There are a specific Military Grade Chinese 12AX7 tube that Mesa used back in the late 80's through the 90's. Often referred to as the Beijing Square Foil Getter tube. Their part number was 6N4-J. Ruby has sold them as there is still a supply of them. They were not made by Shuguang but they did start producing similar looking tubes. Different construction and had a round halo getter. Usually sold by Ruby or Penta Labs, I only had three of them as part of a retube set, they were super microphonic I could not use them. There are other Chinese tubes offered by Ruby which is more of a 7025 variant. Not a bad tube. I much prefer the Beijing Square Foil Getter tube, 6N4-J or Chinese Military grade Beijing tube. They look like this:
The one's with the halo getter are also referenced as Silver Specials. They are not the same tube. The first picture has the Mesa tubes on the left and the Ruby on the right. Best set of tubes I ever used in the Roadster, tightened up the low end and I can actually use a 7-string without all the mud. It actually sounds really sic for that sinister character of the low B. I much favor the STR440 tubes, usually in the yellow bias color or red bias color (these actually sounded really good). The next best option would be the STR445, I would not go higher than yellow bias color as that resulted in a distorted clean channel. Red or yellow for the Mesa STR445.
As for the EHX tubes, they are Russian tubes. It is just a trade name owned by New Sensor that manufactures their tubes at the Saratov factory, called Reflektor. I think the factory name changed a while back. Tubes made in St. Petersburg were made by SED aka Svetlana Electron Devices, however back in the 90's New Sensor bought the Svetlana trade name so those tubes are made by Reflektor and not Svetlana in St. Petersburg. If you ever see SED =C=, those tubes were made in St. Petersburg. They stopped production of consumer products sometime around 2012-2013. In my opinion the SED =C= EL34 and the 6L6GC were some of the best sounding power tubes next to the Sylvania STR415 or RCA black plate tubes. They did manufacture 12AX7 tubes but were not known for having a good preamp tube.
New Sensor tubes out of NY, broker tubes made by Reflektor in Saratov Russia: Mullard, EHx, Tung Sol, Gold Lion, Svetlana, Sovtec, and Reflektor brands. I am probably missing something in the list. Most are good tubes but not always compatible with the tone stack driver (DC coupled cathode follower) usually in the V3 position and the FX tube typically found in V4 or V5 depending if the amp has a tube driven reverb circuit like the Roadster.
V3 is the DC coupled cathode follower tone stack driver. V4 is for the FX loop, one triode is a cathode follower. V4B. This amp is different than the Roadster, V5A is the driver tube for the reverb tank but V1B is the recovery stage. V6 is the phase inverter.
What can add noise to the sound: any of the preamp tubes. I found that many of the Russian tubes tend to generate a low frequency hum (EH, Tung Sol, Mullards) this usually occurs after a few months of use. They usually do not age in silence. Not always true, depends on the heater source.
The Rectifier tubes are also contributors. Even when using Diode tracking, the 5U4GB tubes are still in the power circuit and will provide rectified current as they will be operating in parallel. As they age, they will create noise.
The other Chinese tubes if I can recall come from Ruby or Preferred series, generally classified as 7025 tubes but are the same thing as a 12AX7 or ECC83.
The last source of noise will be the Power tubes.
Sounds like you may need some preamp tubes to start with Don't forget the 5U4GB rectifiers either. If you can find the Beijing Military Grade Square Foil getter tubes, great, may be harder to find than it seems. Note that some people have been selling them but I can tell they were near end of life, there are two mica spacers just above the plates, if that area is black or silver and not clear, they are well used tubes. That area becomes discolored over time.
Another difficult tube to get are the Mesa (JJ ECC83s) tubes. They sell out quickly when the inventory comes into the market. I waited almost 6 months to get the STR445 tubes and 4 months to get the Mesa 12AX7. The lead time for the STR445 tubes is long, Sweetwater no longer has them listed as items to purchase. AMS had them listed as active, but the lead time was longer than expected.
Places that sell Mesa gear should have the tubes as well. The STR448 may not be to your liking, I tried them in my MWDR and Roadster and did not care for the character.
