I have four Western Electric 249B mercury vapor half wave (diode) rectifiers available. There are 3 of the earlier engraved base tubes, and one with a printed base. These have a UX-4 base. The heater uses pins #1 & #4, and the plate connection is on the cap. I tested these on my Hickok 533A using the settings for an 866A tube. I let them warm up for a good 20 minutes each before applying anode voltage, and they all test great! These do require a short pre-heat time before each use (about a minute), and a long pre-heat after being handled, etc.
If you want to build the ultimate power supply, these will surely get you there. They have a very cool blue glow that fluctuates with modulation. Beyond any 866A. I've attached a link to the Western Electric specification sheet up top. Please, just know what they are, and how to respect them.
I'm asking $200 each for the earlier engraved ones, and $180 for the printed base tube.
These will be very well packed, and shipping within the contiguous states will be a flat $20 charge. I will only ship these to continental US locations. PayPal is my preferred method of payment, and at no extra charge (the "Friends and Family" option is appreciated, but not necessary). I will also accept a M.O. through the mail.
Let me know if you have any questions, and thanks for looking!