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Simms Watt 100w Head

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  • #31
    The next pictures are with all valves on again.

    First with the bulb connected directly to the wall. That's how it looks normally, you can look at it just for a moment, but not pleasant at all. Just a normal bulb on.

    Click image for larger version

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    Next a picture of the bulb with the amp connected, just mains ON. You can look at the bulb quite ok, no sunglases needed.

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    Not sure how useful the pic is because the amps are so different. But anyway here's another pic of the limiter when connected to a working 100w Marshall Valvestate.

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    -----

    Regarding the amp bulb yeah I cannot see it in the schematics either. I did more tests around it.

    When the amp was with all the valves on it didn't light up at first. With a wooden stick I hit here and there around the area where the diodes and bias cap are, and then it lighted up, not full light but clearly visible on. Sometimes it would go off and then on after hitting again.

    I took the valves out again and the bulb in the amp lights up normally, I can hit around with the stick and it just stays on.

    At least I guess I should take that part out and re-solder it again.

    ------

    One thing I've done every time I've switched it on is checking the bias capacitor, to see if there was any voltage stored in it. I haven't been able to get any readings from it so far. That cap is among the ones I have replaced.

    ------

    josegrad should (carefully, DEADLY voltage there) measure voltage with Standby OFF, just before the switch.
    I'm sure I can do it safely but didn't measure that. I'm not sure where to place the probes. You mean just before the second switch? I know one of the cables is a red one in the switch, but now sure where the other probe should go.

    Click image for larger version

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    PS: I appreciate your comments. Maybe I'll end up having to take it to a pro, but so far I'm having fun with the process and trying it myself. I hope you are not getting bored with these newbie questions.

    Comment


    • #32
      Originally posted by josegrad View Post
      One thing I've done every time I've switched it on is checking the bias capacitor, to see if there was any voltage stored in it. I haven't been able to get any readings from it so far. That cap is among the ones I have replaced.
      The voltage should be at the negative (-) end of that cap, and should be a negative DC reading.

      I'm sure I can do it safely but didn't measure that. I'm not sure where to place the probes. You mean just before the second switch? I know one of the cables is a red one in the switch, but now sure where the other probe should go.
      Black probe to ground, red probe to standby switch. First try one side of switch, if nothing check the other side. Should be +400VDC or more.
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


      Comment


      • #33
        "When the amp was with all the valves on it didn't light up at first. With a wooden stick I hit here and there around the area where the diodes and bias cap are, and then it lighted up, not full light but clearly visible on. Sometimes it would go off and then on after hitting again.

        I took the valves out again and the bulb in the amp lights up normally, I can hit around with the stick and it just stays on.

        At least I guess I should take that part out and re-solder it again."


        That sure soumds like a bad connection to me...

        Justin
        "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
        "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
        "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

        Comment


        • #34
          Here's the voltage at the second switch.
          No valves btw.

          Without hands...

          Click image for larger version

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          The reading:

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          Last edited by josegrad; 11-03-2018, 09:01 PM.

          Comment


          • #35
            Originally posted by Justin Thomas View Post
            "That sure sounds like a bad connection to me...Justin
            Agree, I will re-solder that part of the amp.

            Comment


            • #36
              Originally posted by josegrad View Post
              Agree, I will re-solder that part of the amp.
              This may be oxidized contacts and not bad soldering. Is it a screw-in bulb, a twist-in Bayonette-type bulb, or one with a pair of pins..plug-in bulb? Any of these, you need to scrub the contacts of both the bulb and the socket(s). Oxidation never sleeps.
              Logic is an organized way of going wrong with confidence

              Comment


              • #37
                Originally posted by nevetslab View Post
                Oxidation never sleeps.
                Yep, in any case I guess I need to take that part out and check those contact I guess.
                I'll be traveling 3 days so I'll do it when I get back.

                Btw I was advised to take the voltage just before the second switch, which was 388 VDC.

                Comment


                • #38
                  I re-soldered that part, and replaced the bias cap, I originally got a new one of 47uF 500VCD, and now I have one of 47uF 200VDC which closer to the one that was on the amp.

