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Post subject: Another Tremolo Ticking fix for DRRI
Posted: Tue Jun 07, 2016 7:26 pm
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A while back, I repaired the CDS cell on an old bug. The lead had been twisted and broke loose.
The stock connection is just the lead mechanically smashed against the substrate. I epoxied the backside for mechanical strength. I used a CircuitWorks conductive pen with it's silver-loaded glue. Then the silver glue gives a low resistance connection.
I recently tried the same method on a DRRI with a bad tick in the Tremolo..
I cut open the bug laterally and lifted the CDS cell up.
The cell is sealed under a layer of plastic, so it needs to be exposed..
Supporting it with a bit of Styro popcorn, I scraped the ends of the leads. Then I carefully scraped around the leads until I saw a little bit of shiny metal. I don't think its critical if you scrape it through a bit.
The CircuitWorks pen has a spring loaded tip for dispensing that is difficult to use in a small space like this.
I unscrew the pen, which has left-hand threads. Then using a toothpick or needle, dab a small amount around the leads. Work quickly as it dries fast. Store the pen in your freezer to keep it from drying up.
Reassemble the bug and seal it with black silicone around the H.S.tubing
The ticking went away except at 0 on the speed control. The noise also seemed lower. I know I can just buy a new bug, but I feel this is probably better than new.

The CircuitWorks pen is also good for improving the crimped connections on pots.and any other low power connection that can't be soldered.


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Post subject: Re: Another Tremolo Ticking fix for DRRI
Posted: Wed Jun 08, 2016 1:01 am
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Location: Province de Québec, Canada
Great work,

I built some spair optocoupler for Fender amps. Same as original. Parts cost me $2.25 from my electronic store.


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Post subject: Re: Another Tremolo Ticking fix for DRRI
Posted: Wed Jun 08, 2016 9:44 am
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I haven't been able to find an accurate match to the stock CDS cell. What do you use?


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Post subject: Re: Another Tremolo Ticking fix for DRRI
Posted: Wed Jun 08, 2016 10:22 am
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Joined: Fri Feb 05, 2010 4:31 am
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Location: Province de Québec, Canada
A standard neon lamp NE-2;

http://www.jameco.com/webapp/wcs/stores ... 1_27351_-1

Photo resistor

https://abra-electronics.com/educationa ... o-300.html

Plus a piece of heat shrink tubing

My store is Abra Electronics, close to my home.
Many photo- resistor with different resistor value work.
I put these parts in some Blackface amps. Work like the original.


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Post subject: Re: Another Tremolo Ticking fix for DRRI
Posted: Wed Jun 08, 2016 3:47 pm
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Yes, another informative tech post. Thanks Tim. I had to look up whats a CDS cell. And keep the pen in the fridge. Interesting. Great fix.
Not that I know anything about this,
A Neon bulb works, isn't the turn-on voltage too high?
What was Leos original part for this? Whats used today.

Why does the Vibrato signal have to be optically isolated anyway?
Can't the signal just be coupled to its circuit destination.


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Post subject: Re: Another Tremolo Ticking fix for DRRI
Posted: Thu Jun 09, 2016 6:33 pm
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Well, if I can't find an exact replacement for a part, I like to refurb the original, if I can.
In this case, the CDS cell has many variations in on/off resistance.
I checked out the web sites for the manufacturers and there are many models with slight differences.
I'm sure there is an engineer and a buyer at Fender who have lost sleep over the choices.
Rather than second-guess these guys, I'll just improve the old one.

The Tremolo bug consists of two parts; a neon bulb and a light sensitive resistor called a CDS cell. It is made from cadmium sulfide, a banned substance in some parts of the world.
The Neon bulb is pulsed by the tremolo oscillator tube at 90 volts. The control signal in the CDS cell is less than a volt AC.
The bug optically couples the flashing light from the neon bulb to the CDS cell to vary the small audio signal for the Tremolo effect.

There are mods to reduce the tick that add capacitors to smooth the voltage to the neon bulb that kinda work.
I'm trying to go after the source of the tick.
I have a hunch that this mechanical connection is where the tick is generated. Lowering the resistance of the connection reduced the tick. Nothing but bug replacement has worked as well for me, so I'm gonna try it on more of them to see how they work out.


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