how i know the tubes need replaced ?

[telbert twang]

hi,


What would be the signs of amp tubes needing replacement?


in fact, i suspect my laney vc 15´s (bought used 4 months ago, and it should be now 2 yrs old) tone seems to have some loss of brightness (comparing to 2-3 months ago), but i am not sure to trust my ears


rgds,

tt

[Guitarslinger1]

Your ears telling you that the amp doesn't sound quite as good as it used to is a good sign that it's probably time to change the power tubes.

There are no hard and fast rules. Among other factors, it depends on how much and how hard the amp is played. But if that VC15 is 2+ years old, and still has the original tubes in it, it's pretty safe to say that it is due for some new power tubes.

Some will argue that the preamp tubes should changed as well. Others will argue that they only need to be changed if they are problematic. Still others will just argue.

It's likely that you will hear a big improvement with a new pair of power tubes in that amp at this point. Where you got from there is up to you.

[telbert twang]

thanks for answering

So it might be the ´worn-out´tubes ...

Aren´t there any visually noticeable signs on a bad tube?


Are the original tube types ok or should i start looking for another brand ( it has: Preamp Valves 3x 12AX7 TAD ; Output Valves 2x EL84 TAD) ?

tt

[Guitarslinger1]

A worn out tube is not necessarily a "bad" tube, it's just tired.

No visible signs on power tubes that are worn out, just tired tone. Trust your ears.

And there are not necessarily any visable signs on a "bad" tube for that matter.

As far as brand choice, that's subjective, and up to you. The TAD 12AX7s and EL34s are very popular. I'd suggest that if you were happy with the TAD EL34s, just replace them with new ones, and see what you think after that.

[jh45gun]

I find that hard to believe 2.5 years will wear out a tube unless the amp is set up to wear them hard. My Silvertone `1472 has the origional tubes except for one power tube and it is over 40 years old and yes I had my tech friend check the tubes a good thorough check. I had my Super Reverb for over 20 years and I changed the tubes once and that was because the power tubes were getting gassy and I did not know that the blue did not neccessarily hurt things. For the record there was no noticeable change in performance. I think those that have an interest in selling tubes spread some info that amps need tube changes more often then they really should. Unless the amp shows signs of weaker sound or other issues I think if the amp sounds healthy then the tubes are ok.

[Guitarslinger1]

Originally Posted by jh45gun

I find that hard to believe 2.5 years will wear out a tube unless the amp is set up to wear them hard. My Silvertone `1472 has the origional tubes except for one power tube and it is over 40 years old and yes I had my tech friend check the tubes a good thorough check. I had my Super Reverb for over 20 years and I changed the tubes once and that was because the power tubes were getting gassy and I did not know that the blue did not neccessarily hurt things. For the record there was no noticeable change in performance. I think those that have an interest in selling tubes spread some info that amps need tube changes more often then they really should. Unless the amp shows signs of weaker sound or other issues I think if the amp sounds healthy then the tubes are ok.

One in every five Americans finds it hard to believe that the Earth orbits the Sun, yet it does...

Were the power tubes in these amps you are speaking of, old manufacture tubes, or made in China?

In the case of Telbert's amp, it was showing signs of weaker sound, which is why he started the thread in the first place. If you have other ideas for the cause of the loss of tone in the Laney VC-15 mentioned in his post, please share them with us.

The fact is that power tubes do degrade with use. As I stated in my previous post, among many factors, this degradation is greatly influenced by how often and how hard the amp is played. The age of the tube is not typically a factor. Another factor is whether or not an amp has a standby switch or an indirectly heated cathode rectifier such as a GZ34, 5V4 or certain 5Y3s. The lack of these allows the high voltage to be applied to the tubes when the power switch is thrown, before the tubes are warmed up, which causes cathode stripping. Cathode stripping causes tubes to degrade even more rapidly. This is one of the reasons that Blues Jrs and other amps that have no standby switch and have solid state rectification, tend to chew up power tubes relatively quickly. The subject of cathode stripping is one that's highly debatable. In general, it is not considered to be good for tubes to have the high voltage applied before the tubes have warmed up.