                  Now the light bulb lights just a bit and then remains almost invisible.

                  But when I place all the valves again then the light bulb lights. Not full brightness but much brighter than without the valves.
                  I guess I should buy new valves and see what happens.
                  Last edited by josegrad; 11-10-2018, 06:57 PM.

                  Comment


                  • #39
                    That limiter bulb activity sounds perfect. It lights a bit as the cap is charging with inrush current and then the current subsides once the caps are charged. So something you did corrected a short or partial short

                    You should confirm bias voltage on the power tube sockets before installing tubes. Just because you were soldering in the circuit it's good to check that nothing is shorted, open or miswired because the bias voltage being present is critical.
                    "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

                    "If you're not interested in opinions and the experience of others, why even start a thread?
                    You can't just expect consent." Helmholtz

                    Comment


                    • #40
                      Originally posted by Chuck H View Post
                      You should confirm bias voltage on the power tube sockets before installing tubes.
                      Just wondering how much that voltage should be.
                      I guess I should measure voltage on all 4 valves right?

                      UPDATE

                      There is a wrong and worst, bad resistor on the second valve socket. I'll need to start by replacing that one.
                      Last edited by josegrad; 11-10-2018, 08:31 PM.

                      Comment


                      • #41
                        Which resistor?

                        On the schematic you provided someone has written -50 near the bias circuit. That seems a little high to me, but the bias circuit looks to be adjustable so perhaps that's the max range. If your voltage is still 388V unloaded I would expect bias voltage at -40V or less. But MORE bias is still perfectly safe and you should adjust the voltage relative to current through the tubes.
                        "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

                        "If you're not interested in opinions and the experience of others, why even start a thread?
                        You can't just expect consent." Helmholtz

                        Comment


                        • #42
                          Originally posted by Chuck H View Post
                          Which resistor?
                          The second resistor. I can't get any reading from it, besides it is not the right value.

                          Click image for larger version

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                          It should be 270 ohm, but I can only find this one here at hand, not CCR:
                          https://en.uraltone.com/electronic-c...70-ohm-1w.html

                          CCR I can find 330 or 220 omh.

                          Not sure if CCR or not would make any difference.


                          Originally posted by Chuck H View Post
                          ...you should adjust the voltage relative to current through the tubes.
                          Ok, so I guess you mean I should measure the input voltage that gets into the tubes.

                          Comment


                          • #43
                            Originally posted by josegrad View Post
                            The second resistor. I can't get any reading from it, besides it is not the right value.

                            [ATTACH=CONFIG]51061[/ATTACH]

                            It should be 270 ohm, but I can only find this one here at hand, not CCR:
                            https://en.uraltone.com/electronic-c...70-ohm-1w.html

                            CCR I can find 330 or 220 omh.

                            Not sure if CCR or not would make any difference.




                            Ok, so I guess you mean I should measure the input voltage that gets into the tubes.
                            I'm pretty sure those red ones are Flameproof 3 watt resistors. Not Carbon comp
                            Where is your location at?
                            nosaj
                            soldering stuff that's broken, breaking stuff that works, Yeah!

                            Comment


                            • #44
                              I'm in Finland...

                              Based on the schematic those should be 270 ohm 1 watt.

                              Click image for larger version

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                              Can't say for sure what's on the amp, but I've seen other pictures of the same amp and I think they are the originals.

                              Is it a big issue using the ones I found?

                              Comment


                              • #45
                                Originally posted by josegrad View Post
                                I'm in Finland...

                                Based on the schematic those should be 270 ohm 1 watt.

                                [ATTACH=CONFIG]51062[/ATTACH]

                                Can't say for sure what's on the amp, but I've seen other pictures of the same amp and I think they are the originals.

                                Is it a big issue using the ones I found?
                                probably not but there is a mouse in Europe more variety I'd imagine
                                https://www.mouser.com/cs/LocalSites...qNgv4tzkKqrFRG
                                nosaj
                                soldering stuff that's broken, breaking stuff that works, Yeah!

                                Comment

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