2:90 silly questions...i could't answer

[danielL]

Hi friends!
I need some help please. I own a triaxis with 2:90 poweramp. Last night, i was playing with my band and my amp's volume raised incredibly. I checked the output meter in my multifx and it was normal, so i asume the problem is in the poweramp. I called mesa's support and they told me to check the power tubes, he said i can change them by myself. Then i called my local musicstore and asked them about retubing and they said i should take the amp so they would change the tubes and ADJUST THE BIAS. I think there is too much MISINFORMATION for a newb like me....so here are my silly questions:

1.- Has anyone experienced volume rise with this amp? I've only heard tube failure causes volume drops. Volume rise is new to me.

2.- I run my amp only trough channel A. Are the tubes in channel B wearing as much as in channel A? If not, should i just replace the tubes from channel A? Will i damage my amp if i use one channel while the tubes in the other channel are failing?

3.- If i buy 6L6s from mesa, do i need bias adjustment? can i change them by myself?

4.- Does the color in 6L6s matter so much? will i damage my amp if i use wrong colors?

5.- What are the 3 tubes inside the 2:90 for? should i change them too?

6.- How often do you change your tubes?

Thanks.

 

[danielL]

I just read this in mesa boogie's page:


All Mesa/Boogie power amps can be used in mono by connecting the input and speaker to one side only. The input of the side not in use cannot be connected or damage may follow. As with any tube amp, a load of some sort must be implemented if there is an input signal connected to the amp. Always make sure to connect the speaker to the appropriate side receiving the input signal. As an extra precaution, the volume of the side not in use should be turned all the way down and the Presence control turned all the way up. The 20/20, like all Boogie power amps is not bridgeable, but can safely be used in mono if the above-mentioned conditions are followed. We suggest alternating sides used in mono to provide even tube wear from Side A to Side B.

Tien Lawrence
Boogie Customer Support





TUBE TIPS....Tone is Colorful!

Mesa/Boogie has always built the versatility and tonal potential into the tone controls and features of the amp, leaving the finicky variation of different tube types aside.

Mesa/Boogie amplifiers employ a preset bias to allow even the least technically oriented player to change tubes themselves and maintain the original brilliant and dynamic response from the amp. The preset bias also means that Mesa will accept a much narrower range of tubes at much closer matching tolerances, considering the window provided by the preset bias. Other manufacturers and distributors accept tubes of much more extreme current draw and match variation under the guise of bias adjustability, claiming that tubes of different current-draw offer different response.

Tubes of similar type can vary slightly in response, but variations are more dependent on the bias adjustment.( For more in depth bias discussion, see Randall Smith's article on biasing in previous Amplitudes newsletters and on our webpage at www.mesaboogie.com). In the end, for any amplifier, Mesa tubes are more stringently tested, more closely matched, and from the most consistent and reliable of tube production ranges... the middle. Our tubes don't run hot or cold...They run RIGHT! We test and match the tubes for you, which is less time spent trying to tweak the amps circuitry, and more time playing and searching for tones with the amps tone controls and features.

Mesa/Boogie tubes have a three letter color code at the base of the tube used to group the tubes into matched pairs. These color codes do not apply to different tonal variation (the number and two letter codes with the color code are Production Batch #'s and Tester's initials respectively).

Any Mesa tested tube is guaranteed to perform tonefully and reliably within the preset bias of the amp, as long as matched pairs are in the appropriate sockets. No fuss, no muss! Just plug and play when it is time to re-tube. Maintain the TONE! Use Genuine MESA Tubes!

Tien Lawrence
Boogie Customer Support


I hope this is information will be helpful for tube newbies like me

 

[VijfZiel]

Hi friends!

1.- Has anyone experienced volume rise with this amp? I've only heard tube failure causes volume drops. Volume rise is new to me.

2.- I run my amp only trough channel A. Are the tubes in channel B wearing as much as in channel A? If not, should i just replace the tubes from channel A? Will i damage my amp if i use one channel while the tubes in the other channel are failing?

3.- If i buy 6L6s from mesa, do i need bias adjustment? can i change them by myself?

4.- Does the color in 6L6s matter so much? will i damage my amp if i use wrong colors?

5.- What are the 3 tubes inside the 2:90 for? should i change them too?

6.- How often do you change your tubes?

