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1099 Views 10 Replies Latest reply: Nov 8, 2011 4:57 AM by broadfca RSS
broadfca Just Startin'
broadfca
21 posts since
Dec 1, 2010
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Oct 29, 2011 2:54 AM

DT50 Preamp Tubes (one ot two stage preamp)?

My DT50 Amp has two (2) preamp tubes. Is this because it's a two (2) stage preamp, or is it one tube for each channel?

 

If it is a two (2) stage preamp, and I was standing behind the amp looking into it, would stage one (1) be the tube on my left or the tube on my right?

 

Thanks to all

  • Nick_Mattocks Best of the Best
    Nick_Mattocks
    9,065 posts since
    Mar 26, 2007
    Currently Being Moderated
    Oct 29, 2011 4:15 AM (in response to broadfca)
    Re: DT50 Preamp Tubes (one ot two stage preamp)?

    The two 12AX7/ECC83  tubes are not pre-amp tubes in the traditional sense.  They are both part of the power amp section. 

     

    One boosts the overall level of the pre-amp output to drive the EL34's and the other is used as an inverter.

     

    Nick

    • broadfca Just Startin'
      broadfca
      21 posts since
      Dec 1, 2010
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      Oct 30, 2011 3:57 AM (in response to Nick_Mattocks)
      Re: DT50 Preamp Tubes (one ot two stage preamp)?

      Thank you Nick, your timely response is very much appreciated. Here is the reason for my question:

       

      I play mostly BB King to SRV style music. So far I am very pleased with this DT50. However, the amp is capable of putting out way more distortion than I will ever want. So, I am interested in expirimenting with different tubes for the one that boost the overall level of the preamp output. (Such as the 12AT7EH and the 12AY7EH)

       

      Using my example of standing behind the amp looking in to it, with the amp right side up, would the boost tube be the tube on my right or the tube on the left.

       

      Thanks again for your help.

       

      Carl

      • spaceatl Expert Line 6 User
        spaceatl
        4,456 posts since
        Jan 24, 2007
        Currently Being Moderated
        Oct 30, 2011 7:46 AM (in response to broadfca)
        Re: DT50 Preamp Tubes (one ot two stage preamp)?

        The preamp type tubes in the DT50 are NOT preamp tubes...They are part of the power amp...The preamp is a digital modeler and all your preamp distortion is coming from there...

         

        12AT7 and 12AY7 are less gain than 12AX7, but changing them is NOT going to reduce the distortion potential of the preamp....It would likely subtley change the power amp repsonse...good or bad? I don't know...experiementing is the only way to know...

         

        I will have to go take a look at my DT50 112 as I am not sure if I am remembering this correctly...I have a GTSAG-AX7 in there...balanced inverter. I use an Mesa SPAX7 for the buffer tube.

         

        I think the one nearest the speaker jacks is the inverter....I think the head is backwards from the combos but I am not sure...That information is in the forum some place, I just could not located it...

        • broadfca Just Startin'
          broadfca
          21 posts since
          Dec 1, 2010
          Currently Being Moderated
          Nov 1, 2011 6:57 AM (in response to spaceatl)
          Re: DT50 Preamp Tubes (one ot two stage preamp)?

          Well...... this water is definitely deeper than my swimming skills are equiped for. Maybe I'll just leave it alone and enjoy waves.

           

          Switching gears a bit.... I just got a Pod HD300 to play with the Link 6 amp modeling features of this amp. This is probabaly a better path for me to find the tones I want.

           

          I was following the Advanced Guide to do the SETUP of the HD300. Everything was going just as the guide showed until I got to the AC rate options. I wanted to be sure it was set at 60Hz. The problem is, the AC rate wasn't there??? Everything else matched the guide exactly.... but NO AC rate showed at all. Any ideas as to why that would be?

           

          Also, am I correct in assuming that when using the Link 6 connection, that the Pod300 should be set for ComboAmp and NOT ComboFrt ?

           

          Lastly, does the Link6 cable need to be unpluged from the Pod300 before   updating via USB ?

           

          These are questions I haven't been able to find the answers to yet.

           

          Thanks for all your help

          Carl

          • spaceatl Expert Line 6 User
            spaceatl
            4,456 posts since
            Jan 24, 2007
            Currently Being Moderated
            Nov 1, 2011 7:25 AM (in response to broadfca)
            Re: DT50 Preamp Tubes (one ot two stage preamp)?

