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  1. #1
    Little Dreamer
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    12.31.69 @ 04:00 PM
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    ANY TIPS ON CHANGING THE TUBES IN MY 5150 HEAD
    .. IVE NOT DONE THIS BEFORE SO ANY TIPS OR HELP WOULD BE APPRECIATED !! THANKS...
    <BR>BRENDO

  2. #2
    Sinner's Swing! Rick S's Avatar
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    06.23.17 @ 09:49 PM
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    i think the 5150 is a fixed bias amp. alot of modern tube amps are, especially peavey so they can be just plugged in........ personally i dont trust many amp techs to just rebias amps they always seem to find some other problem to charge you more than 20 bucks.
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  3. #3
    Good Enough
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    03.30.13 @ 09:28 AM
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    If you're just changing tubes there's no need to drain the capacitors. As a matter of fact that's an extremely dangerous thing to do if you don't know what you're doing. Thers' enough voltage in a power capacitor to kill you and then some.
    The will not discharge into the tube sockets so don't even worry about the capacitiors. Just avoid touching them. There's no reason to make contact with them while changing tubes.
    If you're just replacing the preamp tubes (small 12ax7's) then don't worry about it. You can simply replace them as the preamp section is self biasing and will "adapt" to the new 12ax7 tubes, regardless of the manufacturer.
    If you're replacing the large 6L6 power tubes then it might need biasing, depending on the tubes you use. If you use a replacement set of peavey 6L6 tubes then it's a straight exchange and done.
    If you're using groove tubes or a different manufacturer then it might need biasing.
    5150 amps are biased to take a medium tube (a rating of 4-6 if it's a groove tube)
    If the new tubes fall into that category you should be fine.
    If you're going with another manufacturer and you're not sure of the rating then a bias might be a good idea.
    Again, you can check with the manufacturer and see how their tube is rated for hardness. A power tube considered soft will break up earlier, while a hard tube will have to be pushed with more volume before it distorts.
    Although it costs more, it's alway a good idea to replace all the power tubes at the same time with a matched quad of 6L6s. If you're just replacing one or 2 tubes power tubes then biasing is a good idea because you want an even signal through the tubes and just by looking you can't tell which tube is the worst of the batch.
    With preamp tubes you can replace one or two at a time. It makes no difference.
    Since almost all the 5150 distortion is in the preamp section with the 12ax7's, until the amp's volume is way up, a medium rated power tube is fine, which is what your 5150 originally came with.
    To remove both the preamp and power tubes, first unplug the amp and make sure the tubes are cool.
    Grip the tube near the base and use a gentle circular rocking motion as you lift the tube out of the socket so you don't damage the tube socket or pins.
    Tubes fit snugly in the sockets so there's no electrical arcing from the tube pin within the socket so you want to keep that snug fit, and rolling it out in a circular motion is the best way to do that.
    When you remove a power tube look at the bottom of the tube. You'll notice a center post with a tab on it that lines up with a notch at the base on the 5150's tube socket. Just line up the new tube so the tab matches the notch and it'll fit in easily.
    12ax7's don't have that base, but you'll notice that there's a wider gap between 2 of the pins, which corresponds to a wider gap in the tube socket. Again just line them up before you insert the tube and then rock it into place.
    It's very easy.
    When reinstalling the tubes use the same motion, or a side to side motion to reinsert the tubes, this time pushing down.
    Take your time and it should be easy.
    If you do take it in for biasing, again keep in mind that it's only the power amp section they need to bias so if the amp is fine in all other respects there's no need for them to do any other repairs or modifications.
    Act informed and state that you simply want a bias for the power tubes and that's it.
    Although biasing isn't expensive I've seen shops that find the biasing to be perfect but will still charge you for a bias because they had to open the amp.
    I do my own biasing, which saves me time and money, but again if you use a mid rated power tube or original peavey power tubes you shouldn't need biasing of any kind.
    I've probably given you way more information than you need but you say you've never done it, and it's always good to be informed. You'll find changing tubes is a peice of cake.
    I'd rather change tubes than guitar strings.

    [ September 25, 2002, 10:43 AM: Message edited by: tribb ]

  4. #4
    Atomic Punk Wolfman's Avatar
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    07.20.17 @ 03:43 PM
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    Depends on if you are changing your preamp tubes or the power tubes. If you're doing the preamps, it's not that big of deal.

    If it's the power tubes, that's a whole different ballgame, because your amp needs to be rebiased after that, and if you're a newbie to those types of maintenance, you're better of having a shop do it for you for 20 bucks or whatever they charge these days. more importantly, you've got to be sure to drain the capacitors of any charge (it doesn't all disappear just because the switch is in the off position and unplugged) so that you don't deep-fry your heart with a nice arc from the amp. I've had a few guys that lived through that tell me about it, and they did not describe it as "fun".

