A sound clip is here (MP3 format). It's in three parts. First no tremolo, then fast, then slow. This clip was made using a 1955 Gretsch Country Club, through a 1950s Champ-size Rickenbacker amp, 6-inch speaker. More sound clips soon.

A nice Bo Diddley article from Guitar Buyer magazine, May 2007, is here.

DeAmond's original Tremolo Control (Trem-Trol) units first appeared somewhere between 1946 and 1948. They are purely mechanical devices. The tremolo effect is produced by reducing the volume of the input signal from the guitar (or other instrument) to the amplifier, several times a second. Internally, this is accomplished by grounding the input signal through a water-based electrolytic "hydro-fluid".

The water-based method by which the input signal is grounded, as you would guess, gives the DeArmond tremolo units their unique liquid sound. Here is basically how they work:

• A guitar or other instrument plugs into the tremolo unit, which is plugged into the amplifier.

• Inside the tremolo unit is a liquid filled brass and glass canister, filled halfway with what DeArmond called a "hydro-fluid". The body of the canister is connected to ground. Inside the canister, insulated from the body, is an exposed pin connected to the incoming signal from the guitar.

• A motor shakes the canister. When shaken, the liquid inside the canister splashes against the pin, sending the guitar signal to ground - meaning, the volume is reduced with every splash.

"Hydro-Fluid"

DeArmond's hydro-fluid is a water-based electrolytic fluid, meaning it can conduct the signal coming from the guitar - the fluid is part of the circuit. Although it seems like it would be permanently sealed within the brass canister, the fluid typically dries out over the years. But it can be refilled. (Note: The fluid was NOT MERCURY, as some people assume. In fact, the reason I became curious about the DeArmond tremolo units in the first place, years ago, is by wondering, if it were mercury, where did it go? Every DeArmond canister dries out. Remember liquid mercury from chemistry class? Mercury is too thick to leak. Although it can evaporate, even in the late 1940's the dangers were known and I believe mercury would have been sealed in a glass bulb, as mercury switches are today. And besides, the term used in DeArmond's brochures, "hydro-fluid," obviously implies water.)

The hydro-fluid can be restored using Windex (yes, the blue glass cleaner that has been on the market for decades in the US). After a long search, I received this information secondhand, from someone who had spoken to an ex-DeArmond employee. I do not know if DeArmond originally used Windex brand, or its chemical equivalent. However, Windex conducts the guitar signal perfectly.

NOTE: Don't even think about refilling the canisters in these units with mercury, or replacing the canister with a mercury switch. Mercury is dangerous, isn't correct to the liquid sound of DeArmond units, and mercury will "click" with each oscillation, making it unusable. Mercury would also create an abrupt square-wave tremolo, either completely on or off, and not the smooth water-like tremolo sound of an original DeArmond unit. (I acquired a unit ruined by someone who tried to fix it by replacing the original brass canister with a mercury switch. Now to restore it I need to replicate the original brass and glass canister. Grrrr!!)

Speed control

The other beautiful part of the DeArmond mechanism is the method by which the tremolo speed is controlled.

A motor is used to shake the canister. A tapered pin extends from the motor's shaft. Pressing against that pin, somewhere along the taper, is a rubber-edged wheel. The wheel's hub is slightly off center. When the motor is on, the pin causes the wheel to turn, which causes the wheel's off-center hub to move back and forth. Because the hydro-fluid canister is attached to the wheel's hub, the canister gently rocks back and forth.

DeArmond's speed adjustment control moves the rubber-edged wheel along the tapered pin. Pressed against the far, narrow end of the pin, the wheel rotates more slowly. At the fatter end of the pin, the wheel rotates faster. The motor's speed remains constant.

Subtractive tremolo

The peak volume of the tremolo is virtually the same volume as if the tremolo were not connected. However, with the tremolo on, the volume of the signal is lowered several times a second. The end result is a tremolo unit that reduces the apparent overall volume of the sound. So be prepared to turn up the volume on your guitar or your amplifier when using a DeArmond tremolo.

Restoration

Restoring a non-functioning DeArmond tremolo typically mean refilling the canister. To do this you will need:

• a soldering iron
• de-soldering braid or a de-soldering bulb
• Windex
• a medical syringe (I use a version available at hobby stores)

In the 601, 60A and 60B models (the box-shaped models) the brass canisters are easier to access. The 800 model "foot pedal" unit is a little more difficult, requiring some disassembly to gain access to the canister. With any model, the canister itself does not need to be removed from its position in the assembly. However, on the foot-pedal model, the entire assembly needs to come out to gain access to the canister.

WARNING: Be sure to UNPLUG the unit before any attempt at disassembly. Also, do not attempt to restore this unit unless you are certain you know what you are doing, know how to solder, and take all necessary precautions. The power cord, and the instrument cable, often deteriorate over the decades. Therefore be sure to inspect these cords, and be prepared to replace the power cord if necessary.

I'll describe how to restore a DeArmond tremolo using the older brown, metal box versions as an example (models 601 or 60A). The 60B (molded plastic box) and the 800 foot-pedal models require different methods of disassembly. The internal mechanisms are arranged a bit diferently, but their brass canisters are identical.

