Tube question

[DarEch]

I have a bugera 333xl, first tube amp Ive owned. Got a couple questions Im hoping you guys could help with:
1. How do I know when its time to change the power and or pre-amp tubes?
2. After replacing these tubes, should I "wear em in" by leaving the power on for a period of time?
3. Wanting really strong gain, what pre-amp and or power amp tubes would you recommend?

Thanks

[Enzo]

Power tubes
If as tube fails, replace it. They can fail in numerous ways.
Over time they go dull, like guitar strings. Dead strings still work, but they sound dull and lifeless. Same deal with powr tubes. It won't be here today, gone tomorrow, it is a gradual loss of tone. Eventually, like strings, you just have to decide it is time for fresh ones. I almost always replace the power tubes as a set.

Preamp tubes
Power tubes wear out doing their job. Preamp tubes can last for decades, they don;t wear out in the same manner.
Preamp tubes can fail, and if one does, replace it. No need to replace the whole "set" of preamp tubes.
Preamp tubes can stop working completely, or they can get noisy, or get microphonic, and other problems can happen.

No need to warm up new tubes any different from warming up the old ones. They are ready to play when you get them.

That amp is plenty loud and gainy to me. Different preamp tubes can make a tonal difference, but the amp will always sound like what it is. Differences will be relatively subtle. Tone is subjective. You can try different tubes in the amp and see what you like. Each socket does a different job, so again, the preamp tubes are not a set. You can have a row of all different brand preamp tubes if you like, or all the same. Up to you. A tube you like in the first socket may not please you in the second socket.

[Chuck H]

1. How do I know when its time to change the power and or pre-amp tubes?

If the tone CHANGES by to losing power, bass definition and/or clarity this could mean that it needs new power tubes. It's best to check the tubes for a gross mismatch, proper bias and output power to help determine if you should replace them. Eventually you will just 'know' by listening that the power tubes are tired.

Preamp tubes can do similar things, but instead of a loss of power it would be a loss of gain. Also, preamp tubes can become microphonic and begin to squeal when higher gain settings are used. Preamp tubes should last many times longer than power tubes.

2. After replacing these tubes, should I "wear em in" by leaving the power on for a period of time?

No. Just be sure the bias is set correctly when you replace power tubes. Some preamp tubes do "wear in' making occasional pop, fitz or hiss noises that SHOULD stop after a day or two. But not burning the tubes in won't hurt anything. Just plug and go.

3. Wanting really strong gain, what pre-amp and or power amp tubes would you recommend?

Whatever the amp came with stock. That is, as far as the tube # designations. almost all modern tube guitar amps use 12ax7 type preamp tubes. This is already the highest gain tube 'type' for the job. Many MFG's 12ax7's have other designations after the tube # like A, WA, WS, LPS, etc. These all mean something to the MFG and different type 12ax7's do sound different and gain is somewhat variable. By reading descriptions by sellers you'll be ble to get an idea what to expect from a specific tube. Also, look up tube reviews on line.

Power tubes can also alter the distortion level, but only if you play the amp loud enough to make them distort. different models of the same power tube from different MFG's can have different current characteristics. Some will saturate sooner than others giving more distortion. This usually means fewer CLEAN watts though. So if a loud clean tone is also important you need to make a compromise. Since most modern "super crunch ultra blister crack two bricks together" amps generate a ton of preamp gain they usually arent intended to be cranked and the master volume is used to determine overall loudness. Your more likely to need to crank a vintage style amp for high gain. If you want to look into different brands of power tube, again, on line reviews are a good place to look for information.

HTH

Chuck

[daz]

I find that it's hard to know when output tubes are losing tone because it happens so gradually. so what i do is always have another set on hand that i can use to compare. that way it's obvious. Pop in the known good set and compare.

[andyjazz]

I have an old tube tester that a friend of mine let me borrow. It's probably from the 60's or maybe 50's. Anyway I believe what it's telling me to a point. The thing is, when tubes have been running for a while the heat on the components can make them behave badly. I have a 64 Fender Pro Reverb that started developing classic power supply/rectifier symptoms ie; scratchy, dirty potentiometer-like sounds even when there is no input. Well, the easiest thing to check is the rectifier.

So I tested the rectifier on the old tester and it tested in the "good" range... I guess the rectifier COULD be ok but let me tell you, this sucker looks OLD. I'm changing out the old filter caps anyway (Oh yeah, they are the ORIGINAL caps!) and I'll probably replace the rectifier tube but.... thought I'd respond about the whole "life of a tube" question... Any thoughts about the veracity of tube testers?

[Enzo]

Tube testers can tell you a tube is bad, but they can't really tell you a tube is good. In my opinion.

Unless you have a very fancy tube tester, it will tell you that a tube functions, but won't tell you if it has lost its tone, won;t tell you if it is microphonic, won;t tell you if it is noisy.

Usually if a tester says a tube is shorted or has really low emission or some such, I tend to believe it. But really, in my repair business I never get the thing out anyway. If I think a tube is bad, I just slap another one in its place and find out a lot faster than setting up a tester.