12au7*** (family)
• Variants
  • 6sn7(GT) – early version of this tube
  • A, L – early ruggedized versions
  • W – rugged military version, glass envelope with metal band
  • WGT – the final ruggedized version with heater-cathode voltage uprated from 100v to 250v
  • GTA – improved uprated version – plate dissipation 7.5w
  • GTB – controlled warmup version of GTA

6SL7 (mu: 70): Released – June, 1941. See Reviews

• Direct Replacement or Higher Quality
  • ECC35, VT-229, CV171, CV569, CV1984, CV1985, CV3985, 33S29*, 6SC7, 6SU7, 6SL7_DDR, 6H9C (6N9S), 6H9П (6N9P), 6Н9М (6N9M), 1655, 5691*, 6113, 6188
• Variants
  • Same as 6SN7 above

12BH7 (mu: 16.5): Released – May, 1950. See Reviews

• Direct Replacement or Higher Quality
  • ECC99, CV5042, E80CC, 6CG7/6FQ7***, 6sn7***
• Variants
  • 12bh7(A) – low-microphonic version

7199 (triode mu: 17): Released – October, 1958 See Reviews

• Requires Modifications
  • 6BL8***, 6U8(A)***, ECF80***, ECF82***, 6C16***, CV5065***, CV5215***

If you see anything missing from the list, please add to the comments.

Legend:
* Higher heater current
** Requires circuit modification
*** Requires adapter
**** Higher voltage variant (usually works fine)

Related Post: Soviet/Russian Tubes Equivalents