Another fact, that I hinted at above, is that new manufacture tubes simply do not last as long as old manufacture American, British and other Western European tubes. It's just the way it is. Those new manufacture TAD EL34s simply will not last as long as made in Britain Mullard EL84s, even under the best of conditions.

As with most anything, YMMV.

[jh45gun]

Originally Posted by specialty guitars

One in every five Americans finds it hard to believe that the Earth orbits the Sun, yet it does...

Were the power tubes in these amps you are speaking of, old manufacture tubes, or made in China?

In the case of Telbert's amp, it was showing signs of weaker sound, which is why he started the thread in the first place. If you have other ideas for the cause of the loss of tone in the Laney VC-15 mentioned in his post, please share them with us.

The fact is that power tubes do degrade with use. As I stated in my previous post, among many factors, this degradation is greatly influenced by how often and how hard the amp is played. The age of the tube is not typically a factor. Another factor is whether or not an amp has a standby switch or an indirectly heated cathode rectifier such as a GZ34, 5V4 or certain 5Y3s. The lack of these allows the high voltage to be applied to the tubes when the power switch is thrown, before the tubes are warmed up, which causes cathode stripping. Cathode stripping causes tubes to degrade even more rapidly. This is one of the reasons that Blues Jrs and other amps that have no standby switch and have solid state rectification, tend to chew up power tubes relatively quickly. The subject of cathode stripping is one that's highly debatable. In general, it is not considered to be good for tubes to have the high voltage applied before the tubes have warmed up.

Another fact, that I hinted at above, is that new manufacture tubes simply do not last as long as old manufacture American, British and other Western European tubes. It's just the way it is. Those new manufacture TAD EL34s simply will not last as long as made in Britain Mullard EL84s, even under the best of conditions.

As with most anything, YMMV.

Thanks for the info I guess I was equating things to the older well made tubes as my amps had them. So if SS recification is harder on tubes I did not know that as all my amps have had tube recification when they were tube amps and no standby switch it must be the cheaper tubes as when I had my Super Reverb half the time I never used the standby switch when turning on and like I said my tubes lasted for a long time and my Silvertone does not have a standby switch and them tubes have lasted for for over 40 years (61 vintage amp) so I guess it is the cheaper tubes maybe in the new amps. I was not being critical of you or your knowledge I just found it hard to believe tubes would only last that long when I have had them last for so much longer but they were not new chinese made tubes either. Thanks for the info.

[Guitarslinger1]

Originally Posted by jh45gun

Thanks for the info I guess I was equating things to the older well made tubes as my amps had them. So if SS recification is harder on tubes I did not know that as all my amps have had tube recification when they were tube amps and no standby switch it must be the cheaper tubes as when I had my Super Reverb half the time I never used the standby switch when turning on and like I said my tubes lasted for a long time and my Silvertone does not have a standby switch and them tubes have lasted for for over 40 years (61 vintage amp) so I guess it is the cheaper tubes maybe in the new amps. I was not being critical of you or your knowledge I just found it hard to believe tubes would only last that long when I have had them last for so much longer but they were not new chinese made tubes either. Thanks for the info.

No problem. I also remembered your post in the thread about tube biasing as well, and figured you were just looking to be contrary. My apologies.

If you don't trust info on the net in regards to vacuum tubes, there are many books on vacuum tubes, some going back to the 1920s that you may want to look into.

Best to always use the standby switch on your amps that have one, and give the tubes 30 seconds or more to warm up. Whether you have old manufacture or new manufacture tubes, you might as well do all you can to prolong their life.

If your SR has a GZ34 rather than a 5U4, it is slowing the application of the high voltage on its own.

[jh45gun]

I do not have it anymore I sure wish I did. No I am not trying to be contrary just trying to learn and understand and maybe my post sometimes come on too strong which I do not mean them to be or present my self as a know it all because I am not. These forums have taught me a lot and some times if they do not make sense to me I ask but maybe not in the right way as the printed word is harder to see what the speaker means then if you see them in person where body language clears up the message a lot. Sorry if ya got the wrong impression that was not my intent.

