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Another Silvertone 1484 tremolo even without tremolo!!!

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  • #1

    Another Silvertone 1484 tremolo even without tremolo!!!

    Hi guys hope all is well this morning.

    So I have been working on rebuilding a silvertone 1484 for a week now and everyday has been a breakthrough! HOwever I am stumped now:

    I just finished replacing the (4) 100uF filter caps and the 100uF cap for the bias supply. Everything works great now except i am getting some serious noise issues. I suspect them to be coming from the preamps.

    Channel 1: as i gradually turn the volume up i get a high pitched squeal that eventually turnes into a nice LF hum about 2/3rds the way up.

    Channel 2: nasty hum all the way through and the hum is even being tremoloed when I engage that! sounds like 60hz hum with a surf vibe!

    Anyway, I suspect that the caps in the preamp section will need be replaced at this point. My main objective is to just get the damn thing playable with as little effort as possible.

    Does anyone have any advice as to a potential first direction to take?? I appreciate everyones help here!
    Tags: 1484, silvertone
  • #2
    Is there a metal shield behind the control panel, between the power tubes and the panel? Is it installed or removed?

    I ask because in some SIlvertone models it is ther, and without it, the power tubes radiate into the preamp, and the amp oscillates. From your description, I suspect your amp is oscillating. This oscillation occurs at frequencies way above audio. But when it occurs, since the amp is working so hard to produce it, you hear a sort of soft hum through the speakers. And often the sound of the guitar will be kind of dull and lifeless, with maybe increased general noise.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      My test today supports that thought....

      This amp does NOT have the said shield, however the power transformer is in that place, which I understand has a magnetic field of its own. Curiously though, the 12ax7 that powers the tremolo circuit is directly behind the two 6l6's, opposite to the rest of the preamp tubes.

      As far as my test today, i dont know if what I did has any validity to my issue, but I took two jumper wires today and connected them to the positive (tip) of each channel input to see what would happen:

      when connected to chassis ground, the buzz/hum/oscilation goes away. In thoery, this makes sense i think.

      however, more interestingly, when i disconnected the jumper from the ground hort and waved it around in the air, I go all sorts of fun noise almost like a theriman. I could get a theriman sound by waving the jumper wire around in the air....which to me, would support your idea Enzo.

      So with that being said, any suggestions to eliminate or filter this magnetic/rf interference? Here is a link to the schematic:
      http://www.freeinfosociety.com/elect...ertone1484.pdf

      If it would be beneficial to my objective (get the amp clean and playable) I am not opposed to bypassing or eliminating the tremolo and/or reverb cicuit

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      • #4
        Mine does not have a metal shield either. I even tried putting one on and it did nothing.

        If all you did was replace the 100uf caps to cause this upset then re-check caps polarity... or maybe you got a bunk cap. First check the caps before anything.

        Tremolo doesn't need to be bypassed. Just use the first channel.

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        • #5
          Then you solved it. Does plugging a guitar into it stop the noise? Install shorting jacks at the inputs. The schematic shows open circuit jacks, but possibly shorting jacks are in it, just not wired that way.

          Put a shorting jack in the left jack spot for each channel, leave the right jacks alone. That way, when you plug into the left jack, you get full gain, when you plug into the right jack, the two 68k resistors drop the signal level 6db.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Shorting Jacks are the answer!! Thanks Enzo that does it. When guitar is plugged in noise noise away.

            New problem uncovered however, now when adjusting treble tone control, about 3/4 of the way up, the signal turns into a squeal. Of course, I suspect the caps in the tone filter so they will get replaced today.

            One question though: C8 and C9 are labeled as "680 UUF" on schematic. I have never seen "UUF" before. Is this something unique and special or just another misprint on the scheme?

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            • #7
              Google time....

              Originally posted by jzproductions View Post
              One question though: C8 and C9 are labeled as "680 UUF" on schematic. I have never seen "UUF" before. Is this something unique and special or just another misprint on the scheme?
              Right on a quick google search and I have been learned up!

              uuF=micromicro farads which is the same as pf or pico farads

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              • #8
                On even older drawings it would have been mmf.
                Education is what you're left with after you have forgotten what you have learned.

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