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Screaming Bright Switch Cap??? - 1974 Fender SF Twin Reverb Master Volume Push Pull Switch

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  • yes! thank you guys... i think that the quest for knowledge and customization to own taste is a long, winding and uphill road
    i agree that after unsuccessfully looking for the photoresistors i will buy the ”mysterious roach”

    Comment


    • Never hurts to ask a manufacturer for 'samples' either. The worst case is they say no.
      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

      Comment


      • Hi all,
        got the new "roach" and installed it. Tremolo is deeper now.

        Comment


        • Hi all,

          I have a new question (yes, I know what you are thinking... LOL) regarding this project after watching the video (link below) of a work performed on a 135W Fender Twin that had the MASTER switch removed together with the PULL BOOST function.

          As a reminder, I have removed the PULL BOOST wiring from the circuit a while ago (I kept the MASTER VOLUME) at the time I had that strange SCREECH sound that ended up being caused by incorrect lead dressing on the V1 channel.

          I removed the wiring as marked in RED in the following schematic.



          The question comes after the suggestion made in the video of removing 3 components (marked in YELLOW) that apparently only have a reason to be there for the PULL BOOST function. This is explained as follows 25m34s into the video

          "to finish the clean up after the removal of the shielded cable (...) we are going to remove the 12K resistor, the .01 uF cap and the 1 M resistor to ground. This is no longer needed. the reason (...) is that this is a grounded line and we do not want it to be able to interfere with the passage of our signal from the plate of V4B to the phase inverter"



          My concrete questions:

          - Is that right? the 3 components need to be removed
          - from a theoretical point of view, what do you guys expect to happen? what difference should I hear after removing them?

          thx!!!

          Comment


          • Take 'em out! You can always put them back in, right? Here's the thing... You've already had some trouble with stability in this project and that network DOES introduce a small low pass filter. If the area that's that those components are located in does not affect the stability of the amplifier then I would consider it a positive thing to be rid of them. There's nothing to lose in trying as long as you can undo what you did

            P.S. The trem on that amp in the video sounds like @$$. All garbled and distorted. I wouldn't be chasing that video as a tonal standard to aspire to otherwise either. But now I'm just being a wet blanket.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

            Comment


            • Originally posted by Chuck H View Post
              Take 'em out!
              that's all i needed to hear ... LOL

              Originally posted by Chuck H View Post
              The trem on that amp in the video sounds like @$$. All garbled and distorted. I wouldn't be chasing that video as a tonal standard to aspire to otherwise either. But now I'm just being a wet blanket.
              I'm with you, however I think everything on that video sounds bad and I am thinking is the camera's mic being unable to handle the powerful twin

              Comment


              • that network DOES introduce a small low pass filter
                Yes, cuts treble above 16kHz.
                - Own Opinions Only -

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                • danke! i should not hear a difference if everything happens above 16KHz.

                  actually here's an easy side by side comparison on how the circuit looked like during the evolution from the ONLY MASTER VOLUME version (010182 RevC) to the addition of the PULL BOOST (45377 RevE).
                  It's clear that that arrangement (12K, .01uF, 1M) is not there in the ONLY MASTER VOLUME version
                  however, additionally there is a 1K resistor that is also not there
                  the landmarks I used to identify the common components are marked in GREEN and the differences in RED

                  I guess that now the complete question is: should i remove: 12K, .01uF, 1M AND the 1K resistor?

                  Comment


                  • I don't suspect that area of the amp and it's circuitry in your previous problem. I doubt you'll hear a difference. You can simply lift one end of any of those components to see if it makes any difference for yourself. But to ask us if you "should" isn't something we can answer because the amp is not on any of our benches. I think you should try because the idea seems to please you. If it causes a problem you can put them back.
                    "Take two placebos, works twice as well." Enzo

                    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                    Comment


                    • AND the 1K resistor?
                      The 1k resistor just adds to the 470k, resulting in 471k +/- 10%.


                      should i remove: 12K, .01uF, 1M
                      This HF filter may even have a beneficial effect, as it will attenuate residual oscillation blips. So best try both ways as Chuck recommends.





                      Is there still a problem with the amp?
                      Last edited by Helmholtz; 01-16-2020, 07:27 PM.
                      - Own Opinions Only -

                      Comment


                      • Originally posted by Helmholtz View Post
                        Is there still a problem with the amp?
                        I think there's not... but I will only know if I remove these components and find out it sounds better! LOL
                        + you're totally right about the 417K

                        Comment


                        • Agree with Helmholtz that the circuit could 'accidentally' help prevent oscillations above 16khz so keep this in mind if anything weird happens with it gone.
                          As a side note, since you just worked on the trem; not sure if I mentioned this already but this era Fender sometimes has the shielded cables dressed very close to the trem bug, and it can have quite an impact on the trem 'ticking' problem.
                          "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                          Comment


                          • yes! I had that problem in the past with the tremolo and fixed it by adding the .022 uF cap tremolo tick fix (which was actually a fix Fender came up with)
                            thx!

                            Comment


                            • Ok, I mentioned that for the cases where the cap fix doesn't get rid of it all.
                              "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                              Comment

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