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Post subject: Vibrato ticking on my Twin reverb 76
Posted: Tue Dec 09, 2014 7:33 am
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Hello

I am writing from Italy, I hope someone would help me. I have a 1976 Fender twin reverb silver face, i decided to buy a footswitch to control the reverb and vibrato sections, but i have found something strange, when I switch on the vibrato i can hear a clear Ticking. The vibrato works good but it comes with that noise and if u turn the speed control to increase the frequence of vibrato the ticking increase as the speed goes up. What can i do to remove the ticking?

Thanks
Angelo


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Post subject: Re: Vibrato ticking on my Twin reverb 76
Posted: Tue Dec 09, 2014 9:22 am
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The ticking vibrato/tremolo circuit problem is well-known in Silverface era Fender amps. Sounds like you may have an issue with the external foot-switch cable you are using to activate the circuit.

Here's a partial list of fixes:


• Fiberboard contamination: Dust, dirt, and junk can let the LFO signal leak into the audio path. Vacuum the dust and dirt away, and if it still persists, remelt the wax top and bottom with a hair dryer.

• Solder blobs from eyelets touching insulating board: Sometimes excess solder drips out the bottom of an eyelet and can intermittently contact the insulating board, can cause ticking. Remelt the eyelets and examine the board underneath for any blobs dripped down.

• Funny ground on some SF Fenders; On one of the signal tubes, the cathode cap was placed on the tube socket, and wired to a ground lug on the vibrato cancel jack instead of across the resistor on the fiberboard. The vibrato shares this ground line, and can the vibrato current can cause audible ticking in the audio path. Rewire the cap to another ground or relocate it to the board.

• Poor Signal wire layout: signal wires run too close to vibrato leads can pick up the LFO signal. Move them around and see if the ticking goes away.

Bad repair/replacement foot switch cable: the Fender foot switch cable is not two conductor; it's single conductor shielded, plus single conductor. The reverb wire is shielded, vibrato wire is not. This keeps vibrato out of reverb. If you retrofit with two conductor shielded, you get vibrato ticking onto reverb audio.

• Sharp tick in vibrato oscillator: On neon/LDR Fenders, on the neon bulb side of the module there is a 10M to one side of bulb, 100K to the bulb; from the 10M straight across the board is the gnd point of the LDR. Put a 0.02 cap from 10M/bulb to the ground point; this works by filtering the output of the oscillator.


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