New Amp...Tube Questions

Benny Hicks · 04-04-2003, 02:34 PM

Well guys, I finally got my amp. It's a Carvin Nomad 112, and I think it'll do nicely. I just received it today and haven't really had much time tinker with it, but I have a question about the tubes. I haven't replaced them or anything so the stock tubes are still in there, and I don't really know what to listen for to hear if they're damaged. If a tube is messed up is really obvious, or is it possible to have a damaged tube and not know it? Just for reference, my amp has 4 EL84's and 5 12AX7A's.

This is my first tube amp, and I've heard different things about replacing tubes. I've heard some guys say that you should should always replace all the tubes when you buy a new amp, and I've also heard different things about different types of tubes. Any of you guys have any words of advice? Anything would help. Thanks

Ben

gearup · 04-04-2003, 07:42 PM

There is no pressing need to replace the tubes in a new amp, unless they are damaged. You should be fine.

If they go bad you will know it. Sometimes the amp will squeal and hiss. There also might be a big drop in output. Finally, what I think is the most obvious sign is that the TONE will "flatten " out or loose its brilliance.

I can tell you that in your case, as with all EL-84 amps, that the EL-84 power tubes will last about 6mo to a year, and a little over a year for the 12ax7 preamp tubes. EL-84's are run a lot harder than thay were originally designed to, so they do not last as long as others, especially in a pure class A amp.

As for replacing them, ALWAYS replace the power amp tubes as a "matched" set, all 4 at the same time. The great thing about your amp is that EL-84's do not need any bias adjustment to the amp, and the amps character can be "tweeked" with different tube sets of varying plate voltage. I also feel it is best to replace all preamp tubes at the same time, not because it is critical, but if one is going then the others are not far behind, usually.

Probably a little more info than you were looking for. Just go enjoy the new amp. You got yourself a nice one.

Good Luck.

Benny Hicks · 04-05-2003, 07:27 AM

No way man, I'm looking for all the information I can get

Thanks for the tips though, I'm definitely enjoying it.

Ben

nate95366 · 04-06-2003, 02:52 PM

Definitely replace all power (EL84) tubes at the same time. You'll often be able to hear that one of them is going (flat tone, decreased output, etc.) before you can see it going (bright, fiery red instead of a nice soft orange glow). If you can see it going, shut the amp down and re-tube (wait a few minutes to avoid "frying" your fingers...) or risk blowing the output transformer (a very bad thing to do).

With the 12AX7 tubes, a class A amp will not drive them any harder than the next amp will, and my experience is that they last a lot longer than just a year, as long as you're not hauling your amp all over town, from hot weather to cold, banging against things and rattling and shaking a lot. Over time, certain ones of them will start to get microphonic, which means that vibration will change their output and you'll "hear" the external vibration in the speaker. Giving them a light flick with your fingernail while the amp is on is one way to test for this, but don't test every day. If it's microphonic, the amp will pop and "ting" with your flicking. People have been known to introduce microphonics into a tube by over-testing it this way.

I also don't find it necessary to re-tube the whole pre-amp section when one of them goes unless your amp has just fallen down the stairs or something. Often, when one 12AX7 goes, it's not because it's "burnt out" (like power tubes), but because something has vibrated loose and is microphonic. This is not a good predictor for what's happening in the other tubes (whereas if one power tube burns out, you can be pretty sure the other is headed there soon...).

Right now the 12AX7's in my Boogie have been going strong for 18 months and still have lots of life in them.

Nate

Benny Hicks · 04-07-2003, 01:47 PM

Alright, thanks for the tips, I appreciate all the advice I can get

Ben

FloridaYouthGuy · 04-18-2003, 12:08 PM

I agree with the above posters about replacing ALL the tubes at once... if you only replace the bad one then the new one will be burned out much faster... due to uneven loading...

Leave the tubes that are in it for now... they should be fine if the amp is new.

Oh and always let the amp warm up a good 5 to 10 minutes before crossing the tubes... hope this helps.

nate95366 · 04-21-2003, 08:05 AM

Quote:

I agree with the above posters about replacing ALL the tubes at once... if you only replace the bad one then the new one will be burned out much faster... due to uneven loading...

Again, this only makes sense in light of the power tubes. Pre-Amp tubes do not effect how the others are "loaded" in any way.

Nate

gearup · 04-21-2003, 10:47 PM

Nate is correct with regards to the preamp tubes. I just do them all at once because i am already there and they are cheap. It is HIGHLY suggested that you replace the preamp tube in the phase inverter socket with the power tubes. This is a very heavily worked tube and is not going to last through two sets, most of the time. A fresh, "balanced", phase inverter will make the power tubes work much more effeciently.

5L. · 04-22-2003, 05:50 AM

What are some of the popular brands that people like to buy?

Is there much difference between them?

gearup · 04-22-2003, 06:57 AM

There are really only about 4 or 5 tube makers in business today. There are others if you count NOS (new old stock), but these are often very expensive.

Of the new production tubes for your amp, you have Svletana, JJ's, Sovtek, Electro Harmonics (EH), and Chinese tubes. None are made in the USA. Everything else is made by one of these.

I perfer the JJ EL-84 power tubes. I think they are the best new tube on the market. Sovtek would be my next choice.

Preamp tubes are a matter of taste. The JJ's and the EH tubes are the best made, IMHO. both are very quiet and well made.

FloridaYouthGuy · 04-22-2003, 07:40 AM

Sovtek EL-34's are nice too... I just got some put in my amp a few months ago.... good price too.

Oops... just realized you don't use 34's... oh well...

nate95366 · 04-22-2003, 08:43 AM

I use straight-up Sovtek EL84's (with nice Russian print on the box and a hammer & sickle to add a nice repressive touch) on the power side and I use a mixture of Groove Tubes, Ruby Tubes, and basically whatever I can find that's cheap and not noisy on the preamp side. The not-noisy factor is REALLY important on the V1 and V2 tubes. On the others, it's frosting but still nice to have.

Nate

5L. · 04-23-2003, 12:42 AM

Cool, thanks for the suggestions. I think i'll try Sovteks first, since they seem to be the cheapest.

Seems like the tubes on ebay are pretty cheap

check out this site: http://www.eaudioguy.com/

5L. · 05-12-2003, 05:05 AM

Hello
I got some trouble shooting guys!

These couple of days.. it seems like when i tap my hand on the top of the amp , i can hear the tubes popping or something? Is this a sign that one of the pre amp tube have gone microphonic or something?

Also, when you turn your amp off or onto standby, do you guys kinda hear the tubes frying? lol

nate95366 · 05-12-2003, 06:21 AM

You shouldn't hear anything (other than maybe one "pop" on occasion) when you turn over to standby. As a rule, you shouldn't leave the amp on standby for more than an hour or so, though.

When you tap the top, you hear a popping noise? Do you have the reverb on? If so, that's it (and that means it's doing its job). If not, are you lightly tapping it or giving it a decent thud? One of your preamp tubes might be microphonic. The way lots of folks test for this is to let the amp warm up for a while, then without anything in the "input" of the amp and the gain and master set to "normal" playing volume, take a chopstick from an oriental restaurant or something lightweight like that and gently "tink, tink" on the outside of each preamp tube, in order, and listen. Since your amp is open backed, you don't need to strain to get in front of it to listen - you can listen right back where you're looking at the tubes from just fine... A little bit of "tink tink" noise coming through the speaker when you do this is "ok," but if it comes through with any real volume at all there's a good chance you've found the microphonic tube.

Nate

Nate