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New Tremolux 5G9 build --> input welcome!

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  • #76
    I used 2.5MRA (actually a dual-gang 5MRA with the gangs in parallel) with 120k from the wiper to ground (like the 5G9), and the trem starts to kick in at about 1. 3Hz sounds about right.

    I think the only place you would find one of those 2M pots these days is in a vintage 5G9 or 5E9A
    Building a better world (one tube amp at a time)

    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

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    • #77
      Originally posted by tubeswell View Post
      I used 2.5MRA (actually a dual-gang 5MRA with the gangs in parallel) with 120k from the wiper to ground (like the 5G9), and the trem starts to kick in at about 1. 3Hz sounds about right.

      I think the only place you would find one of those 2M pots these days is in a vintage 5G9 or 5E9A
      Thanks a lot for checking! I have been thinking why the trem kicks in too late in my amp.

      Here are some calculations that might possibly explain the situation. I think the actual resistance evolution of my 3M RA pot is not 'ideal' and therefore there is the (huge) offset. See the following graph (there is first a flat bit that causes an offset before it starts to fall sharply).

      Click image for larger version

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      At about 1.5 MOhm resistance the trem kicks in at my amp. With the CTS 3M RA (or antilog) pot that I used, 1.5MOhm is at dial position 4. It should kick in much earlier. Both by the offset in 3 Mohm versus the original 2M and the non-ideal anti-log evolution (flat bit in the beginning) of my pot, there is a huge offset in reaching the 1.5MOhm.

      I think when you would measure the actual resistance when the trem kicks in I bet it is around 1.5MOhm as well. Maybe your antilog pot has a better, more ideal curve?

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      • #78
        Tremolo speed issue: solved!

        I have spent some time (again) looking into why there is the offset in the tremolo speed (it kicks in at speed dial position '4' at a frequency of about 3.5Hz).

        1) I have put the 220uF parallel to the 25uF in the tremolo circuit, like loudthud suggested. The speed is only a bit slower (about 3Hz), BUT it starts to kick in at dial position 5, so even a larger offset...
        2) I have tried different tubes for v3 (with the 220uF still parallel to 25uF). All 12ax7's that I tried gave the same results. When going to 12at7 (NOS Mullard), the tremolo kicks in above 7 and a 12ay7 doesn't do anything at all - no tremolo effect.

        Then I unplugged the footswitch (for the first time since the build).............. Instant tremolo at dial position 1. I have a footswitch with LED indicator. When engaged there is a 1k resistor for the LED that causes all the trouble!

        Now the tremolo is excellent. Together with the 220uF in parallel to the 25uF and 0.01uF - 0.022uF - 0.047uF caps, I count a frequency of about 2.2 Hz (about 22 counts in 10 seconds). Without the 220uF it's about 2.8Hz... And the sound: it's nice, very nice!! It's almost too much to dial up the intensity all the way...

        So tubeswell: now I can understand that changing the 100k (or 160k that I am using) makes a difference also in the low speed area!
        Last edited by klooon; 05-06-2012, 06:58 PM.

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        • #79
          Yeah I use 120k with the 2.5MRA and it works fine
          Building a better world (one tube amp at a time)

          "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

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          • #80
            Personal forgive me if doing a dumb question, but where are the attachments and layout?

            I'm curious to see this layout ...

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            • #81
              Many attachments that were stored as part of the Music ELectronics Forum (posts from January 2010 to April 2013) were lost due to some kind of virus attack. Attachments hosted on other sites were not affected but may have been deleted or moved. I suggest that you PM the author. They can re-post the attachment or possibly just send you a copy.

              See this thread: http://music-electronics-forum.com/t34134/
              WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
              REMEMBER: Everybody knows that smokin' ain't allowed in school !

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              • #82
                Please find attached the latest/final version of the layout and a gut shot. Unfortunately, due to a hard disk crash, all other versions were lost.

                Click image for larger version

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                Click image for larger version

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                The Tremolux is still going strong. I have put a Weber 12A150A - great. I am only considering to change the tonestack to get a bit more highs/treble and less bass in to cut through when playing very loud with my humbuckers... The INSTR channel is a bit brighter, but not enough. I think I will use these recommendations: http://music-electronics-forum.com/t...47/#post205947
                Last edited by klooon; 11-18-2013, 08:16 PM.

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