The tubes are listed as 5881 5881 7025 7025 12AX7 12AX7 7025 7025 in a little chart inside the cabinet.


This is an explanation from a guy that helped me understand what was going on.

Back in ye olden days, 7025 was the designation for a low-noise, low-hum 12AX7 for hi-fi purposes. This only applies to NOS tubes, modern tube makers mix and match all the old tube designations the same way they use old company names...it's just whatever the marketing department decide to call the tube.

In the Concert, the two 12AX7 are 3/5 of the tremolo circuit, they don't see the guitar signal and their fidelity doesn't matter, so Leo could use whatever 12AX7 he wanted there. Counting from the input side of the amp...
V1 - First two stages of Normal channel
V2 - First two stages of the Vibrato channel
V3 - Drives the LFO for the harmonic tremolo circuit
V4 - (only 1/2 the tube used) - LFO inverter for the harmonic tremolo circuit
V5 - Low- and high-pass amplification stage for the harmonic tremolo circuit
V6 - Long tail phase inverter
If you want modern tubes, the popular modern choices are the Tung Sol and Mullard 12AX7, both made in Russia at the same factory. You can buy them just about anywhere, find a dealer who has reputation for good customer service.

NOS? These are getting even more expensive and less trust worthy as stocks thin down (more and more I run into have some sort of hiss or static). But KCA NOS Tubes, Tube World, and Brent Jessee Recording or probably the best resources.

So yeah, will replace the tubes in v1 and v2 with the NOS I am getting, then move one of those GE made 7025 tubes into V3 where the microphonic old Tung-sol 12AX7 was and keep one 7025 in reserve.

Will also start looking for some NOS 5881's or 6L6WGB's (same thing, but toughened up for military use) to hold in reserve should the ones I have go out.