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Guitar chord forum - chordie → Guitars and accessories → QUESTION ABOUT TUBES
I looked back several screens to see if this had ever been raised and couldn't find anything.
Are there any symptoms to listen for, when an amp's tubes are going? Or do they just quit? Is there anything I'd be able to look for just by giving them a visual check? Everything seems to be working okay in my Peavey, but it's just something I'd been wondering about. If it's any help, it has 3 - 12AX7's and 4 - 6L6GC's in it.
Any help would be appreciated!
Hello, Lacaca ... welcome to Chordie!
I have a Peavey ValveKing212 which has the same tube setup as yours, and I re-tubed it a couple of years ago. My symptom was a high pitched squeal which would come out the amp once in a while, even though it wasn't very loud. The tech at a local music store suggested some things:
Pre Amp Tubes (6L6's)
- he said that when the pre-amp tubes start to go, there will typically be clicks, squeals, crackling, fuzziness, etc.
- If it's just one bad tube it will usually be glowing less than the good tubes.
- he also said a person can also gently tap each tube one by one, using something that doesn't conduct electricity (like a paint stir stick, plastic utensil, etc.) while the amp is on. A bad tube will react to this in a way which you will hear
I just replaced all 4 of the 6L6's at that time, and the problem was solved.
Power Amp Tubes (12AX7's)
The power tubes (12AX7's) will show trouble by a noticeable drop in power, and usually glow more of a deep red color than usual. If they're really bad, the amp will over-heat, and the on-board fuse will blow. These tend to wear out faster if the player is loading them heavy on the front end, with overdrive pedals, active pickups, etc. Here's a pretty good link that describes these things better than I did ... I hope this all helpful:
High pitched whistling, crackle, reduced output and generally less impressive sound quality are what I listen for. 
EDIT:
After additional thought, here's the decision tree I use:
- Does the noise happen with multiple cables?
- Does the noise happen with multiple guitars?
- Does it happen when you bypass pedals and effects?
(If the answer is "no" to either question, it's probably not the tubes.)
- Does the noise happen when you turn dials or wiggle your cable whilst it's plugged into the amp?
(If yes, it's likely not the tubes.)
- Does it get worse as your amp heats up?
- Can you hear it even when your guitar volume is rolled to zero?
(If yes, it may be the tubes.)
Guitar chord forum - chordie → Guitars and accessories → QUESTION ABOUT TUBES
