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I have a Little Bear T11 vacuum tube phonograph pre-amp. It has three
Shuguang 6N2-J "Military Grade" vacuum tubes which I want to upgrade. The pre-amp also has a Chinese made 6z4-J Rectifier. The amp also has a switch by each of the three 6n2-J tubes marked 6n2/12ax7 so either can be used.

My questions:

  1. What tubes are the equivalent for Chinese 6n2-J tubes?
  2. If I go with 12ax7 tubes, which are way more easy to find, do I need to change the 6z4 rectifier because of the voltage difference or is it good to go?? On the unit there is no switch for the rectifier like the other tubes do and is just labled 6z4.
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    \$\begingroup\$ Do you have any schematics at all? \$\endgroup\$ – Hearth Jan 21 at 0:48
  • \$\begingroup\$ If the two valves are equivalent, why would the power supply valve need to be changed? \$\endgroup\$ – Chu Jan 21 at 1:00
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The 12AX7 contains 2 filaments which can be connected in series (for 12 volt operation) or in parallel (for 6 volt operation). The 6N2J is similar to the 12AX7 except that the filaments are permanently wired in parallel so only 6 volt operation is possible. I assume that the switch next to each 6N2J tube in your pre-amp is arranged to connect the 12AX7 filaments in parallel so that it will operate properly with a 6 volt supply. There is no need for such a switch for the rectifier tube since it is not intended to replace it with a 12 volt substitute.

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