"Welcome to a world of numbers. A world where one false step can lead to a fall into an abyss... "... alright, I can only go so long trying to emulate Rod Serling. Did you know that in the world of Tube Amps, an EL34 is the same thing as a 6CA7? Did you know that my Groove Tubes™ 6CA7's are also marked as GTE34LS's? Groove Tubes also seem to be 'chubbier' in size, compared to the stock/oldstock EL34's I also have, so size (apparently) is not necessarily a good guide to matching tubes. I noticed one of my power tubes (an EL34/6CA7/GTE34LS) was giving off a metallic buzz when I cranked up my distortion on my Louis Electric KR12. (I spoke to Louis today.. he is great to talk to). One thing I found out was that it is not that uncommon to have tubes that are microphonic. Whether you want to change them out, and not put up with the buzzing seems to be up to you. My boxes of Phillips™ EL34's (two of them, plus one labelled GZ34, which comes in the same box, but is a different tube) came with a giant warning "REMEMBER-YOUR AMP MUST BE REBIASED BEFORE INSTALLING YOUR NEW POWER TUBES TO AVOID PERMANENTLY DAMAGING THE TUBES". Whenever I hear those two words... "PERMANENTLY" AND "DAMAGED" I get worried... and so should you. My Dad used to own an old amp from the 1950's, and I remember as a kid, whenever one of those little tubes got too dark, and didn't give off that mellow amber glow anymore, we would go through a big box of tubes, and I would help him find the one we needed... then we would just plug her in.
Don't do that (with your power tubes). Spend the few dollars to take your high-end beloved tube amp (and any spare new tubes...) to a professional who can make sure that amp is rebiased... and save yourself spending more than the small fee he or she is going to charge you...
