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Changing Plate resistor question.

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  • #16
    Thanks Dave.
    So I guess I'm back to wondering how I make this thing overdrive a bit more when I wind the gain knob up....

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    • #17
      How about a pedal out in front?

      A simple 'boost' pedal should do it.

      Or a Tube Screamer.

      Comment


      • #18
        Originally posted by Shawnobi View Post
        Thanks Dave.
        So I guess I'm back to wondering how I make this thing overdrive a bit more when I wind the gain knob up....
        With a complement of 3 each 12AX7s, I'm guessing that your amp uses 1 for the PI, and the other two are used for gain functions - but that may not be the case. Without knowing exactly what the signal flow through the amp looks like, we're all blind men poking at an elephant. Changing a resistor can make drastic (that is to say, noticeably audible) differences in an amp's gain, but it has to be the *right* resistor in the *right* location. As has been posted above, the resistors at the plate or cathode of stage 1 or 2 can have an effect on the sound, but it won't take an amp from clean to crunchy, and may not even be the effect you're looking for.

        A drawing that shows the signal flow through the preamp tubes, with the plate and cathode component values, AND any interstage divider component values, AND the tone stack, will go a long way to bringing the issue you propose here into the light.

        Many amps will have a "boost" function that is nothing more than a component that bypasses some or all of the tone stack, allowing a substantial increase in gain. The best part of that is it can be put on a switch!
        If it still won't get loud enough, it's probably broken. - Steve Conner
        If the thing works, stop fixing it. - Enzo
        We need more chaos in music, in art... I'm here to make it. - Justin Thomas
        MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

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        • #19
          I'm tempted to build a tubecaster. My problem is that I'm a compulsive tinkerer. I like the idea of tuning the amp rather than adding additional hardware. Also modifying will help my understanding of how amps work.

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          • #20
            Originally posted by Shawnobi View Post
            I'm tempted to build a tubecaster. My problem is that I'm a compulsive tinkerer. I like the idea of tuning the amp rather than adding additional hardware. Also modifying will help my understanding of how amps work.
            I have a prototype head amp that is not in a case, that I experiment with.
            If you are going to change the preamp components often, I would use a Turret board.
            They are the easiest to change resistors and caps on.
            I'm changing and adding Cathode bypass Caps all the time when I'm looking for a particular sound.
            Good Luck,
            T
            "If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
            Terry

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            • #21
              Originally posted by eschertron View Post
              With a complement of 3 each 12AX7s, I'm guessing that your amp uses 1 for the PI, and the other two are used for gain functions - but that may not be the case. Without knowing exactly what the signal flow through the amp looks like, we're all blind men poking at an elephant. Changing a resistor can make drastic (that is to say, noticeably audible) differences in an amp's gain, but it has to be the *right* resistor in the *right* location. As has been posted above, the resistors at the plate or cathode of stage 1 or 2 can have an effect on the sound, but it won't take an amp from clean to crunchy, and may not even be the effect you're looking for.

              A drawing that shows the signal flow through the preamp tubes, with the plate and cathode component values, AND any interstage divider component values, AND the tone stack, will go a long way to bringing the issue you propose here into the light.

              Many amps will have a "boost" function that is nothing more than a component that bypasses some or all of the tone stack, allowing a substantial increase in gain. The best part of that is it can be put on a switch!
              I'd love a scheme for this thing! It's quite hard to draw my own from the PCB, things get quite confusing. I understand what you are saying though, I'm just a typical Mod-Newbie wanting the moon on a stick It does have a boost switch. I should look into the circuit that is on.

              Big-Teee - Not a bad idea. I have a fear of track lifting on the PCB if I start pulling components in and out quite often.

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              • #22
                For reference - here she is with a few 'beautification' mods!
                Click image for larger version

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                • #23
                  I've taken the liberty of redrawing your partial schematic here.

                  I'd love a scheme for this thing! It's quite hard to draw my own from the PCB, things get quite confusing.
                  When you get back in there, there should be a capacitor connected to the first plate (pin 6) and R3. I've labelled where that should go "A" on my schematic.

                  Try to get as far as connecting point "A" to point "B" and we should have much better info for you.

                  While you're at it, jot down the voltages at the tube terminals too.
                  Attached Files

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                  • #24
                    That's really kind of you, thank you. I should have chance to open it up tomorrow evening with a bit of luck.

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                    • #25
                      Originally posted by Shawnobi View Post
                      For reference - here she is with a few 'beautification' mods!
                      [ATTACH=CONFIG]26524[/ATTACH]
                      regardless, she looks like a beauty!

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                      • #26
                        Here we go. FYI C3 is a 100pF Ceramic disc capacitor.


                        Click image for larger version

Name:	Subzero Pre.jpg
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ID:	831864

                        Kingsway Guitar - Thank you
                        Last edited by Shawnobi; 12-03-2013, 06:57 AM.

                        Comment


                        • #27
                          Here's the schematic for the Strauss SVT-H50R. See if it matches your subzero.
                          Attached Files

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                          • #28
                            Originally posted by dwmorrin View Post
                            Here's the schematic for the Strauss SVT-H50R. See if it matches your subzero.
                            Amazing! I tried Strauss but never got a reply. That certainly looks the same. Its even stamped Belcat which is the other brand its sold under. Thank you.

                            Comment


                            • #29
                              There's an unused 12AX7 gain stage! Tinkerer's heaven!

                              'I have a fear of track lifting on the PCB if I start pulling components in and out quite often'

                              Consider fitting small turrets/solder pins into the pcb holes, once components are removed.
                              Then the trial replacement parts can be easily fitted and swapped out, all done on the component side of the board, with minimal stress to the pad / track.
                              Pete
                              My band:- http://www.youtube.com/user/RedwingBand

                              Comment


                              • #30
                                Originally posted by pdf64 View Post
                                There's an unused 12AX7 gain stage! Tinkerer's heaven!

                                'I have a fear of track lifting on the PCB if I start pulling components in and out quite often'

                                Consider fitting small turrets/solder pins into the pcb holes, once components are removed.
                                Then the trial replacement parts can be easily fitted and swapped out, all done on the component side of the board, with minimal stress to the pad / track.
                                Pete
                                I've got some breadboard type turrets at work.

                                I noticed that V2B seemed to be empty. So how do I best rope that gain stage in to my preamp circuit? That could be exactly what I'm looking for!

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