4BZ6 (white & red). New in Box (NOS). We have hundreds of thousands of tubes for manufacturing purposes, all vintage american made. 2 If you are looking to re-tube and amplifier, guitar amplifier, preamplifier, compressor, equalizer, microphones or any tube equipment, send us the model number and we will take care of the rest, and generate a custom listing for you. 4 We carry most USA made brands such as RCA, GE (General Electric), Sylvania, Raytheon, TungSol and PentaLabs , just to name a few. 5 We also carry european brands such as Amperex, Mullard, Telefunken and Marconi , just to name a few but in less quantities.