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Tube gurus! I beseech thee!

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  • Tube gurus! I beseech thee!

    I'm trying to at least marginally improve the headroom on my silverface Bassman. There are also some ugly microphonics I'd like to tame. Here are the tubes:
    Preamp: 7025 (2)
    Power: 6L6GC (2)
    Phase inverter: 12AT7

    Any recommended swaps? It also might be worth noting that these tubes are all pretty old with the exception of the 6L6's, which are maybe 10 years old and have seen fairly limited duty in that time.
    <div class="signaturecontainer"><a href="http://codpiece.bandcamp.com" target="_blank">My rock band</a></div>

  • #2
    I'm trying to at least marginally improve the headroom on my silverface Bassman. There are also some ugly microphonics I'd like to tame. Here are the tubes:
    Preamp: 7025 (2)
    Power: 6L6GC (2)
    Phase inverter: 12AT7

    Any recommended swaps? It also might be worth noting that these tubes are all pretty old with the exception of the 6L6's, which are maybe 10 years old and have seen fairly limited duty in that time.


    replace the first couple (or all) of preamp tubes with 12at7's. the microphonics problem is probably one of your current preamp tubes.
    <div class="signaturecontainer"><a href="http://www.guttermouthelectronics.com/" target="_blank">http://www.guttermouthelectronics.com/</a></div>

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    • #3
      I'm trying to at least marginally improve the headroom on my silverface Bassman. There are also some ugly microphonics I'd like to tame. Here are the tubes:
      Preamp: 7025 (2)
      Power: 6L6GC (2)
      Phase inverter: 12AT7

      Any recommended swaps? It also might be worth noting that these tubes are all pretty old with the exception of the 6L6's, which are maybe 10 years old and have seen fairly limited duty in that time.


      I would also suggest rebiasing the amp. If you are having nasty harmonics, you are getting crossover distortion.
      <div class="signaturecontainer">Igitur qui desiderat pacem, praeparet bellum.<br />
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      • #4
        I had a '59RI Bassman, and no mods could give that thing a useable amount of headroom for clean tones. Ironically, the AC30, whcih is 15 watts less, has a LOT more headroom.
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        • #5
          i'd give a crack on replacing yer 7025's and the at. one of them's the culprit, no doubt over the power tubes.

          you could try any number of tubes in the place of the 7025's-- usually they're up there for low gain headroom-- but i had good luck in those silverface circuits with 5751's, or a 5751 in the v1 position, and a 12 ax in the v2. the 12at actually DOES make a significant difference as the divider-- so if you can find a smooth NOS tube-- it can seriously change the character of the amp-- besides, its only one tube-- so even if it's $20 or so-- it's important too, so don't skimp..

          if that doesn't take care of your problems-- THEN move onto your power tubes...

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          • #6
            Thanks for everybody's input. I think I'm going to track down a NOS Mullard 12AT7 for the splitter and two Sovtek 5751's for the pre-amp.
            <div class="signaturecontainer"><a href="http://codpiece.bandcamp.com" target="_blank">My rock band</a></div>

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            • #7
              nice combo! bet that sounds bomber-- report back!

              Comment


              • #8
                I'm the king of scoring ancient tube amps that haven't had their tubes changed since birth. If no tubes are newer then ten years old I'd suggest changing everything down the line. Start of with the peramp tubes of course and if you have the money do the powertubes. If its your number one gig amp sell some blood or organs on the black market if thats what it takes to swap out the power tubes too. If your planning on recording with the amp start selling other peoples organs too! My main amp is a silverfaced twin so I kinda know where your coming from. I had microphonic power tubes when I got it and silly as I was at the time I thought my reverb was broken. I took it to a tech to swap out the powertubes (i had a few preamp tubes myself but not enough) and I told him to knock out the mastervolume from the circuit (the cheapy blackfacing). I kinda wish I didn't do that before hearing it with the fresh tubes.
                Here is a trick to help with old tubes before you get new ones. Unplug your amp and pull out a tube. Sand the pins and give the socket a little squirt of WD40. Ancient tubes can suffer a case of the crusties so that your connection isn't good. Its kind of an on the spot helper when you rescue something from the dead. I had an amp that I picked back from the trash brought back to life this way which was awesome cus it ran on almost all discontinued tubes. Don't go crazy with the WD40 and give it plenty of drying time before you plug in again. I've usually left it to be the last thing before going to bed at night and then just played the amp the next day. Also might want to try some fine fine sand paper in your inputs to make sure they are crust free and another small squirt of the WD40.
                Once you have that amp up and running with fresh tubes your gonna love it!

