How do you know when to swap power tubes?

[mindwave_21]

I own a Traynor YCV40, never changed any of the tubes out, and I've owned it for about a year. I never really turned it up, but a buddy and I are about to do a gig for the first time, and I've turned the volume up to about 3-4 (that's loud enough to have to wear earplugs inside the house). Well anyways, I was messing around with it today and towards the end of my little practice, I heard the amp start to fizz in and out. It sounded like a scratchy pot on the Strat copy I have, but I realized I wasn't playing that guitar, but my new h535 which doesn't have those problems. Plus, I wasn't touching the knobs. Anyways, I wanted to know if this was what the tubes due when they are about to die or if this was circuitry, because the gig is this thursday and I have no replacement tubes on hand.
I was thinking of going to GC tomorrow to get some 6l6gc's (I think they sell Ruby tubes, but I'm not sure).
Thanks for the help!

 

[Farview]

That sound is usually not the tubes, it could be a bad jack. If you put something in th fx loop and recently took it out, the jack in the fx loop is bad. To fix this just plug a short cord into the fx send and return.
To answer your other question, you know its time to change your tubes when the amp sounds mushy and muddy compared to what it sounded like before. I used to be able to tell by where my presence control was. When the tubes were new, the amp would sound right to me with the presence on 5 or 6, when the control got to 10 it was time to start thinking about new tubes. Don't forget the preamp tubes.

 

[mindwave_21]

Thanks for the reply. Actually I was playing with no fx and I've never actually used the fx loop because I don't know which effects to put in there. I guess it could have been the cable as it was a little twisted up the way it was. Hopefully it won't happen again.

 

[fretmeister]

If it happens again you should try replacing the power tubes. I've heard that fizzling before and the power tubes were the culprit. Wierd noises and microphonics is another sign of tube malfunction. If they don't fix the problem, then keep them for when you need them. I think the preamp tubes outlast the power tubes so you don't necessarily change them when you change power tubes, but maybe someone more expert than me has some guidelines.

 

[mindwave_21]

Thanks guys. Haven't had problems with it recently, so I'm going to cross my fingers. Just ordered some JJ 6l6gc's online and they'll be here by next week, but the gig is in 2 days. It's alright, I think for the time being I'll leave them in. I went to GC and they only sell Groove Tubes and Boogie, and as we all know, they're just re-labled Svetlana/Sovtek/JJ Tesla tubes that are marked up, so I decided not to pay $45 for a pair and got them for $28 instead...I don't think they'll arrive in time for the performance though, but we're playing a very small gig with only 4 songs, so it should be alright.

edit:
I have not heard any muddiness in my amp at all, so I'm wondering if the tubes were actually the problem. It only happened once, and I practiced at pretty loud levels the day after and everything was alright. Does autobias keep the tubes from getting muddy near the end of their life?

 

[Hard2Hear]

You can usually see tubes going out if you look at them. If the color looks off, or if they geet bright and dim back and forth they are going. Power tubes are goofy and can do lots of things before going out. From just plain losing volume and quitting to a full fledged explosion. I've had both.

H2H

 

[Toki987]

When my tube amps would start buzzing and crackling I'd bang the amp on the top with my fist and make sure the tubes were seated good afterrwards. When that wouldn`t work any more I'd replace them. The 4 6l6`s in one of my amps are from '78 and still sound good.

 

[donkeystyle]

groove tubes makes their own tubes now. ...the make 6l6's and i believe they also make el34's now.

 

[donkeystyle]

it appears i was wrong about the el34's. i read on some website that they do, but their website doesn't say they do. they dont say they dont, but it's pretty apparent that they only make 6l6's.