Thanks.

1.- In my experience with tube heads and preamp etc, I havent experience volume increases, so in this point I cant help !! sorry!

2.- Yes, the tubes in channel B use the same as the tubes of channel A. Like the document that you found said, alternate channels. Also in the manual of the 2:90 said that when you run the amp in mono, put the presence all the way up in the channel you are not using! I recommend that you connect your TriAxis in stereo to avoid all of this... hehehe

3.- You dont need bias adjustment if you change tubes for the same type. I mean, if you decide to change your 6L6 tubes to EL-34 tubes, it would need bias re-adjustement, if you change old 6L6 for new 6L6 you dont need to adjust nothing. Another important thing is that only specialst do bias adjustment, and if someone other than mesa do this, it would void your warranty. Keep an eye in the dual and triple rectifier, in the rear panel there is a switch where you decide the bias: 6L6 or EL-34. This amps do not need bias adjustment. And yes, you can replace them by yourself.

4.- I dont know what colors are you talking about hahaha but dont worry... There will be no problem if you replace tubes for the same type.

5.- There are 12AX7 I think. I havent read what are they for, but I dont think you need to change them.

6.- The replacement of tubes depends on almost everything. If you connect in mismatch the 2:90 and the cabs, it would wear down fastier the tubes. If you dont let the tubes to warm up, the same. In my personal experience, I have used my RK II once a week for almost 2 years and I havent had the need to change tubes. In the Triaxis and the 2:90 the same...

Hope it helps!!!

 

[VijfZiel]

Hi friends!

1.- Has anyone experienced volume rise with this amp? I've only heard tube failure causes volume drops. Volume rise is new to me.

2.- I run my amp only trough channel A. Are the tubes in channel B wearing as much as in channel A? If not, should i just replace the tubes from channel A? Will i damage my amp if i use one channel while the tubes in the other channel are failing?

3.- If i buy 6L6s from mesa, do i need bias adjustment? can i change them by myself?

4.- Does the color in 6L6s matter so much? will i damage my amp if i use wrong colors?

5.- What are the 3 tubes inside the 2:90 for? should i change them too?

6.- How often do you change your tubes?

Thanks.

1.- In my experience with tube heads and preamp etc, I havent experience volume increases, so in this point I cant help !! sorry!

2.- Yes, the tubes in channel B use the same as the tubes of channel A. Like the document that you found said, alternate channels. Also in the manual of the 2:90 said that when you run the amp in mono, put the presence all the way up in the channel you are not using! I recommend that you connect your TriAxis in stereo to avoid all of this... hehehe

3.- You dont need bias adjustment if you change tubes for the same type. I mean, if you decide to change your 6L6 tubes to EL-34 tubes, it would need bias re-adjustement, if you change old 6L6 for new 6L6 you dont need to adjust nothing. Another important thing is that only specialst do bias adjustment, and if someone other than mesa do this, it would void your warranty. Keep an eye in the dual and triple rectifier, in the rear panel there is a switch where you decide the bias: 6L6 or EL-34. This amps do not need bias adjustment. And yes, you can replace them by yourself.

4.- I dont know what colors are you talking about hahaha but dont worry... There will be no problem if you replace tubes for the same type.

5.- There are 12AX7 I think. I havent read what are they for, but I dont think you need to change them.

6.- The replacement of tubes depends on almost everything. If you connect in mismatch the 2:90 and the cabs, it would wear down fastier the tubes. If you dont let the tubes to warm up, the same. In my personal experience, I have used my RK II once a week for almost 2 years and I havent had the need to change tubes. In the Triaxis and the 2:90 the same...

Hope it helps!!!

 

[danielL]

Thanks VijfZiel!

 

[VijfZiel]

no prob friend!!!

 

[msi]

The three tubes inside the 2:90 have two reasons for being there. Each tube has two triodes, each triode is an individual gain stage. So the three 12ax7s have six gain stages total.

One tube is split between channel 1 and 2. They are the input buffers and increase the gain of your signal. One triode of the tube for each channel. The last two tubes are to split the signal in half and is called the phase splitter. The phase splitter of the amp requires two gain stages, or one tube each. So the two remaining tubes are each used as the phase splitter for channel 1, and channel 2. One tube for channel 1, and the last for channel 2.