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                • #9
                  I don't mean to flame at all. But, please get some proper contact cleaner or DeOxit and leave the WD40 in the garage
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                  • #10
                    I don't mean to flame at all. But, please get some proper contact cleaner or DeOxit and leave the WD40 in the garage


                    never used or even seen the stuff. WD40 has done the trick and its readily available. Its what they use at the guitar shop here in town too. How different are the ingredients to DeOxit? If you think using WD40 for this is bad have a talk with the idiots who spray their fishing lures with the stuff cus some moron way back in the 80s convinced people that it worked wonders... I'm pretty sure that myth is what the episode of King Of The Hill was based on where Hank used crack rock to catch bass. Just imagine what it could do if you melt it down and soak it into your speakers. AWESOME TONE I TELL YOU WHAT!

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                    • #11
                      I

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                      • #12
                        Thanks for everybody's input. I think I'm going to track down a NOS Mullard 12AT7 for the splitter and two Sovtek 5751's for the pre-amp.


                        Go with the GE 5751 man, they are mil spec tubes that will out last you, and probably your kids, hell they might outlast the damn amp.
                        <div class="signaturecontainer"><div class="bbcode_container"><br><div class="bbcode_quote"><br><div class="quote_container"><br><div class="bbcode_quote_container"></div><br><div class="bbcode_postedby"><br><img alt="Quote" src="images/misc/quote_icon.png">Originally Posted by <strong>LoopQuantum</strong><br><a rel="nofollow" href="showthread.php?p=40147536#post40147536"><img alt="View Post" src="images/buttons/viewpost-right.png"></a><br></div><br><div class="message">It would never work. You're in outerspace, and breathing is a bitch.</div><br></div><br></div><br></div><div class="bbcode_container"><br><div class="bbcode_quote"><br><div class="quote_container"><br><div class="bbcode_quote_container"></div><br><div class="bbcode_postedby"><br><img alt="Quote" src="images/misc/quote_icon.png">Originally Posted by <strong>BrendanO</strong><br><a rel="nofollow" href="showthread.php?p=40124529#post40124529"><img alt="View Post" src="images/buttons/viewpost-right.png"></a><br></div><br><div class="message">There is something very wrong with a situation when I'd rather sleep with the naked cowboy.</div><br></div><br></div><br></div><font color="Purple"><font size="3"><b>Vice President o' </b></font><b>t<font size="3">e</font><font size="4">h </font><font size="5">b</font><font size="6">o</font><font size="7">os</font><font size="6">t</font><font size="5">e</font><font size="4">d </font><font size="3">m</font>idz club</b></font><br><font color="DarkRed">Great deals with; ENdtime, OverDriven, outforblood</font></div>

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                        • #13
                          Go with the GE 5751 man, they are mil spec tubes that will out last you, and probably your kids, hell they might outlast the damn amp.


                          I use a GE 5751 in V1 in my Blues Deville. Very happy with the sound, but have heard that Jan-Philips 5751 are even better. True?

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                          • #14
                            I'm trying to at least marginally improve the headroom on my silverface Bassman. There are also some ugly microphonics I'd like to tame. Here are the tubes:
                            Preamp: 7025 (2)
                            Power: 6L6GC (2)
                            Phase inverter: 12AT7

                            Any recommended swaps? It also might be worth noting that these tubes are all pretty old with the exception of the 6L6's, which are maybe 10 years old and have seen fairly limited duty in that time.


                            10 years is a long time for new production (not US made tubes) so replacing them with the correct types may make a big difference. The power tubes wear out the fastest so installing new power tubes can help a lot.

                            If the amp hasn't had a cap job done in the last 20 years or doesn't have the bias set correctly, doing these things can help a lot too.

                            If everything is up to date, replacing V3 (for the normal channel) with a 5751, 12AT7 or 12AY7 will clean it up.
                            <div class="signaturecontainer"><div class="bbcode_container">
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                            <div class="bbcode_postedby">
                            <img src="images/misc/quote_icon.png" alt="Quote" /> Originally Posted by <strong>TIMKEYS</strong>
                            <a href="showthread.php?p=46523189#post46523189" rel="nofollow"><img class="inlineimg" src="images/buttons/viewpost-right.png" alt="View Post" /></a>
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                            <div class="message">obama doesnt have that problem ,, hell he doesnt even know who his father really is. His momma was too busy takin off her clothes for some pervert commie who knocked her up and then got grad student to be the stand in baby daddy.</div>

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                            • #15
                              I use a GE 5751 in V1 in my Blues Deville. Very happy with the sound, but have heard that Jan-Philips 5751 are even better. True?


                              There's no consensus on what sounds better...it's all subjective.
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                              <div class="bbcode_postedby">
                              <img src="images/misc/quote_icon.png" alt="Quote" /> Originally Posted by <strong>TIMKEYS</strong>
                              <a href="showthread.php?p=46523189#post46523189" rel="nofollow"><img class="inlineimg" src="images/buttons/viewpost-right.png" alt="View Post" /></a>
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                              <div class="message">obama doesnt have that problem ,, hell he doesnt even know who his father really is. His momma was too busy takin off her clothes for some pervert commie who knocked her up and then got grad student to be the stand in baby daddy.</div>

                              </div>
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