Fixed ticking vibrato in 71 Deluxe Reverb using old tube

[Dan Theman]

My Fender DR 71 had an annoying ticking when the vibrato was engaged.
Followed these advice to make it stop:

The official Fender solution (Service Bulletin number 9)
"The ticking caused by the Vibrato is caused by improper lead dress. It can almost be "cured" by connecting a .01 mfd 600 volt mylar capacitor on the 10 meg ohm resistor in the vibrato circuit. this resistor is locatedon the parts panel. Remove capacitor across the 10 meg ohm resistor (old modification) if in place." (That is, run the cap from the junction of the 10 meg resistor and the optoisolator to ground.)

If this does not produce the desired results, then the leads should be dressed as follows and excessive lengths shortened.
1. Dress the leads to the vibrato speed and intensity controls away from the tone controls and filter leads.
2. "Bunch" the leads to the components on the parts panel which connect to
the tube socket of the 7025 (12AX7) vibrato tube."

Adding a cap took away the sharp ticking just a little but still very annoying. Moving around cables didn't make any difference.
Then I replaced the V5 12AX7 with an old (and weak) 12AT7 (A Valvo ECC81) and voilą - the tick is gone! And the vibrato still works fine.
Maybe worth trying fot those who tried the Fender solution above without success.

[Leo_Gnardo]

It's certainly fast and low-tech to try a couple different tubes in the vibrato slot. Sometimes a dog tube there will make other strange noises, not just ticks.

In trying to minimize or eliminate ticks (after trying a couple tubes) addding a 0.01 or 0.02 uF, 600V or 630V, film cap across either A: 10M resistor or B: 10M/Neon junction to ground. Unfortunately in many cases, the tick still remains although muted somewhat.

LED: Replace the neon lamp with hi-brightness 5mm LED. Surprise, it doesn't go up in smoke despite the high voltage at which it's elevated. I've used yellow and orange, and another correspondent mentioned using red with good effect. You can just swap for the neon, or make up a new "bug". I find the photocells in older Fenders often are physically falling apart and not amenable to much poking around, so I keep a couple new photocells handy for cases like this. LED's have a long and short lead, sorry I forget which is anode/cathode, but the long one goes to the 100K, and you're on for a long career of blinks without ticks.

[Dan Theman]

It's certainly fast and low-tech to try a couple different tubes in the vibrato slot. Sometimes a dog tube there will make other strange noises, not just ticks.

In trying to minimize or eliminate ticks (after trying a couple tubes) addding a 0.01 or 0.02 uF, 600V or 630V, film cap across either A: 10M resistor or B: 10M/Neon junction to ground. Unfortunately in many cases, the tick still remains although muted somewhat.

LED: Replace the neon lamp with hi-brightness 5mm LED. Surprise, it doesn't go up in smoke despite the high voltage at which it's elevated. I've used yellow and orange, and another correspondent mentioned using red with good effect. You can just swap for the neon, or make up a new "bug". I find the photocells in older Fenders often are physically falling apart and not amenable to much poking around, so I keep a couple new photocells handy for cases like this. LED's have a long and short lead, sorry I forget which is anode/cathode, but the long one goes to the 100K, and you're on for a long career of blinks without ticks.

Interesting with the LED replacement. So it's as easy as just take out the neon, and solder the LED in its place? What's the thing with the voltage? Can it hurt the amp?

[Leo_Gnardo]

Interesting with the LED replacement. So it's as easy as just take out the neon, and solder the LED in its place? What's the thing with the voltage? Can it hurt the amp?

With a ten million ohm resistor in series, how much current can go there? Not enough to hurt the amp, for sure.

The LED acts similarly to a zener, conducts once you hit a breakover point of 2V or so, and has a nice bent knee as you get there. As compared to the neon, on each cycle the voltage across it rises to about 90V then suddenly breaks down as the gas ionizes and flashes - snaps down to about 60V. It's the sharpness of the Ne breakdown to flash that shows up as a pop in the audio. With the LED, there's less than 1/10 the voltage involved, and no sharp current spikes as the LED flashes.

How long do it last? So far I've been using this technique, about 5 years, nobody's brought back a malfunctioning LED-modified vibrato. So far so good.

[Jazz P Bass]

LED's have a long and short lead, sorry I forget which is anode/cathode, but the long one goes to the 100K, and you're on for a long career of blinks without ticks.

FYI: The 'long lead' of an LED is the Anode (positive) terminal.

[Dan Theman]

And you just snip the neon and put the LED there instead? Nothing more?

[Leo_Gnardo]

And you just snip the neon and put the LED there instead? Nothing more?

One of those rare things where "it's that simple." With a superbright LED you can get away with less than optimum aim at the photocell. If you're making your own "bug" easy enough to line up the cell & LED within a length of black heat shrink tube. Flick your Bic and bingo, you're a bug maker.

[drewl]

Right, and if leads were previously cut, inside the LED the larger mass of metal is negative.

I used a photocell from my son's circuit set with an LED to make a "bug" once.

[Drewline]

I've used the info in service bulletin #9 any number of times with good results in the past. Next time I'm giong to try the LED mod Leo suggested.