[Guitarslinger1]

Originally Posted by jh45gun

I do not have it anymore I sure wish I did. No I am not trying to be contrary just trying to learn and understand and maybe my post sometimes come on too strong which I do not mean them to be or present my self as a know it all because I am not. These forums have taught me a lot and some times if they do not make sense to me I ask but maybe not in the right way as the printed word is harder to see what the speaker means then if you see them in person where body language clears up the message a lot. Sorry if ya got the wrong impression that was not my intent.

Not to worry.

It seems like many times when one is trying to answer a question and help someone out, that there are those who feel that it is their duty to come out of the woodwork and start delivering kidney punches. I mistook you for one of them. My apologies.

[telbert twang]

sry, i´m not much ´at home´ with tubes :

EL34 is equivalent to EL84 ?

I remember reading something that 12AX7 has also some other numeric name ... ?

Is it some kind of US and Europe standards thing?

tt

[Smirkster]

TT:

EL34 is most definitely NOT equivalent to EL84.

The 12AX7 was sometimes also called 7025 or ECC83.

I hope new tubes and a bias check fix your tone problem. I sometimes wonder if my power tubes are going bad, as I've owned the amp at least four years now and have no idea how much older they are than that.

But the amp still sounds great after this time...granted, it's only been played at reasonable neighbor-friendly volumes.

[jh45gun]

Originally Posted by specialty guitars

Not to worry.

It seems like many times when one is trying to answer a question and help someone out, that there are those who feel that it is their duty to come out of the woodwork and start delivering kidney punches. I mistook you for one of them. My apologies.

Nope not trying no kidney punches as I know there are folks here with lot more knowledge than me I am just trying to learn or I should say re-learn. I took a electronics class back in the early 70's electronics always kinda interested me to a point but I and the instructor did not get along he was an ass and while I was working on a TV a tube rolled off the bench and hit the floor and he accused me of being too clumsey to be a tech and said he would not pass me for that reason as I was too clutzy to pass and I did not get a diploma from him even though my grades were passing. So I never went into the field. Years later it bugged me so much I put in a complaint at the school afer he was retired and they looked into it and gave me my diploma. By then quite a few years had gone by and I forgot too much of the stuff I had learned so I never pursued it. Building these amps have given me some satisfaction at least and a cheap way to get a couple of decent tube amps at least I hope my super build is as I am using trannies not associated with the kits. My 5e3 build our of a Zenith mono phono sounds great I am hopeing this Super made out of a Hammond Tone Cabinet will sound as good with the PT and chassis being used out of the Tone Cab and a Peavey OT and the board was bought pre loaded for me.

[sjhusting]

Originally Posted by telbert twang

sry, i´m not much ´at home´ with tubes :

EL34 is equivalent to EL84 ?

I remember reading something that 12AX7 has also some other numeric name ... ?

Is it some kind of US and Europe standards thing?

tt

yeah. Roughly speaking, the American system is:

nominal heater voltage (12 for 12.6V, 6 for 6.3V ans so on)
Random letters (AU,AX,L,V)
The number of components in the tube (7 in a 12AX7: 2xplate, 2xgrid, 2x cathode, 1xfilament)

this has nothing to do with alternate systems, like for a 5751, 6072, or so on.

The European system is:

1 letter for the heater type (E=6.3V, P=constant current series, U, others)
1 or more letter for what the tube is (C=triode, F=small signal pentode, L=power pentode, etc)
first digit is basing (8=noval, 3=octal, 9=7pin mini, 7=submini, etc)
then individual numbers
so ecc83 is a noval-based (8) dual triode (cc) with 6,3V filament (e)

there are variations, like e88cc, or ef808, but mostly it's pretty logical, you see immediately from the designation what the tube is. And you know that el84 and el34 are not subs, because among other things they take different sockets. (3 vs 8)



steven

[Guitarslinger1]

Originally Posted by telbert twang

EL34 is equivalent to EL84 ?

No no. That was a typo on my part. My fingers seem to think they are equivalent when I'm typing, but they certainly are not. My apologies for the confusion.