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Thread: 68 Twin Reverb vibrato not working

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    68 Twin Reverb vibrato not working

    just replaced all electrolytic caps in this amp. It sounds good - everything works except vibrato, but I can hear a faint ticking sound when vibrato is on; speed varies when I adjust it - just no vibrato added to the amplified signal.

    I'm about to open the amp up again - if anyone has any insights as to what the problem may be, I'd appreciate it.

    thanks - Jim

  2. #2
    Forum Member DanTheBluesMan's Avatar
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    Re: 68 Twin Reverb vibrato not working

    welcome to teh forum, I'm not quite up to snuff yet on this kind of stuff but we have lots of guys who are. I'm sure they'll help get this sorted out right quick. Kudos for going under the hood, I'm good with a soldering iron but know too little about the goezintos and goesouttas of the amp circuitry ... yet. I'll be looking forward to hearing ... er, reading about this one.
    "Live and learn and flip the burns"

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    Forum Member vinyl's Avatar
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    Re: 68 Twin Reverb vibrato not working

    Welcome to the forum.

    Normally, I would be asking if you're using a footswitch, but since you're getting ticking sounds, The oscillator is trying to work.
    The next easiest thing to try is swapping V1 and V5.
    If that doesn't work, then the "trem roach" probably needs to be replaced. The "trem roach" is a simple optoisolator consisting of a neon bulb, and a light dependent resistor.

    Cheers,

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    Re: 68 Twin Reverb vibrato not working

    Quote Originally Posted by DanTheBluesMan View Post
    welcome to teh forum, I'm not quite up to snuff yet on this kind of stuff but we have lots of guys who are. I'm sure they'll help get this sorted out right quick. Kudos for going under the hood, I'm good with a soldering iron but know too little about the goezintos and goesouttas of the amp circuitry ... yet. I'll be looking forward to hearing ... er, reading about this one.
    thanks for your post. I suspect the opto-coupler - aka ‘roach’ - is weak. It;s the original one in the amp, which is now52 years old. Funny thing is that it worked a couple of days ago.

    Jim

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    Re: 68 Twin Reverb vibrato not working

    Quote Originally Posted by vinyl View Post
    Welcome to the forum.

    Normally, I would be asking if you're using a footswitch, but since you're getting ticking sounds, The oscillator is trying to work.
    The next easiest thing to try is swapping V1 and V5.
    If that doesn't work, then the "trem roach" probably needs to be replaced. The "trem roach" is a simple optoisolator consisting of a neon bulb, and a light dependent resistor.

    Cheers,
    Vinyl - thanks. Voltages all check OK, except on the varistor side of the roach. Since it’s 52 years old, I suspect that’s the problem. I’lll keep you posted. Should be several days before a new one arrives and I can install it.

    JIm

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    Re: 68 Twin Reverb vibrato not working

    I replaced the roach today and the vibrato is working again. Guess I can’t be upset that a 52-year old part failed.

    I’m just blown away by how good the Fender vibrato sounds - so slow and deep.

    Jim

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    Forum Member vinyl's Avatar
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    Re: 68 Twin Reverb vibrato not working

    Quote Originally Posted by conaway2 View Post
    I replaced the roach today and the vibrato is working again. Guess I can’t be upset that a 52-year old part failed.

    I’m just blown away by how good the Fender vibrato sounds - so slow and deep.

    Jim
    Thanks for coming back and letting us know how you fixed it. That doesn't always happen around here.

  8. #8
    Forum Member DanTheBluesMan's Avatar
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    Re: 68 Twin Reverb vibrato not working

    yes, i learned something from this thread. I happen to like Twin Reverbs, they're one of my bucket list amps. I often use them in stores to test out guitars.
    "Live and learn and flip the burns"

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    Re: 68 Twin Reverb vibrato not working

    Quote Originally Posted by DanTheBluesMan View Post
    yes, i learned something from this thread. I happen to like Twin Reverbs, they're one of my bucket list amps. I often use them in stores to test out guitars.
    I’m fortunate to own two Twin Reverbs - the ‘68 and a ‘72 with master volume control - in addition to a ‘66 Super Reverb that I bought when I was 15. I used to always take the SR to gigs, but have recently started taking one of the TR’s instead - since they have casters and are easier to lug around. As I get older, I believe these amps are gaining weight !

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    Forum Member Don's Avatar
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    Re: 68 Twin Reverb vibrato not working

    I've replaced quite a few roaches in recent years. Another thing that I've seen is a failed ceramic disc capacitor in the tremolo circuit. On one customer's '66 Vibrolux Reverb (an almost exact twin of mine), I noticed that the tremolo didn't come on right away- it needed time to "warm up"! One of the three ceramic disc capacitors was shiny with black spots on it. I replaced it and the tremolo was fine.

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    Re: 68 Twin Reverb vibrato not working

    Quote Originally Posted by Don View Post
    I've replaced quite a few roaches in recent years. Another thing that I've seen is a failed ceramic disc capacitor in the tremolo circuit. On one customer's '66 Vibrolux Reverb (an almost exact twin of mine), I noticed that the tremolo didn't come on right away- it needed time to "warm up"! One of the three ceramic disc capacitors was shiny with black spots on it. I replaced it and the tremolo was fine.
    That’s very interesting - the vibrato on my ‘’66 Super Reverb doesn’t come on immediately. I will open that amp up in the next day or two and check the ceramic capacitors associated with the vibrato circuit.

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