Beautiful NOS matching pair of very rare, special application, low noise grade RCA grey glass VT-231. These are unused stock from a collection of industrial grade electronics I recently acquired. They have orange stamps on the tops and were selected out of many VT-231's for low noise and close triode matching.
They also have matching date/plant codes on base. They come in old white military boxes they were re-boxed in after testing.
They have been listening tested in a high resolution system and sound excellent!
About as nice a pair of these as you will find anywhere.
Fully tested on a calibrated Hickok 539C at 2700/2725 & 2850/2850.
Please see my other items for some more tubes from this collection of top quality