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Fender Red Knob Twin questions

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  • #1

    Fender Red Knob Twin questions

    Hi all....help....as soon as the tubes warm up I have to turn it off, because the hum is Soooooooooooooo LOUD you can hear it a mile away !!!

    Problems found...R56...burned around middle but still reads and...R121...........( CB10F-3K-10% )...overheated and doesn't read at all, but R128 still reads 2.7K.

    Could these cause amp to make VERY VERY loud hum as soon as it is fired up? I don't want to leave it on because I am afraid the loud hum might ruin the speakers or blow a wall out of my shop !!! No guitar or guitar cord is pluged into amp.
    The reverb knob ( in front of R56 ) has been broken off and the bass knob for Ch. 2 is bent a little.

    I pulled the two middle 6L6's and the noise went away but the next day the noise was back...even with the middle tubes removed.

    Sewing machines and vacuums I know but I am a newbee for sure with amps.
    Thanks in advance for some professional and/or personal advice. I have been doing some homework....reading and reading......yes, as you can tell....the Amp Bug has bitten again.

    I really appreciate this Forum........your knowledge and willingness to help others who enjoy the wonderful world music is amazing! Thanks.
    Doc Stitches
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  • #2
    R121 is the ground reference for the negative feedback to the phase inverter. You need to replace it. It would definitely cause the hum. R56 is the cathode resistor for the reverb driver tube. Also could cause hum if open. If shorted would be bad for V8
    Warning! Some Electronics devices contain lethal voltages that can kill you. If you do not feel qualified to work with dangerous voltages, refer your repairs to a qualified technician. By giving you online advice, I am assuming no liability for any injury or damages you might incur through your own actions.

    Comment

    • #3
      It's possible those output tubes are mismatched. Swap them and see what happens.

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      • #4
        Seeing as this hum will come and go, I'd look for loose components, bad solder connections and broken wires. I think that when you pulled the two center tubes you caused something to make connection, but it has broken again.

        If you do an Enzo thump (whack the top of the amp with your fist), does it cause the hum to start or stop?

        Comment

        • #5
          Happy Red Knob Twin in Santa Cruz.

          Thanks for the fast responses. All were appreciated.....I replaced R121 and R56 and I now have a great sounding Fender Twin with good reverb. .....Where can I get :

          1 reverb pot
          2 pull/push bass pot ...local shops don't have them
          3 a schematic that I can read,,,,,,,the internet photocopies are just too fuzzy
          is the one from Fender Company any better?

          Thanks again for everyones help. You are appreciated here in " Newbee Land. "
          If you ever need sewing machine help just call me. My number is on my website : sewingmachinerepair.com

          Jim

          Comment

          • #6
            here is the schematic. I'll get back to you on the parts.
            Attached Files
            Warning! Some Electronics devices contain lethal voltages that can kill you. If you do not feel qualified to work with dangerous voltages, refer your repairs to a qualified technician. By giving you online advice, I am assuming no liability for any injury or damages you might incur through your own actions.

            Comment

            • #7
              Originally posted by Doc Stitches View Post
              Happy Red Knob Twin in Santa Cruz.

              Thanks for the fast responses. All were appreciated.....I replaced R121 and R56 and I now have a great sounding Fender Twin with good reverb. .....Where can I get :

              1 reverb pot
              2 pull/push bass pot ...local shops don't have them
              3 a schematic that I can read,,,,,,,the internet photocopies are just too fuzzy
              is the one from Fender Company any better?

              Thanks again for everyones help. You are appreciated here in " Newbee Land. "
              If you ever need sewing machine help just call me. My number is on my website : sewingmachinerepair.com

              Jim
              Did you manage to get the parts for your twin? I have the name of a supplier if not......

              Comment

              • #8
                Hi Mouse. I would like the name of a supplier for the parts.

                Thanks
                Jim

                Comment

                • #9
                  Originally posted by Doc Stitches View Post
                  Hi Mouse. I would like the name of a supplier for the parts.

                  Thanks
                  Jim
                  I got the volume pots from these guys....

                  http://www.tubeampdoctor.com/index.p...d97b0d2dc15215

                  Couldn't get a pot in the uk through Fender or anyone - so wrote an e-mail to Fender Customer Service , they gave me the "proper" part number, stuck it in google and these guys came out.... Got the part within a few days from usa to uk and hey presto a have a happy red knobbed twin again. Which FYI I have had from new and would not swap for any other amp, Have had a few complete re-valves, the knob broke off because I dropped it putting it my car, and the reverb pot needed a re - solder - which I did myself.... and thats about all its had done to it..

                  Comment

                  • #10
                    The great Red Knob

                    Thanks again.

                    I agree with your evaluation of the Red Knob Twin. It has an unbelievable sound quality. I think they are a GOLD MINE waiting to be descovered.

                    Jim

                    Comment

                    • #11
                      Originally posted by mouse View Post
                      I got the volume pots from these guys....

                      http://www.tubeampdoctor.com/index.p...d97b0d2dc15215

                      Couldn't get a pot in the uk through Fender or anyone - so wrote an e-mail to Fender Customer Service , they gave me the "proper" part number, stuck it in google and these guys came out.... Got the part within a few days from usa to uk and hey presto a have a happy red knobbed twin again. Which FYI I have had from new and would not swap for any other amp, Have had a few complete re-valves, the knob broke off because I dropped it putting it my car, and the reverb pot needed a re - solder - which I did myself.... and thats about all its had done to it..

                      These are good to....

                      https://www.musicpartsguru.com/thumbnail.asp?cid=27

                      Comment

                      • #12
                        Im experiencing some crackling noise and loss of sound when the amp goes into play mode after 45 secs in standby. Is it choke or else???

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