First Tube Amp: Advice? Keep spare tubes on hand?

I don't know how your amp is setup to bias; it maybe a tube at a time or pairs or quads; I would talk to the manufacturer and tell them what you are measuring;then go from there.
If this were my amp I would move tubes from left to right channels to see if the measurements move or change;also inspect the pins on the tubes for oxidation;could be some buildup that needs cleaning as well as the tube sockets themselves.

Again, thank you all mucho.
I have spoken to the manufacturer and they are sending me a shipping label to return this one and are sending me another.

Is there a priority on what spare tubes to get first or to keep around? I got a modified Baldwin amp that I believe came from an organ. It consists of the following tubes.

3 12AU7 tubes 1 labeled Baldwin 2 Electro Harmonix
2 Harmon Kardon 7408 tubes
2 Baldwin 6L6GB tubes
1 Baldwin 54UGB tube

I've been listening to it for quite a bit now and I really like the sound it makes. Lots of subtle details have come out in various music I've been listening to. It isn't as forward as some SS amps I have. The previous owner said the tubes that it came with tested well but he didn't know the amount of hours total were on the tubes. I'd like to get the exact same versions of the tubes I currently have on the amp because I'm not exactly sure how to rebias the thing. I've priced out these tubes from Brent Jessee and it is getting bit pricey for me which is why I'm thinking about getting a couple of the necessary spares first.

Thanks in advance for the advise.

If it's a manual bias you need to know how to bias them first and formost. Only because I have never owned a tube that didn't need biasing after replacement. No matter what tube I 'roll' including input and driver tubes I always start at min bias to let them all warm up first (about 1/2 hr). Then I bias them low and check the bias every 1/2 hr or so. Then I check again on a daily basis for the next few days. I have seen tubes take several days to settle down and stay properly biased.

That being said I will admit that 'factory' matched tubes can be very poorly matched. Something I learned from Jim McShane when I bought some GL KT88's and SED EL34's. I brought my 'factory' matched EL34's to Jim and he showed me how far away they were from a 'good' match.

Good Luck

Xti16 I couldn't agree more. Running an output tube on a machine for 10-15 mins. is a waste of time. Many output tubes require 24 hrs. for the innards to stabilize. I just got done installing new output EL-34's in a Conrad Johnson Amp. And sure enough with brand new tested tubes one of the Wing C EL-34's started to run away.... You have to be vigilante.