has anyone else experience this.....

There is something wrong with the tubes, (they might just be
worn out? How used is used?) or your cj PV-10 just doesn't
play well with them or you just don't like them. Maybe time
to move on.

Sorry, but what you describe, isn't what I have found to be
true with NOS Mullards. I have been using these tubes for
over 30 years and still have bunches of them left. By far
"my" favorite tube, but definitely not for
everyone. As always, YMMV...

You may also have FAKE Mullard tubes. Any tube which is considered classic is going to have fakes being sold. New cheap tubes with phoney markings..

that's what I think as well, actually they blew out my preamp, repair guy said it blew a resistor, was pulling 6amps which it should not have.............

I agree with Al, that NOS should mean the tube has not been used in anyway whatsoever, however this is usually not true in so many cases.

Here are a couple of good articles by Brent Jessee about NOS tubes,

NOS Tubes: New Old Stock or Nasty Old Stuff?

A BRIEF NOTE ABOUT NEW OLD STOCK TUBES

Brent Jesse is a very reliable seller, but IMHO, some of the NOS tubes may possibly be slightly used, however do exceed rigorous testing for NOS. I have read many times that even a good slightly used old tube can still be much better than some of the new production junk. The problem lies with everyone acquiring old tubes calling them NOS regardless of the condition..

I used to questioned NOS tubes that did not come in original box, however found out that this means nothing. A poor used tube can easily be place in an original box. The box of a NOS tube may have deteriorated over years. Also, I have some very rare NOS Brimar black plate 12AT7's from 1955 that came in a bulk pack of 100, so no individual box, however, I do have the original bulk box.

Elizabeth also brings up a good point about tubes being relabeled, so it is important to know the physical characteristics of the internal structure for a particular tube.

It is always best to purchase from a reliable seller that offers a guarantee.

I normally get my tubes from andy of vintage tube, put had been calling around talking with some of the other pundits selling tubes and got burned so to speak...