It can be hit or miss when it comes to NOS as they are not tubes you find at every resource like you would get with current production. The added cost due to limited resources, is it worth the risk?
I had bought a few (NOS): RFT12AX7 and some EiCV492 (these were commonly used as Mullard counterfeit tubes, they are good tubes though). Neither of these ever made its way into any of the Dual Rectifiers I have. They found their home in two amps, Royal Atlantic RA100 Head and Combo. RFT in V1 and Ei in V2 and Ei in the phase inverter. Rest remained the same stock tubes. I will say the Hi gain and lo gain never sounded better. Both amps completed with NOS Mesa STR442 SED =C= EL34. I bought a few sets of those, also had some I bought from the Tube store just when Svetlana Electron Devices stopped making the 6L6 and EL34 tubs. Not the same tube as the new production Svetlana as they are made by Reflektor (New Sensor that makes the TungSol EH, and so on).
Never thought about using the RFT in the Roadster, if I did and may have done so, it may not have been that rewarding or ended up with too much low end. The RFT has an interesting characteristic, when used in a typical triode circuit with 100K plate resistor, it will sound very similar to the Mesa 12AX7 (JJ ECC83s). However, when it gets driven into hard clipping it takes on a new characteristic with an aggressive tone that is not the same as the JJ ECC83s. Sub-harmonic content is evident. It emulates the cold clipper circuit used in the Dual Rectifier usually in the V2 position. Enough said. Different amp.
I had in my possession 10 of the Mesa 12AX7 tubes from 1990. Tube removals from the Mark III I held onto when I was changing all tubes every 8 months. The preamp tubes were all in good shape, some with less than 3 months and some with a bit more. Every single one of them tested really good. Where to use them? A few years back, Doug's tubes and some inventory of the Ruby Square Foil getter tubes of that era, claimed not to be used in the V1 position but will work everywhere else. Bought 10 of those. Tried them mostly in the Mark V90 as I was struggling to get to bond with that amp. I gave up and installed all original Mesa (JJ ECC83s) tubes in the amp as I was considering selling it. Tubes on the left are the Mesa branded 6N4-J Military grade Chinese Beijing tubes. Tubes on the right are the one's brokered through Ruby Tubes (trade name used to sell the goods, not the manufacturer)
I recently cleaned up the Roadster, chassis removal, inspected around each preamp tube socket for aluminum dust caused by the rotation of the tube shields. That usually happens when installing the shields while the chassis is in the head shell. If I pull the chassis out, and change tubes then, no dust.
V1 = Mesa branded 6N4-J Beijing tube, the phase inverter has a Mullard reissue 12AX7 long plate and the rest of the tubes except for the reverb (stock mesa tube) are the Ruby Beijing tubes.
That worked out really well. Still running with the STR440 tubes. Roadster is much tighter in tone, CH3 is closer to the MWDR character, and for the first time I was able to run a 7-string guitar without any drone or mud. That was epic.
I have tried the Chines 7025, not sure what factory makes them, brokered through Ruby tubes. They would be equivalent to Groove Tubes. Not a tube manufacturer, more of a broker/distributor just like Mesa branded tubes are not manufactured by Mesa, they are certified and tested/ approved by Mesa. The Sino 7025, or in western culture, the Chinses 7025 could be made by Psvane, Shuguang, Linlai, or Guiguang (now owned by Psvane). The word Sino is not a company name, it is a reference. Sino means Chinese.
I think I experimented with them a couple of years ago. However only with V3 and V5 in the Roadster.