When I first looked at these Tungsram ECC83 amplifier tubes I thought of vintage Mullards. I don’t know if they were using the old Mullard equipment to build them or if they were just trying to copy the look and feel.
These are vintage all the way. The bottles are the correct size with a fairly flat top with 4 seems that you can detect. Large grey ribbed plates topped off with a large round getter ring supported from both sides of the plate structure. The Mica supports are medium thickness with a dozen contact spots around the bottle. There are dual support rods between the top and bottom supports to minimize microphonics.
The vintage Tungsram 12AX7 vacuum tube are not bright and sparkly tubes. I find them to be a bit darker than most current production vacuum tubes, but not deficient in any way. There’s plenty of high end, it’s just not as aggressive as many are these days. At the other end of the sonic spectrum the amplifier tube has great bass definition, very solid and focused. This was very apparent when using them in my phono amp where the soundstage seemed to open up with depth and clarity. The midrange was nicely balanced and I couldn’t detect any hot spots when listening to a variety of material. Due to the large plates there’s lots of gain on tap.
If you really wanted NOS Mullard 12AX7 tubes but can’t find/afford it, these would be an excellent substitute. Beautiful, balanced reproduction in an old school design that’s still available if you want it.