If you were a tube preamplifier manufacturer

Mr S- Actually, the cost of their ECC88 exceeds that of the pre-68, NOS Siemens CCa by 25 to 50 dollars(right now, for a very close triode balance, high transconductance reading CCa). I still prefer the CCa, as I feel it has a more accurate rendering of the original soundstage. Their team has been largely successful though, in their goal to reproduce(as authentically as possible) the sounds of live music(ala Siemens/Telefunken), rather than the classic "warmer" tube sound(say- Mullard/Brimar/Ediswan). If one prefers euphonics, the EAT tubes will not sate their aural palate. I've not heard the EAT ECC803S(compared say to the Telefunken of the same designation), but given the Euro Audio Team's goals- I'd have to assume it would possess the same flavorings(or lack thereof).

I'd be broke.

I have experimented with Mullards, Bugle Boys, and have found that a lot of hype is involved with these tubes. They can sound really spectacular in some situations, but not many. I have gotten the best sound with 12AX7, 12AU7 from Ei, and Chinese tubes. Unfortunately, the Chinese tubes do not last very long, 300 hrs or so. The old tubes NOS do last longer, but I find some a bit colored. The Chinese tubes are clean, dynamic, (You have to get the very low noise versions) and very big sounding, but a lot of them are noisy and the short life....no perfect tube. The new Mullard and Tung Sol, and the Sovtek, Winged C are very good. NOS does not mean all the rest are junk. They have their place, just like vinyl....all records don't sound great, but some are great.

you can design tube circuits so that they are relatively insensitive to changes in tube manufacturers.

i would prefer to allow for variation in sound from changes in tubes. i would not use any current tube in my circuit. sorry, i would insist on using a nos tube. i would use a 6cg7 or two in the line section and a 5ar4 as the rectifier.

As a manufacturer, you have to consider the lifespan of the product itself. Any decently built amp or preamp is going to last at least 20 years. At the end of that time, where are you going to find the tubes? One thing is certain- if you built the initial design to only work with a certain NOS tube from the get go, you have saddled the customer with a curse. At the end of 20 years, how common is an NOS type going to be if it was only available NOS 20 years earlier??

Of course you cannot predict what conditions are going to exist in the tube market 20 years in advance! But its a good bet that a tube that is not in production now is going to be a lot harder to find in 20 years.

IMO it is unethical to design a tube product that only works with NOS tubes.