  5. #5
    Little Dreamer
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    12.31.69 @ 04:00 PM
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    Thanks for the help guys... the more info the better for me so thanks Tribb... the replacement tubes Iv'e been quoted on are a matched quad of Svetlana 6l6GC's and Electro Harmonix 12AX7's .Any opinions on these tubes or other replacements would be helpful!! Does it sound like the Svetlanas as a matched quad will go straight into the 5150 without biasing??
    Thanks again
    <BR>BRENDO

  6. #6
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    03.30.13 @ 09:28 AM
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    Svetlanas are good tubes, and are usually a medium rated tube. Either way, Once they're in listen to how they sound, and check to see if the glow pattern is the same(do they glow aout as brightly as your old power tubes) when the tube is on and the amp has been running for about 10 minutes.
    There's not enough difference in the tube rating to present a problem to the head so don't worry about damage to your amp. It'll all be in the sound. I've replaced stock marshall and medium rated groove tubes with Svetlanas with no problem. Replace the power tubes first and have a listen after playing for about 10-15 minutes. If it sounds good then you should be fine. If the tubes seem to be glowing too brightly, which I really don't think will be a problem, you can have them biased down to reduce the voltage.
    I'm not a big fan of Electro harmonics tubes, but they'll work as well as any others.
    Preamp tubes will affect your overall sound quite a bit.
    If you don't play loudly they are your primary sound, and you'll find that russian tubes sound different from chinese tubes, which sound different from chzek tubes which sound different from american tubes, etc..
    If your amp has been getting quieter when you turn it up, or the sound seems to be fading in and out then it's just your power tubes and you may be fine after replacing them. If you hear a ringing or hissing that's not related to gain(it'll hiss even when the volume is low with the gain turned down), or popping sound when you play then you've got a bad preamp tube, which might only need a one tube replacement. It's easy to check.

  7. #7
    Romeo Delight
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    09.11.13 @ 09:10 PM
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    I HAVE BEEN USING THE SAME 5150 HEAD SINCE THE DAY THEY WERE INTRODUCED TO THE PUBLIC FOR SALE AND IT HAS ONLY BEEN REBIASED ONE TIME. THAT WAS WHEN I DROVE IT DOWN TO PEAVEY AND HAD TO HAVE A TRANSISTOR REPLACED SO I HAD THEM GO AHEAD AND CHECK IT OUT. I HAVE HAD EVERY TUBE KNOWN TO MAN IN THIS AMP AT ONE TIME OR ANOTHER AND I'VE FOUND THAT THE RUBY TUBES THAT PEAVEY FIRST USED IN THEESE AMPS IN THE BEGINING ARE THE BEST FOR THE ORIGINAL 5150 SOUND. SO I ONLY USE RUBY TUBES FOR THE PRE AND POWER SECTION OF MY ORIGINAL 5150. THE OTHER TWO ARE ALLS FAIR IN LOVE AND WAR I'LL TRY ANYTHING IN THOSE AT LEAST TILL I GET TIRED OF IT.
    Give me a bottle of anything and a jelly donut.....TO GO!!!!<br /> DLR 86'

  8. #8
    Top Of The World
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    12.31.69 @ 04:00 PM
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    I've been told by more than one repair shop, and one even showed the schematics...........the 5150 has a fixed bias.

  9. #9
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    03.30.13 @ 09:28 AM
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    I've been told by more than one repair shop, and one even showed the schematics...........the 5150 has a fixed bias.
    You're right. The 5150 does have a fixed bias, but it can be altered by a tech, to accomidate a different rated set of tubes than it was made for. A fixed bias means there's a fixed voltage that the amp delivers to the tubes, and the wrong tubes could burn up quickly.
    You can even add a cathode biased circuit, using a DPDT switch, and switch between the two, but it takes some modification to the circuit and you need to know what you're doing.
    I'm just getting into cathode biasing some small power circuits based on drawings other techs have given me.
    Some old silver face fender amps use a fixed/cathode biased switching circuit.
    There's actually quite a bit you can do to the inside of a 5150 to change the sound.
    That's why I mentioned that if you stick with a medium rated set of tubes there should be no problem. It's always a good idea to rebias any amp when a new set of (different manufacturer)power tubes are installed, and actually recommended especially on a fixed bias amp, but nothing will blow up if it's not, again, as long as the tubes are medium rated.
    If it's run too hot the tubes will wear out quickly(early VH), or a harsh sounding distortion if the bias is too low.
    If you're really in doubt and don't want to have it biased, then stick with the original type tubes from Peavey.

    I think I should probably add:
    Don't, "under any circumstances" go into the back of an amp and mess around yourself, unless you're qualified to do so!!

    [ September 30, 2002, 07:04 AM: Message edited by: tribb ]

 

 

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