I buy mine from Bob @ Eurotubes. Every time I get them for other sources I have a high failure rate. When I get them from Bob, he weeds out the bad ones in advance.
If I don't get them from Bob (and I have) I get a 25-50% reject rate, with Bob, I've had ONE bad tube, which he promptly replaced for free including the shipping charges and didn't ask me to send the bad one back.
Yeah, it costs $2 more per tube, but you'll spend more than that on each tube plus the hassle, so I'd rather buy them from Bob. Here's his site for those interested.
I've used 200 JJ's in the last three months and not had any failures.
However I buy them pre-selected and tested from a reknown wholesale distributor. If you were to get a batch straight from the factory the failure rate would be somewhere between 30-60% depending on the batch.
I have very good luck with the JJs ECC83s ...I buy mine from Revolution Guitar and haven't had one go bad yet. I have not tried the ECC803s but Glassman did a shoot out with clips of several different 12AX7s and IMOP the ECC803s was one of the better sounding tubes, even compared to some of the NOS tubes, but I cannot speak for its reliability
I've had nothing but good luck with them. I get them by the dozen from Antique Electronics, who doesn't do much in the way of QC (I believe), unless they pay JJ extra to sort them ahead of time. I've not gotten any bad ones yet. I did have a couple bad AU7's a coupla years ago, but not since.
I go through quite a few building amps, but the JJ's have always been VERY reliable for me.
Actually, in my D/13 RSA 23, I purchsed a new set of JJ KT88 power tubes from Bob at Eurotubes (these babies are expensive anyways) and I noticed that the tubes were SUPER loose when I placed them in. Is that really bad? Maybe not getting enough contact to the pins or could the pins be too small?
I've sold hundreds of JJECC83 and had very few problems with them. Far less than any other brand.
As for power tubes, yes the pins are too small. You need fresh sockets or you need to tighten the sockets to make them stay connected. This does not apply to their 9 pin tubes. However, JJ is starting to release some power tubes with bigger pins now. I just received a new batch of JJ 6L6 and the pins are bigger and fit the sockets much better.
I also retention the power tube sockets as described in EuroBOB's included info sheet (he sends with every set). if the tubes are loose in the sockets you may experience HV arcing! retention sockets asap!
I have used JJ preamp tubes from Bob and I havent had a failed tube yet over the past years. Lke others here, I have installed them in many many different types of amps. I recommend them.
Electroid, glad to hear they started using bigger pins! that would be a very good move.