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Thread: amp question

  1. #1
    Eruption
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    12.31.69 @ 04:00 PM
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    I need a bit of help here. I own a Carvin MTS3212 100W tube combo. The clean sound was getting microphonic and the reverb wasn't working (its tube reverb). So I bought 5 new Sovtek 12AX7s and put 'em in. The reverb is back and the clean sound isn't microphonic anymore BUT now the volume seems to be a lot lower in general than it was with the old tubes. In fact I had it on 10 yesterday and although it was FUCKING LOUD, it was still nowhere near the volume of a 100W tube amp on 10 (I could stand in front of it and strum hard without felling like my head is gonna explode - and in the store the other day the guitar man had a bluesbreaker combo on 4 and it almost killed me!). It also seems to take a lot longer to warm up than it used to.

    This is the first time I've changed the tubes and its my first tube amp so I don't know what is normal. But I'd assume that (although there may be some subtle volume differences between tube brands) in general the preamp tubes shouldn't effect the volume all that much. There also seems to be way more bass now than before.

    Is this normal?

    If not, do you have any advice?

    [img]smilies/confused.gif[/img]
    RD<br /><br />"Rock 'n' Roll is my second favourite thing in the whole world" - DLR (1983)<br /><br />"We don't go for perfection, we just go for spirit." - EVH (1981)

  2. #2
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    12.31.69 @ 04:00 PM
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    Dudes, I just had an interesting advancement with the amp saga. I forgot to mention before that the tone is not only more bassey but it sounds like the volume on the guitar is rolled back to about 2. That's why there's no top end I think.

    Anyway, to my relevation...

    I had a note still ringing on the guitar and I flicked the standby switch off (at this point my volume is on about 5 but is still low in level) and I just got hit with this huge pulse of power (like what the amp should be sounding like on 5 with the presence and trebble on 10! [img]smilies/wink.gif[/img]). As soon as I flicked the switch off it raised in volume to where you'd expect it to be (on 5) and then died down like usual when the standby switch is turned off. I thought that was interesting. So obviously it wants to be loud but something is holding it back other than the split second after the standby switch is turned off (or is that on??? - What I mean is when you want to stop playing and you flick the standby switch... do you call that on or off?)

    Anyway, I thought that might spark a few ideas in your heads...

    Oh yeah, it only happens in the distortion channel - the clean channel is as usual.

    [ March 26, 2001 at 08:00 PM: Message edited by: Romeo Delight ]
    RD<br /><br />"Rock 'n' Roll is my second favourite thing in the whole world" - DLR (1983)<br /><br />"We don't go for perfection, we just go for spirit." - EVH (1981)

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    03.30.13 @ 09:28 AM
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    That amp uses 5881's, and EL-34's and has a bias switch. Is the bias set correctly?
    Your output tubes will tend to control the output volume, so I'd check that end of it first. It takes a long time to wear down your preamp tubes. Your output tubes will usually wear out much faster, especially at loud volumes, so if your preamp tubes are fried you can pretty well bet that the output tubes are done for as well. Take it in, and have the output bias checked, then outfit it with new power tubes. Even though the clean channel is working normally the high gain section requires more power to work efficiantly.

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    12.31.69 @ 04:00 PM
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    Thanks for the reply tribb. I checked the bias and it is set on 5881 - so that's no problem.

    I'll take my story a bit further and see if you can tell anything more.

    I went away on the weekend to visit a friend and another friend who had come out here from the States with some gear for me (including the tubes). Anyway, we put the new 12AX7s in and the amp sounded great - much better tha before. Then I took the amp to a friend's place where I left it for a few days while I came back to Sydney. Anyway, when I went back to pick it up the sound was really jerky - you know, I'd hit a chord and it would fade in and out etc. Anyway, I swapped around the first 3 preamp tubes (ie not actually replaced them but just put 1 where 3 was, 3 where 2 was and 2 where 1 was etc) and also did the same with the poweramp tubes. Then the amp seemed to work but the sustain was not as good as it used to be.

    A friend told me that when the poweramp tubes are no good, you know it because your amp stops working, but if the tone is getting worse then its the preamp tubes. Do you think it might be the poweramp driver 12AX7? I never swapped that one.
    RD<br /><br />"Rock 'n' Roll is my second favourite thing in the whole world" - DLR (1983)<br /><br />"We don't go for perfection, we just go for spirit." - EVH (1981)

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    12.31.69 @ 04:00 PM
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    Your phase inverter tube (that's the last preamp tube) is certainly a likely possibility. Put a new one in and see if that works. Is there an impedance switch on your amp? I didn't notice if you said it was a head or combo, but check to make sure the impedance is set properly for your speakers. That could cause a loss of tone and power.
    Don't bark at me...<b>I</b> didn't name ya.

  6. #6
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    12.31.69 @ 04:00 PM
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    Thanks for the help guys.

    I actually have 5 brand new 12AX7s in there right at the moment! They are Sovtek which I thought would be ok but maybe they are just a heap of shit - even with all the microphonics the old tubes had the tone was way better. I'll try swapping them around again. I don't think my reverb is as prominent as I remember either - maybe these tubes just don't have any guts!!?? [img]smilies/confused.gif[/img]
    RD<br /><br />"Rock 'n' Roll is my second favourite thing in the whole world" - DLR (1983)<br /><br />"We don't go for perfection, we just go for spirit." - EVH (1981)

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    03.30.13 @ 09:28 AM
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    There's different kinds of Sovtek tubes out there. Some have more gain than others, depending on the last letter after the 12Ax7.
    As a rule sovteks tend to be more distorted than some others, but they'll have no effect on your power output. Switching your preamp tubes shouldn't have been necessary if it was working fine to begin with, and switching the power tubes around is a waste of time. They should be replaced, and the amp should be rebiased after replacement.
    There are a lot of things that can go wrong in the circuitry of a tube amp and the tubes are only the last place you want to look.
    If a tube really malfunctions it can burn out part of the grid, and then you've got problems that changing tubes won't fix.
    It could even be something as simple as a bad ground in the high gain section. That happened to me once, and gave me the kind of problems you spoke of. I'd replace the power tubes first, and if that's no help then it's time for a visit to the amp doctor.

    [ March 27, 2001 at 08:43 AM: Message edited by: tribb ]

 

 

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