How often should I replace the 12AX7 preamp tubes? I play about 4-5 hours/day (average).

Thanks!

You should replace them when they are dead. *There is no set rule for how long they last, but in general, they last longer than power tubes. *Maybe twice as long or better life expectancy for power tubes. *They are also self-biasing of course, so don't be afraid to change them yourself.

You'll be able to hear them starting to go bad. *They will go 'microphonic'. A high pitched whistling occurs.

Well, I guess I'll post by bi weekly tube wrap up.
Good brands=GE, RCA, Westing House, Svetlana, Amperex, Telefunken, Sylvania, Tesla, JJ
If you see anything else, and it's marked JAN, it will be top notch. JAN stands for Joint Army Navy, tough tubes.

Not so good brands=Sovtek, anything made in China, (newer) Fender, Groove Tubes. Fender tubes made from about 95-00 are Sovteks, the ones made for the past year or so are Groove Tubes. Groove Tubes basically takes tubes from various brands and matches them and tests them, then they charge double the price.

Your best bet is to buy from your local amp shop, they usually have a decent supply of tested tubes on hand.
alt.guitar.amps for more info. Pay attention to the posts by Lord Valve. That guy really knows his stuff.

On that note, some tubes are not suited for guitar amplifiers. *The EI Yugoslavia is supposedly a high quality audio tube but not for use in guitar amps...goes microphonic very easily...so read about a tube's specs before you get it.

Doink- Lord Valve does know his tubes, but seems more concerned with that newsgroup than repairing gear in his shop (NBS Electronics, Denver, CO). *

Example:
My buddy Jason took his old-school Echoplex into NBS for repair. *We stop back 3 mos. later, not done. *6 mos. later we pop in the shop and it hadn't moved. *The other pieces of gear in his shop with repair tags had more dust on them than the guestbook on ER's site. *It was truly depressing. *He may know his tubes, but I wouldn't drop off my gear there for any kind of timely repair.

My favorite power tubes: *Svetlana EL-34
My favorite preamp tubes: *Tesla/JJ 12ax7a's

Check out:
http://www.thetubestore.com

I have NOS Telefunkens in my pre-amp. You can't believe the tone. And it is really tough to get the suckers to feedback.... the best investment in tone that I have made.

Dave

dammit, I love EL-34 tubes. *Nice big, warm, round sound and are they loud! *If I had money buning a hole in my wallet I would buy to quartets of Mullard EL-34s.