isolating a tube problem - ARC LS5 preamp

Well, the ARC LS5 could be what, 10 years old or more? Maybe it's more than one tube that's bad. I would replace them all - and I would have done so at the time of purchase. Those tubes are everything - makes no sense to skimp. Might be time to invest in a tube tester.

The easiest way, since you've got a noisy tube in one channel (which you almost certainly do), is to switch the tubes between the channels in pairs, one pair at a time, until the offending bits move -- and there's your bad apple. That said, I tend to agree that, since you can't know the age of any of the tubes and any (or many) of them could be loosing steam (whether they are being noisy about it or not), it might be a good idea to seriously consider re-tubing the whole thing. You may find your sound drastically improved across the boards, and the only way to know for sure is to try it. You’ll need new tubes eventually anyway, it’s always nice to have extra ones on hand, and, simply enough, that’s the worst that could happen by trying – you might end up with a few extra...

I cast my vote for tube rolling. When I replaced the Sovtecs in my ARC preamp, I was amazed at the improvement in imaging, subtle inner detail, transparency and dynamics. What to replace the Sovtecs with? After experimenting with several different types of 6DJ8s, I found that my unit sounded best with a combination of Siemens 7308/E188CC w/gold pins and either the Amperex 6922 PQ w/gold pins or the rare German-made Amperex 6DJ8 Orange globe logo w/steel pins. I found the Dutch Orange globes to be a bit too analytical in my preamp, but sound great in my ARC amp. The Amperex Bugle Boys and A-Frames are perhaps 90% as musical and detailed as their premium brothers at about half the price. Ditto for the Siemens 6922/ECC88 w/gold pins.
It's easy to understand why ARC had to go with a reliable, easily-replacable tube. However, you can do much better.

looks like the tubes are getting noisier and most of the tubes I've ordered have not arrived yet. Should I stop using the unit till the rest of the tubes arrive. SHould I unplug everything to swap out a tube or is a simple off on the power strip sufficient to change out tubes?

Thanks

Tom

I changed out six of 10 tubes, more to arrive

wow, what a difference, all the musicality of the preamp is back and more and in spades. Guess I'd been slowly lulled to sleep as the tubes went bad. Siemen's E88's and Valvo E188's sound pretty nice, need to add that expensive telefunken next.