[youRobert]

gotten hopelessly addicted to the machine.  first thing i started to do was explore tubes, if only for back up should catastrophe strike.  i think i'm finally calmed down, but still wondering whether there is a better 12B4A than the JAN GE that the Good Doctor is shipping now?  only one of the 'net dealers identifies their 12B4A stock as JAN GE, so there is a source that doesn't deplete the Doctor's stock.  if it really doesn't matter, i'll just get a couple of them call it a day.

[dpump]

The 12B4A tubes don't make as much difference as the 5751. I found that a RCA Command 5751 and a Raytheon triple-plate 5751 made a big improvement over the stock tube. Upgrading the power supply diodes to Hexfreds also made a noticeable improvement. Replacing the capacitors with 4- Blackgates and 2-Auricaps makes a small improvement. Finally, replacing the filter caps with larger values cuts down on the hum a little and tightens the bass.
   If you can do these upgrades yourself, the price is pretty reasonable. But, go for the 5751 replacement tube first.

[youRobert]

my Ear+ is the almost HD; cap upgrades and Noble pot.  i got two RCA 5751, from the 60's. a WA and a JRC.  both sound better than with the Sovtek.  a Sylvania gold pin and GE triple plate are on the way.  guess i'll have plenty to test with.  

the conclusion is that the Doctor is right:  any North American NOS 12B4A will do.  given how lightly stressed the tube is, this does start to make sense.

thanks.

[dpump]

Glad to hear you have the cap upgrades. They are worthwhile. If you can get the Hexfreds in, I think you will find the bass improvement will be worth it, especially if you are using Grados. Enjoy.