Here’s something completely different from Russia. Electro Harmonix has released the all-new EH 7025 Tube and it’s quite a departure from their previous 12AX7 offering. Clearly this was new from the ground up and not a re-working of something else. The only thing that carries over from their other designs is the rather tubby bottle they fit into. This 12AX7 is a dual triode vacuum tube with very short plates, in fact the plates are open at both ends so you can see the cathodes and control grids quite easily. There has been a lot of effort to shield the triode sections, including a full plate between them to prevent interference and added support across the two triodes to cut down on vibration. A single overhead getter bridged across the triodes tops it off. The micas are not extra thick but they are clean and well aligned to hold the structure. Overall the tube is well built with good alignment of the internal structures.
How about the sound? Well they are advertising this as a 7025 amplifier tube. Back in the day this meant something. To be specific, it should indicate this tube as having been designed for extra low noise and microphonics. EH has obviously used this as their main design criteria and really hit the mark. It’s quiet and I could find no trace of microphonics in a couple demanding guitar amps and my tube phono stage.
Tonally they are balanced and smooth. No harshness in the top end. To my ears these tubes seem to have a bit less gain than a Tung-Sol 12AX7 Tube or the JJ Frame Grid.
Guitar amps is where these guys will shine. Regardless of your taste, from high-gain to folk, these will be great in your amp. Almost no background noise allows the high gain user to really drive the amp hard and be assured that the only feedback will be by design. At more reasonable gain levels you will find these to be warm and detailed.
Only time will tell how these perform after a few hundred hours of use, but out of the box they seem to be an excellent tube at a good price.