[riddley]

Quote:

Originally Posted by Hirsch ...If you don't have a Variac, then the next best thing is to simply turn on the amp, but not to run signal until the tubes have had an hour to warm up. You only need to do this once for tubes that haven't been used since they were stored, which could be 30 to 60 years on the shelf.

If you don't do this (I didn't with my new tubes), does it permanently affect the sound of the tubes thereafter, or does it just mean they take longer to break in?

 

[Hirsch]

Quote:

Originally Posted by riddley If you don't do this (I didn't with my new tubes), does it permanently affect the sound of the tubes thereafter, or does it just mean they take longer to break in?

There is some controversy about this, as effects are not clear. The general thinking is that this procedure will reduce the chances of the tube going noisy, and increase tube life. It's not completely clear that this is so. However, my own feeling is that it can't hurt to play it safe.

 

[gort]

There should be a tubes FAQ. So far I learned never to switch phones unless amp is off or in stand by mode (not sure about amps without that mode like mine) and warm up a new tube for an hour without any signals.

 

[riddley]

Yep, wish I'd learned both those things a few weeks ago... starting out with a tube amp is quite a learning curve.

I've got a cyber-20 amp with two EL84 power tubes, both of which give a ringing tone when tapped. Does that mean they are microphonic? When I'm using the amp, I can't hear any effects of microphonics that I'm aware of - at least there's no extraneous noise present. Is there anything else I should be listening for to hear if the tubes have problems?

 

[mikeg]

Quote:

Originally Posted by Hirsch No, but there's likely to be mechanical vibration from the transformer(s), footsteps, etc. Still, a microphonic tube may still be very usable. In stages with low gain, microphonics can be much reduced. It's not a good idea to tap on a tube to test for microphonics. Usually it won't matter, but every now and then you can damage a tube. It's hot, and if something dislodges...

I'm glad that I started this thread because it brought out some really useful basic information for novices like me. Here are some questions regarding possible tube damage. If tapping hot tubes can damage them, how about pulling out hot tubes during tests and comparisons of tubes by tube rolling? I normally turn off the amplifier, but I don't wait for the tubes to cool off. Is this OK? Heck, if I have to wait for tubes to cool off, such comparisons will take much longer, and It'll be harder to recall small differences. BTW, I know that large tubes (such as 300B tubes) should be gripped by their base (i.e., avoid fingers touching the glass), but is it OK to touch small tubes with bare fingers?

 

[Hirsch]

Quote:

Originally Posted by mikeg I normally turn off the amplifier, but I don't wait for the tubes to cool off. Is this OK? Heck, if I have to wait for tubes to cool off, such comparisons will take much longer, and It'll be harder to recall small differences. BTW, I know that large tubes (such as 300B tubes) should be gripped by their base (i.e., avoid fingers touching the glass), but is it OK to touch small tubes with bare fingers?

Many small tubes don't have plastic bases. You have to pull them by the glass. I use my bare hands, but I'd bet that some people use cotton gloves.

My amp will play for a minute or two if I unplug it. There is power stored in the reservoir caps in the power supply. Even if the amp is off, the tubes will be getting current for several minutes. You don't need to wait for the tubes to cool completely, but it is a good idea to wait a couple of minutes so that you're not pulling tubes from a completely live circuit.

 

[ServinginEcuador]

Quote:

Originally Posted by riddley I've got a cyber-20 amp with two EL84 power tubes, both of which give a ringing tone when tapped. Does that mean they are microphonic? When I'm using the amp, I can't hear any effects of microphonics that I'm aware of - at least there's no extraneous noise present. Is there anything else I should be listening for to hear if the tubes have problems?

I'm using a Cyber-30 right now and it does the same thing. I'm not convinced that it's not a problem with the chassis more than the tubes. The metal chassis seems to be the fault here, but I could be wrong.

 

[Hirsch]

Quote:

Originally Posted by ServinginEcuador I'm using a Cyber-30 right now and it does the same thing. I'm not convinced that it's not a problem with the chassis more than the tubes. The metal chassis seems to be the fault here, but I could be wrong.

Actually, the metal chassis can be a good tester for microphonics. It's safer to tap on the chassis than the tube. If you hear the ringing, you've got a microphonic tube. Look to stages with the highest gain first. A non-microphonic tube will not ring if you tap on the chassis.

 

[fredpb]

Quote:

Originally Posted by mikeg Is there a need to condition new tubes such as 300B tubes? If yes, then how should they be conditioned? How does their sound after they've been used for a while?

I used to do a lot of work with tubes in the military. Including preventive maintenace so I could really learn about tube aging.

The best thing to do with new tubes is to leave them on. They will break in and age, especially the first few months. Over time, they will lose gain.

Two main problems with tube failure were shorting out internal elements, and microphonics.

 

[mikeg]

Quote:

Originally Posted by fredpb I used to do a lot of work with tubes in the military. Including preventive maintenace so I could really learn about tube aging. The best thing to do with new tubes is to leave them on. They will break in and age, especially the first few months. Over time, they will lose gain. Two main problems with tube failure were shorting out internal elements, and microphonics.

Are you suggesting leaving tube amps on 24x7? Aside from the amount of heat produced, will that not shorten the useful life of the tubes?

 

[ServinginEcuador]

Quote:

Originally Posted by mikeg Are you suggesting leaving tube amps on 24x7? Aside from the amount of heat produced, will that not shorten the useful life of the tubes?

A debate to which no one will admit that there's a right answer. Some say if you use your amp less than X hours per day, leave it on all the time. If less, turn it off. I guess each amp is different. Some use a soft turn-on feature so that the full plate voltage isn't applied for 30 second to a couple of minutes. By doing that you shock the tubes less, thus extending their lives. The Melos amps have a 30 second delay built-in, which eliminates the need for leaving it on all the time.

I personally just turn the amp off and one each day when I use it. I don't worry about the tube lifespan too much, nor do I put much thought into it.