            Sounds like you need a firmware update for your 300...You can do that with a PC, USB cable and Line 6 Monkey...

             

            Likely, if you have not done it, your DT50 might need to be updated also...For that one you need a midi interface on your PC...You can pick up an M-Audio UNO USB-midi interface for around $30 or so...

             

            Yes, disconnect the link while updating...

             

            In terms of the mode, the most important is the Mode switch being in LIVE mode...I keep my soft output mode set to Combo PWR AMP on my HD400...

            • broadfca Just Startin'
              broadfca
              21 posts since
              Dec 1, 2010
              Currently Being Moderated
              Nov 5, 2011 7:18 AM (in response to spaceatl)
              Re: DT50 Preamp Tubes (one ot two stage preamp)?

              Is there any reason to update the DT50 if you're not using a Pod HD "500" ?

               

              I have the HD 300. Will a DT50 update be helpful in this case?

               

              Thanks,

              Carl

              • Nick_Mattocks Best of the Best
                Nick_Mattocks
                9,065 posts since
                Mar 26, 2007
                Currently Being Moderated
                Nov 5, 2011 7:24 AM (in response to broadfca)
                Re: DT50 Preamp Tubes (one ot two stage preamp)?

                Yes - I would say you should update as there may have been some minor changes made to the four on-board HD PRE amp models since your amp's firmware was released.

                 

                It's not mission critical that you do this if you aren't using a POD HD of course and if you are happy with your sound as-is you can leave updating alone for now, but nevertheless, me being me, I would update personally

                 

                Nick

                • broadfca Just Startin'
                  broadfca
                  21 posts since
                  Dec 1, 2010
                  Currently Being Moderated
                  Nov 7, 2011 4:10 AM (in response to Nick_Mattocks)
                  Re: DT50 Preamp Tubes (one ot two stage preamp)?

                  Thanks Nick, went ahead and did the amp update.

                   

                  I just recently got this amp used from ebay. I noticed yesterday, that when the master volume is turned to full volume, there is a low frequency hum.

                   

                  With both "channel" volumes turned all the way down, and the "master" turned all the way up.... when I start turning the channel volume up, as I progress to half volume the hum starts becoming clearly audible and gets a little louder as I progress to full channel volume. This happens on both channels, which ever channel the amp is set to ( the channel which is in use).

                   

                  Anyone have any ideas as to what might cause this?

                   

                  Thanks,

                  Carl 

                  • Nick_Mattocks Best of the Best
                    Nick_Mattocks
                    9,065 posts since
                    Mar 26, 2007
                    Currently Being Moderated
                    Nov 7, 2011 9:14 AM (in response to broadfca)
                    Re: DT50 Preamp Tubes (one ot two stage preamp)?

                    The bias settings might be slightly out of whack or perhaps the tubes need looking at.  However all valve amps emit a low level of background hum and it's normal, but this isn't usually very loud and the level of background hum doesn't normally increase when you turn the amp's volume controls up.  The problem with buying used is that you don't really have full knowledge of an item's history.  

                     

                    Does this hum present itself with nothing connected to the amp?   I'm just ruling out dodgy cables and ground loop issues.

                     

                    My gut feeling is telling me you should check the two ECC83/12AX7 valves and perhaps get an amp tech to check the bias of the amp for you.

                     

                    Nick

                    • broadfca Just Startin'
                      broadfca
                      21 posts since
                      Dec 1, 2010
                      Currently Being Moderated
                      Nov 8, 2011 4:57 AM (in response to Nick_Mattocks)
                      Re: DT50 Preamp Tubes (one ot two stage preamp)?

                      Thanks Nick. yeah, the amp does this with nothing hooked up to it. That was the first thing I checked. It acts the same with or without my hd300 connected vis L6.

                       

                      I replaced the 12AX7's with new tubes. That cut down the hiss and noiseiness of the amp considerably, but the hum is still there. From what I'm hearing, a little hum is ok except that it shouldn't get louder as you turn up the volume knobs, as mine does.It's not what I would call a loud hum, and it doesn't project through the guitar sound when I play, but when you stop playing, you can hear the amp sitting there with a low hum coming from it.

                       

                      Guess I need to find an authorized repair center. However, at lower volumes, below half way, it sounds really good and the hum is not really noticible.

                       

                      Thanks again Nick

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