HELP: TRRI breaking up on 3!!!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Fernando, Dec 30, 2005.

  1. Fernando

    Fernando Member

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    Hi folks. I'm sorry if this is a stupid question, but here we go:

    I have a Twin Reverb Reissue, into which I play only humbucker guitars. Today it got a little funny on me, and started breaking up in a very low volume (3).

    I don't know what could be wrong. It didn't do that before. With the volume on 3, it sounds as if I was using a low gain overdrive pedal in front of it. Even if I lower the volume knob on the guitar, it still distorts a little.

    What could be wrong? Could be a bad tube? I haven't changed a thing since I bought it in April.

    Please, HELP, I love the headroom on this thing, that's why I bought it.

    Thanks
     
  2. dave s

    dave s Member

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    Check and make sure all 4 power tubes are firmly seated in the sockets. That happened to me more than a couple times on my older twin.

    dave
     
  3. mr coffee

    mr coffee Gold Supporting Member

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    like power tubes.. running it into another cab..after first making sure the speakers are plugged into the mains and not the extention jack..:eek: been there done that
     
  4. Fernando

    Fernando Member

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    I believe you nailed it. One of the power tubes was a bit loose. I can't turn this thing on at this time though. It's 11 pm, and the neighbors hate my twin. I don't blame them :rolleyes:

    Thanks, guys, I'll let you know how it turns out tomorrow.
     
  5. Fernando

    Fernando Member

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    Well, I really don't know whats going on. One of the power tubes was a bit loose. I made sure that it is now firmly seated in it's socket. BUT, there was no diference regarding the problem. I tested the amp with my 3 guitars and it happens with all of them. Starting on 3 on the volume knob, the amp starts to distort a bit. It's barely noticeable. I can't hear it when I play single notes, but if I play any two notes toghether, it distorts a little bit. It sounds exactly as if I had my TIM pedal in front of it with the gain close to 0 (between 8 and 9 o'clock, for instance).

    I also noticed that the background hum is a little louder now. Could it be the speakers? Unfortunately I don't have another cab to test it with. The speakers are plugged in to the internal speaker jack.

    HELP!!!
     
  6. Serious Poo

    Serious Poo Armchair Rocket Scientist Graffiti Existentialist Gold Supporting Member

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    It's kind of a stretch, but your #1 preamp tube may be going. They usually last a long time, but they occasionally go bad and start acting up. Just a thought.
     
  7. Fernando

    Fernando Member

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    Yeah, I've been reading stuff on the internet and several articles mention that a frequent cause for unwanted distortion on clean settings are bad preamp tubes, namely tube #1. The amp comes with GT 12AX7s. What would you guys suggest as a replacement? I'm not after nothing too fancy. I can easily find most of the most popular brands here in Brazil, but that's about it.

    One other thing, and I'm sorry if it's just stupid (I confess, I'm new to tube amps and I know nothing about electronics!): I figure there's no need to rebias the amp after changing preamp tubes, is that right?

    Thanks again
     
  8. Serious Poo

    Serious Poo Armchair Rocket Scientist Graffiti Existentialist Gold Supporting Member

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    To the best of my knowledge, you rarely (if ever) need to rebias anything if you're only swapping out preamp tubes.
     
  9. Fernando

    Fernando Member

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    I'm thinking of buying new preamp tubes from Electro Harmonix. Do you guys have any experience with those?
     
  10. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Fernando,

    Tubes might be the cause but don't forget two important things; Humbuckers make amps break up sooner and check the height of your pickups in your guitars. I can take my tele and set my amp so it's barely breaking up but if I leave everything alone and then plug my Les Paul in the amp will be very distorted. If you want clean at higher volume levels do the following; make sure the phase inverter is a 12at7 (this tube is athe small preamp tube closest to the power tubes) and replace V2 (the second tube from the right) with either a 12ay7 or a 5751. Personally, I would just lower your pickups some and leave the amp alone.

    Electro Harmonix tubes are good but so are JJ's. The JJEcc83's will be darker then the EH's and when speaking of Fender's I think this would be a good thing.
     
  11. Fernando

    Fernando Member

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    I was also considering the JJ's, but I've read somewhere that they are more microphonic than the EHs. Is that correct?

    I'm aware of the higher output of humbucker pickups, and I've also tried to lower them, as well as playing with the volume on the guitar knob lower. It didn't help, unless in real extreme positions. The one thing that makes me think I have a bad tube os the fact that this unawanted breakup did not happen before. And nothing has changed: I play the same guitars, with the same pickup configuration, same settings on the amp, etc. But thanks anyway, I too would prefer to leave the amp alone, but I've tried all I could think of that wouldn't require changing parts. I just hope it's not the speakers.
     
  12. Guinness Lad

    Guinness Lad Silver Supporting Member

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    I don't know about JJ's being more microphonic, I guess anything is possible but I have had good success with them. The EH's are a brighter tube with more upper midrange.

    If you are using only the Vibrato channel on the amp switch V1 with V2. These are the two preamp tubes at the far right side of the amp when looking at the back of the amp. V1 will be the farthest to the right and V2 will directly to the left of it. V1 is the 1st gain stage on the normal channel and V2 is the first gain stage on the Vibrato channel. The rest of the amp is as follows: V3 reverb driver 12at7, V4 reverb return 12ax7, V5 vibrato 12ax7 and V6 is the phase inverter 12at7.

    Looking at the back of the amp you will see:

    6L6 6L6 6L6 6L6, phase inverter, vibrato, reverb return, reverb driver, Vibrato input, normal input
    power tubes V6 V5 V4 V3 V2 V1
     
  13. Roe

    Roe Member

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  14. megatonic

    megatonic Member

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    I'm using a Tung Sol for my Normal channel and an E-H for my Vibrato channel. Both sound great. I would have used Tung Sols in both channels but I thought I had more on hand than I did.
    I'll order some more and then install one in the Vibrato channel.

    The E-H 12AX7's sound very good, though.
     

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