About the Power Supply Tubes for the WV Preamps.
The WV's tube-based power supply sounds lovely for the same reason that a tube-based audio circuit sounds lovely. And just as the tubes in the signal part affect the sound, and just as the quality of the Mains cord affects the sound, every one of these tubes affects the sound of the preamp. WVs will ship with the "house wine" grade tubes, you are encouraged to sample other types to tune the sound to your liking, and enhance your listening experience.
All of the tube types used in the power supply were made by different manufacturers and unlike such extremely-popular audio signal tubes like the 6DJ8, no one has evaluated these tubes in terms of sound quality. In addition, they were sold as "commodity" tubes, and routinely rebranded so there is little hope of tracing them back to their original manufacturer. These tube types are inexpensive and plentiful and it's fun to listen to how they change the sound. I recommend that you try any and all that you can get your hands on -- this is an ideal opportunity to tune the sound of the WV to your personal liking.
Here is the tube breakdown, and alternates:
The Rectifier Tube (V5) takes the high voltage AC output of the power transformer and turns it into unregulated DC. WVs can use 9M-based tubes like the 6CA4/EZ81, 6V4/EZ80, CV3996, CV5072, or the U709, and it can also use 6DJ-based tubes like the 6BW4. The sound of the rectifier tube has a dramatic impact on the sonics of the preamp. I have sorted through dozens of variants -- see this information. WV Standards will receive at least an AAA grade, WV XL's will receive AAAAA grade tubes.
The Pass Tube (V6) takes the unregulated DC and regulates it to a steady 250 volts DC for use by the audio circuitry. The WV can use several different pentode and tetrode tube types in this location as long as they are 9EU or 9CK-based (see bottom of page). They are connected as power triodes. 6CM6, 6DW5, 6GC5, 6973 can all be used here.
The 6CM6 (RCA) produces a warm, very present sound with great depth and width. This tube comes in two bottle heights, both labeled "RCA," and the insides look indentical. A third type of RCA-labeled 6CM6 has been identified, this with ribbed plates. This latter has a slightly leaner sound than the former two.
The Electro-Harmonix-branded 6973 has more detail than the 6CM6 and every bit as much depth, with a somewhat narrower stage. The 6DW5 (RCA) is more up-front and airier-sounding, with less depth. 6GC5s produce a detailed and transparent but relaxed sound, with good depth and width, with the the RCA-branded version standing out as possessing excellent layering and imaging.
This tube gets quite hot. In the WV it is required to dissipate 7 watts, which is well under the manufacturer rating of 10 to 12 watts. The 6GC5 has a much larger glass envelope than the other tubes and as a result runs somewhat cooler due to its larger surface area, but they should all last for many, many years.
The Error Amplifier Tube (V7) is the regulator's error amplifier and it compares the output of the pass tube to the referece voltage and sends correction to the pass tube as needed to eliminate Mains noise and voltage fluctuations. The WV uses a 6JC6A In this location and you can also use other 9PM based tubes like the 6HM6, 6HT6, 6JD6, and 6KT6. The samples of these tubes that I've listened to all sound fairly similar.
Finally, all voltage regulators need a voltage reference and the gas-filled 5651A/WA Voltage Reference Tube (V8) is the best-sounding voltage reference ever made, period. Zener diodes, band-gap references, or other gas discharge tubes don't even come close in terms of sound quality. In this location you can also use a 5651 or a 5651WA.
Note: Tube-basing terms like 9EU and 9PM refer to EIA/RETMA designations for how a tube is wired to its pins. Two different tube types with the same tube-basing might be equivalent tubes if they are electrically similar. Electrically-similar tubes with different basings cannot be substituted for each other.
Vendors of good tubes include The Tube Depot, Upscale Audio, Vintage Tube Services, Vacuum Tube Valley, thetubestore.com, and Antique Electronic Supply.