trem help in AB763 twin reverb

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by brad347, Mar 20, 2006.


  1. brad347

    brad347 Member

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    Fired up the old twin today (hadn't played it in a few months) and the tremolo is very weak... I never use the trem much so I don't know how long it's been like this. I can hear the faint "tick tick" when the trem is on and it speeds up when I adjust the speed control and everything... but it's not actually tremoloing the signal. When I turn the intensity control all the way up it's just barely audible but you really have to listen for it. I tried another tube. Footswitch is good and switches off the ticking. I also cleaned the footswitch jack. Any ideas?
     
  2. doctorx

    doctorx Member

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  3. John Phillips

    John Phillips Member

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    If you can hear it ticking both the tube and the neon are OK (the ticking is the discharge from the neon leaking into the audio path), so that just leaves the LDR - both the neon and the LDR are inside the 'roach' made of heatshrink tubing. You'll need to replace the whole thing unless you can find the correct LDR. Fender sell the complete roaches as spares so it isn't a problem.

    I've noticed a lot of these failing in older Fender amps recently - it's almost always the LDR part that goes. They seem to have a life expectancy - maybe around 30-40 years, although they certainly don't all fail even after that. I didn't come across any dead ones at all until about ten years ago, then maybe one or less a year, but now at least five in the last couple of years. On the other hand a lot of people never use the tremolo at all, so maybe they wouldn't notice it was dead ;).
     
  4. brad347

    brad347 Member

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    That's what I figured. Bummer because the amp is for sale and a guy is coming by to look at it tonight :(
     
  5. mbratch

    mbratch Member

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    What causes the pulse to leak into the audio path and how do you fix it? My trem works, but I get the ticking whenever it's on, regardless of intensity setting.
     
  6. brad347

    brad347 Member

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    i've heard that you can substitute a large frosted LED for the neon bulb but I haven't tried it. I think otherwise the pulse will leak into the audio path a little. I've also heard that using a weak 12AX7 for that slot can help reduce the ticking.
     
  7. doctorx

    doctorx Member

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  8. brad347

    brad347 Member

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    replaced the roach with a repro from Hoffman today, works like a champ. Thanks for your help.
     

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