burning tubes in??

Had new tubes put in (pre amp; power) and the amp sounds strange. Is there really a quot;burning-inquot; period? The amp now doesn't quot;singquot;, and the crunch doesn't fade off smoothly, but merely dies suddenly during the guitars sustain. Should I give em some time, or just have it looked at again.

Did you get it biased?

I took it to the quot;luxuryquot; guitar boutique (it sells mostly PRS/Gibson), and assured me that it would be done properly...so, i hope it was biased.

what amp is it? you should hear the improved difference instantly !!!!

Yeah!! when i got my amp revalved and biased back in january there was a big improvement in sound quality the moment it was turned on.

New tubes do need a burn in period, but the tube manufacturers or places like Groove Tubes who re-lable tubes handle the burn in, to make sure they are stable and can be biased properly. Once the tubes reach you they should be good to go.

If you had a professional change the tubes and set the bias, you have a right to be happy. Remember, he can't change the sound of the tubes you selected (if you selected the tubes). However, he can adjust the bias a little hotter or a little cooler in an attempt to get the tone you want.

Pre-amp tubes will also GREATLY effect the tone of your amp. What did you have in, and what did you chage to?

Give us a little more info. What kind of amp? What kind of power tubes?

It's a Hughes amp; Kettner Studio 84 (aka Tube 20) amp. Two 12ax7 on the preamp and EL 84 on the Power side. I bought the amp used and saw that there wer Hamp;K tubes in there. They were rattling and considering the amps 10 years old, i thought it best to change them. The sound now has weak bass, eq has little effect and the crunch dies off the ringing note in an ungraceful and sudden way, while the rest of it keeps going clean for a bit longer. Chords sound uninspiring and almost unmusical. In there now are all Electro-Harmonix tubes, from the little black boxes. He suggested them as they were robust (it's a combo y'see).

The Power amp section actually sounds not too bad. When i use clean channel, with very little gain, but lots on the power stage, it's nice. But use pre-amp gain, and it's that discordantish nastyness. ANd the touch-sensitive has gone too. No sweetness.

Like Jeff said tube burn in is done by the vendor B4 it get's to you. Do
you have the old tubes to put back in for a A/B comparision?


Originally Posted by kmcguitarsLike Jeff said tube burn in is done by the vendor B4 it get's to you. Do
you have the old tubes to put back in for a A/B comparision?

I thought of doing that, but was scared that if indeed it had been re-biased for the new tubes, it might cook the old ones, or break something else. The tricky process of biasing the amp is the reason i sent it in, otherwise i would have bought two sets of new tubes and quot;experimentedquot;

Anyway, i sent it in to another shop official Hamp;K dealer, so hopefully it gets more sweetness and sound this time.

that's odd because it's something the amp tech should have picked up on right away before you even let you go home with the amp.

take it back to the guy you paid. tell him it sounds like crap, wassup?

he might have biased it too cold. You can always swap preamp tubes as they do not need to be biased. So, take V1 and V2 and swap the tubes with each other. See if it gets any better. Might be a crappy tube.

Wait a minute....do you have to bias EL84's? I thought they were just plug and play? To me it sounds like a problem with the pre-amp tubes. I think one of the Groove Tube 12AX7-M's or 12AX7-C's would be a better choice than the EH's...even some JJ's.

I'd start with taking it back to your tech and having him look at it. For what you paid, you should be satisfied.


Originally Posted by Jeff_HWait a minute....do you have to bias EL84's? I thought they were just plug and play?

The tech, whom i spoke to on the phone, seemed to imply the same thing. When i told him the amp was EL84 in the power section, he dismissed my biasing question.

If that's true, I can then surely just go off and buy my own pre- and power tubes and drop them in. But the amps manual refers to Re-Biasing when changing power tubes??? Either way, i'm going to check the differences by rotating the new for old 12AX7. And rotating those amongst themselves. This poses no bias related problems, right?

The problem here in my country, is that there's nobody interested in offering a quot;tone-carequot; kind of amp service. Drop in the corrrect spec and move on. It's hit and miss. Don't even ask about what the tone character might be! If it works, it's a job well done. You get looked at funny if you say stuff like quot;it's overdrive/breakup is rather un-musical and harshquot; What? It works!

I'd move some different preamp tubes in there and see what happens. No biasing issues involved and any 12ax7 should show some sort of change.

Even though tubes are ready to go out of the box I did hear an improvement in tone with my JJs after I put 20 hours on them. The EL34s in my Marshall did the same thing and improved in tone over time. There may not be a burn in period but there seems to be a break in period, at least to my ears.

There is such a thing as a bad sounding tube even if it operates to spec. Thats why I suggest trying a different or even a couple of different preamp tubes. Just because it lights doesn't mean it's right.

Techs in the US are no different and you have to search around before you find one that is good and cares about YOUR tone. Keep looking.