To gain access to, and refill the canister, on a model 601 (metal box) unit:

1. Unplug the tremolo unit. Remove the metal cover by removing the four screws holding it in place. Spin the rubber-edged wheel to make sure the springs and linkages are in place and operating correctly.

2. Locate the brass cansiter. Remove the solder covering the canister's fill hole. (The fill hole is opposite from the end that has the braided copper signal wire attached. Or simply, it is the end that faces "up" when the tremolo unit is used.) Access to it is a little tight, so be careful not to let the soldering iron touch or ruin any other parts. Also, be very careful not to let any heated solder drip into the canister.

3. Fill the syringe with Windex, and, watching the markings on the syringe, inject 1.5cc (1.5 milliliters) of Windex into the canister - filling it exactly halfway. When inserting the syringe's needle into the canister, you may need to pierce the rubber gasket immediately within the canister's fill hole. Do this with care. A sewing needle or pushpin may help to gently pierce the gasket before inserting the syringe needle.

Note: If the needle on your syringe isn't long enough to reach the canister, you may need to get creative. If you need to bend the needle on the syringe, slide a guitar string into the needle, bend it, then remove the guitar string. This will allow you to bend the needle without kinking the needle.

4. With 1.5 ml of fluid in the canister, temporarily seal the canister's fill hole. This will allow you to go back in to fine-tune the level of the fluid. This can be done with a small piece of masking tape.

5. Reassemble the tremolo unit, and try it. While it is running, tilt the tremolo unit slightly from side to side. If the tremolo sounds stronger when tilted, you have too little or too much fluid. It should be easy to determine which. Unplug the unit and adjust the fluid level. (You'll notice at this point that the critical advantage of using a syringe is that it allows you to accurately add or remove fluid.)

6. Add or remove some fluid, as needed, and repeat steps 4 and 5. Once the fluid level is allowing the tremolo to sound its strongest, permanently reseal the canister by resoldering the canister hole.

Tip: On several of my DeArmond units, I used a small brass pin or tiny brass screw to help seal the fill hole, then used solder. This makes it easier to reseal, and it's a nice trick to help get back into the canister when that becomes necessary again in the future.

Adjusting the fluid level

After you fill the canister halfway the first time, reassemble and run the unit to test it. You will hear the "fullest" tremolo sound simply by tilting the unit to one side or the other when it is running. This does essentially the same thing as adding or removing fluid. If it sounds better when tilted, you need to add or remove fluid.

You can determine which. Notice that the canister's internal pin is not in the exact center of the canister. If the tremolo sounds stronger tilted towards the pin, you need to add some fluid. If it sounds stronger tilted away the pin, you need to remove some fluid.

The goal, of course, is to adjust the fluid level so that the tremolo sounds it's fullest when it is sitting level.

While you are in there...

Add a drop of oil to the hub of the rubber-edged wheel (it can sometimes bind). Also oil the other linkages and moving parts. Keep oil away from the rubber edge on the wheel and the tapered pin, or just wipe it clean if you accidentally apply oil there. Spray electronic contact cleaner into the potentiometer to prevent scratchy sounds.

Replacing the power cord

As mentioned, the power cords on DeArmond units often crack and can be dangerous. Replacing one is relatively easy. Buy a brown extension cord at the hardware store and cut off the "socket" end. Extension cords are easy to find, inexpensive, color-accurate, and will give you a new cord with a molded 2-prong plug, ready to install. Of course, if power cord replacement is needed, you must do this step first, since you will need to plug it in to test the tremolo after you refill the canister.

Contact me?

This site is in no way affiliated with the DeArmond or Rowe Industries. I have a personal collection of DeArmond tremolo units - it's simply a personal interest. I am not an amp tech, although I sometimes help people, through email, restore their units. Especially, I prevent people from mistakenly messing with liquid mercury, or otherwise ruining these units. It's my contribution to society.

If you have a DeArmond tremolo unit that needs to be restored, and you have questions not answered here, let me know. Depending on my schedule, I may or may not be able to get back to you right away - but give it a try. Also, I sometimes get the urge to add to my collection, so if you have an old DeArmond tremolo unit for sale, let me know.

Dan

Dan Formosa

contact me here

© Dan Formosa 2006

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Dan is a consultant in product design, ergonomics and biomechanics. He has designed a wide range of items for companies worldwide, He started his career by being a member of the product design team for IBM's first personal computer. More recently, working with XM, he developed the interface for satellite radio in the US. His original design and ergonomics work for OXO GoodGrips kitchen tools gained worldwide recognition in design. His work is included in the permanent collection of the Museum of Modern Art in New York.

Aside from DeArmond tremolos, he has a collection of old Gretsch guitars, '60s Vox amps and '50s Rickenbacker M-series amps. On a different note, Dan recently co-authored and illustrated the "Baseball Field Guide," a book clearly explaining and illustrating the complex rules of Major League Baseball.

www.baseballfieldguide.com