12AU7 and 12AX7 long black plates vs short black plates. Any difference ?

Hi we all talk and discuss the different subtle sometimes labelled subjective characteristics of various tubes and audio equipment in general? Aside from the obvious frequency response, noise and tube related std measures does anyone know of how these can be measured? For example subtlty, detail and naunce. Also “warmth and snap” and the so called “weight” tubes and sometimes electronic equipment add to music reproduction?

Thx

OP

in my humble opinion, I do notice that the long black plates have a more 3D sounding result with more vibrance and detail/ the short plates or may I add, the gray looking plates do not deliver the same sound or musical effect that i hear from the LONG plates.

I have both long and short and the black vs the gray. these are 12au7 and 12ax7 tubes of Tele, MULLARD and Sylvania manufacture. I notice that they are most sensitive when they are on my LTA preamp and the gain stage on my 845 audio note clones

this is just my observations and YMMV 

joeycastillo, yes, it appears to be a consensus here that long black plates, both 12AU7 and 12AX7, are overall better sounding, regardless of particular equipment. They deliver the most authentic sound.

When it comes to military/industrial substitutes for them the picture might be a little less clear. I intend to try Sylvania 5814A triple mica and perhaps RCA 5814A triple mica at some point. Other than that there is probably no reason for me to try anything else.

@inna 

"12AU7 and 12AX7 long black plates vs short black plates. Any difference ?"

Microphonics. @mulveling goes on about it -

"Bigger plates can mean more microphony too, though. The way these things are suspended in the glass envelope makes them a vibration antenna, and the mica spacers have to retain a tight grip over all these years & heat/cool cycles."

@mulveling 

"And with a tube power amp or integrated, the vast majority of heater draw is from the power tubes. You're getting into a fractional % of a delta on the filament tap from this."

To elaborate -

The small signal tube heater supplies AC or DC are taken from a separate winding on the power transformer and in the case of DC a separate rectifier bridge and ancillary components to present clean power to the filaments at 6 or 12 volts.

Hi Joecastillo, i also concur - just wish we had measurements to demonstrate this, ie 3s soundstage, musicality etc.