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

@inna Yes, I thought so and is why I passed along my own observations over the last 20 plus years. My main source of info in the beginning was Joe's Tube Lore and I agreed with most of anything that he ever had to say. I was surprised to learn that Joe based all of his opinions on CD listening and I based mine on vinyl listening. Just kind of an interesting sidenote. 

I would always use analogue source to compare anything.

Anyway, it is good that in the age of AI and streaming we are going into detailed discussion about vintage tubes.

There is a set of three Sylvania 5814A triple mica NOS for $150 on ebay right now, if anyone wants to try them. I'll pass, need resources for Mullards XF2.

@billpete 

Mine aren't gold pin. I don't know a lot about tubes.

@slaw I'm not claiming to know a great deal about them either but I have been enjoying them for about the last 25 years or so. I would guess that the non gold pin Sylvanias would not sound as good as the 3 mica Gold Pins as they were their "top of the line" and have commanded pretty high prices over the last 20 plus years. I used to buy them for $15 to $30 apiece back when I started buying them. I bought NOS and lightly used ones at those prices. You'll be hard pressed to find any Sylvania Gold Pins for less than $80 to $150 now, with 3 micas bringing the highest prices. Must be something to it. I never had any Sylvania 5751's that were not gold pins. I do have others, like 5814A's in steel pins and they are fine but I imagine if you found the same in a gold pin, it would be even better. I don't think it's so much the pins themselves that make them better (although it can't hurt) but what went into the rest of the tube as well that made them a premium tube. My 2c.