How do I know when to replace Melos SHA - 1 Tubes

I purchased a used Melos SHA-1 Pre-Amp over 5 yrs. ago, since then I have upgraded my Amplifier replacing the Rotel with the ARC VT 100 MKII..How can I tell if my tubes need t be replaced? I do listen to quite a bit of vinyl & I'm using the McCormick Phono Pre Amp. Should get a new PreAmp? Is there a Pre Amp that will work well with the ARC Amp which has a phono stage..Or should I continue using the Melos? How much for new Tubes; which tubes & where can I find them?
The rest of my equiptment is:
ProAc 2.5 Speakers
Meridian 518.20 CD player
PS Audio P300 Power Plant
Call Kevin Deal at Upscale Audio for a tube recommendation. The SHA has only two tubes in it as I recall, so replacing them or even upgrading to something fancier should be inexpensive and potentially rewarding. You could upgrade premaps, but the SHA is certainly a fine preamp.
I own a sha one. I will never part with it.Four 6922 tubes every 5000 hours.
It would be helpful if you said what tubes are currently in your Melos -- to give some idea of what you're hearing right now ;--)

That said, any matching pair of Amperex or Siemens 6DJ8's that say "Made in Holland" and have four ridges in the glass on the top (radiating out from the nipple) will guarantee authenticity. This includes the famous Amperex Bugle Boys and Orange Globes, but you pay for those logos! Look for Amperex or Siemens 6DJ8's rebranded for OEM users, for example, these I just bought (stole ;--) this pair on eBay that are branded Hewlett Packard, for $16, free ship! Compared to $130 for the EXACT SAME THING from Upscale Audio!
Don't be afraid of eBay. Kevin's stuff is OK, and guaranteed, BUT his NOS tubes are usually 5 to 10 times more than you'll pay privately or on eBay, AND they are often BARELY above minimum specs. Then, on top of everything else, you have to read Kevin's flowery descriptions (please! gag me with a spoon ;--) I know all this because early in my eBay purchasing, before I started asking for test results, I wound up a few times with Upscale tubes the sellers probably just wanted to unload. Or I bought tubes on eBay where photos of the tube boxes would have shown the Upscale sticker, now a deal-breaker for me; whereas the ones I just got for $16 really are N(new)OS!

BTW, my 'cheap' NOS eBay Amperexes replaced some beautiful new Sovtek 6922's that the seller included with my SHA-1, and of course they sounded like . . . well . . ordinary ;~)
Brad, four tubes?! I hope you're not serious . . . . or I've been swindled!~

"How can I tell if my tubes need to be replaced? "

If you hear excessive hiss, hum or microphony, replace the tubes.

Also, if there is a noticeable channel imbalance, you should consider replacing the tubes.

To 100% sure, swap the tubes between channels. If the noise or imbalance follows the tube, Bingo.

There is another reason for changing tubes: lack of dynamics and less bass punch, a sign of weak tubes. Unfortunately the only way to find out is by swapping in a new pair of tubes (NOS or new production) that are matched and measure very close to 100%.

I agree with the above NOS recommendations and would like to add the king of the hill (IMO): Amperex USN-CEP gold pin 7308, a super-quiet and matched-section 6922 developed for Sonar applications.
The equivalent european tube is Philips Netherlands E188cc, I believe developed for the professional Studer reel-to-reel recorders.
Have fun!
Casouza, thanks for the tip on those Amperex/Philips tubes! Probably impossible to find, right?
You'll never really know for sure, it'll just always be in the back of your head, distracting and gnawing at you. The seeds of a conspiracy planted to induce paranoia, overtake your senses, and the world as you previously knew it.....or thought you knew it?

:-)Just kidding!...............................or am I? :-)
Casouza, I guess they're easier to find than I thought. But do I want to spend $300!
Nsgarch, no need to pay U$ 300
Try Upscale Audio Gold Grade tubes.
Best wishes