@nonoise , thanks. Brent is one of my go-to-guys and he describes the tubes pretty well, but his prices for Brimars seem very high.
Here is a CV4004 boxplate, but don’t know anything about the dealer...
https://www.kcanostubes.com/content/nos-brimar-12ax7cv4004This is a CV492 with same plates as a CV4004. But much cheaper than CV4004’s...
https://www.ebay.com/itm/True-NOS-Vintage-Brimar-CV492-Mil-Spec-12AX7-Long-Gray-Box-Plate-Vacuum-Tub...Here is a 6057 that the dealer states is the same as a CV4004,
but Brent says... "One of the rarest Brimar made 12AX7 tubes is this long plate with the famous Yellow T decal on the glass. These are all the older long plate version that is so difficult to find today."
And to make it more confusing, the "T" is not yellow.
https://tubeworldexpress.com/products/copy-of-6057-cv4004-mullard-rebranded-brimar-t-nos-1981-gm-160...I’m wondering if many of these tubes are being re-branded. The safe bet would be to go with Brent, but first I’m hoping one of our members knows some Brimar history.