The TU-83: A Ruggedized Caving Strobe

by John Ganter

The Vivitar 283 has long been popular among cavers. It is relatively cheap ($70), not too large, and powerful. Unfortunately, the 283 (like most strobes except large, expensive divers strobes) is not designed to resist extreme cave conditions. With care, it will function remarkably well, but liquid mud and water conditions will cause it to short out and/or the switches will jam.

Here I describe a re-packaged 283, which is housed in a piece of PVC pipe and dubbed the "TU-83." At the cost of a weight gain of 59% (15.75 to 26.5 ounces) and a volume gain of 61% (about 26 in3 to 42 in3), the TU-83 is very resistant to mud and water.

First I will describe the insides of a 283, then explain how I moved some of them into the new housing. The project can be carried out with home workshop tools and off-the-shelf materials. You will need hand tools, soldering capability, a drill and a small saw (a coping saw is perfect). The cost is around $10.

Note that you will certainly void the warranty on your 283, and you could ruin it. Also, there are significant electrical hazards to the person doing the modification and to operators of the strobe. These will be discussed more below. This article is written to provide ideas to experienced and knowledgeable electronics hobbyists, and the author will not be liable for any consequences that occur.

How Xenon Strobes Work

A brief overview of how strobes work may help the prospective 're-packager' to understand the design decisions that I made, and modify these for their own needs.

Xenon gas releases an intense white light when high-voltage passes through it. This voltage is created from the 6 VDC (volts direct current) available from batteries in a typical strobe as follows. The current is run through a thyristor or integrated circuit that switches it on and off very rapidly, producing a wave or 'signal.' The current is now AC (alternating current). Unlike the 60 Hertz (60 cycles per second) in house current, this wave is extremely high frequency, typically over 10,000 Hz. This results in the rising whine that is heard from strobes.

The AC, still at 6 volts, is fed into the primary windings (loops of wire) of a transformer (called the 'oscillation transformer'). The current, because it is alternating, sets up a moving magnetic field in the transformer. Nearby are the secondary windings. These respond to the magnetic field by producing their own current. If there were just a many secondary windings as primary, the voltage would be the same.

But if there are, say, 60 windings in the secondary for each in the primary, something rather amazing happens. Six volts goes in the primary and 360 volts comes out the secondary. Suddenly there is high voltage.

This energy is stored in a capacitor which is in turn connected to two electrodes -- one at each end of the flash tube. The capacitor stores up enormous energy, and nothing happens. The Xenon just sits there.

It sits there until another transformer, the trigger coil, zaps the tube with an even higher voltage when the photographer fires the flash. Suddenly the Xenon ionizes and all the electricity in the capacitor pours into it and produces a brilliant flash.

The Vivitar 283

The 283 has an articulated head that swivels from straight-ahead to vertical when mounted on a camera hotshoe (Figure 1). Below the head is a sensor that provides 'auto exposure' capability; it shuts down the flash and recycles the excess energy when sufficient light is computed to have reflected from the target. A filter may be rotated in front of this sensor to reduce power to 1/2, 1/4, 1/8 and 1/16. (Apparently the auto exposure module is an optional accessory on the 283; I bought mine used and it was included.) A scale on the side of the unit (which may be illuminated by pushing a button) shows the ranges and f-stops for these settings. On the back of the 283 are a power switch and a combination ready-light/fire switch. There is also a small light that glows briefly to indicate that the auto circuit has judged there to be sufficient light. On the side are a 330 VDC input for running the unit off a house-current adapter, a PC connector and the cover of the 4 AA cell battery compartment.

Fig01_072.gif (10471 bytes) Figure 1: Schematic of Vivitar 283 showing approximate shapes and locations of components

Inside the 283 there is very little wasted space. Sitting in the bottom is what I call Board 1; this contains the power supply (the thyristor or IC and the main transformer) and much of the 'user interface.' Squeezed in between the battery compartment and the case is what I call Board 2; this contains much of the auto-exposure circuitry.

Within the 'knuckle' of the articulation is the large capacitor that is the 283's best component. For its capacity, the capacitor is actually quite small: 1100 microfarads at 350 volts. It must be treated with care. There is also a small switch that activates the Bounce Control Circuit (BCC) when the flash is tilted up.

In the articulation is Board 3: this contains the trigger coil and other components, and connects to the reflector and straight Xenon tube at the end.

The 283 has evolved over about 25 years. Information on versions is available in the service manual supplements (see information on sources).

Since I want raw power, I decided to abandon the auto-exposure feature, with savings in weight and bulk. It would be possible to retain this feature by putting it in another little window where it could see the subject but not the flashtube. Changing the setting while retaining water resistance would not be easy, however.


The manufacture forbids disassembly because this exposes hazards. It is important to understand these hazards before proceeding:


If shorted, the main 283 capacitor will produce a violent arc and/or serious shock. It should be be handled with caution. Before opening the case, the power should be switched off and the flash discharged completely. Immediately upon opening the 283, both the main capacitor and the largest one on Board C should be discharged through a 10 ohm, 10 watt power resistor for about 30 seconds. It is a good idea to leave it shorted out completely while the case is open, since it can 'bounce back' to annoying if less spectacular voltages.


In wet environments, any strobe presents a serious shock hazard to the user. There is also some hazard from exploding hydrogen gas that may evolve from the batteries. Since the user is likely to be a photo assistant who has no knowledge of the strobe's hazards, it is the responsibility of the strobe builder and owner to

  • protect the strobe internals from water which could result from housing leakage, operator misuse or accident
  • protect the operator from the strobe through insulation and ruggedness

This protection is primarily through design, construction, maintenance, and testing of the strobe enclosure. These tasks are the responsibility of the strobe builder and owner.

The 283 can be opened by removing about 6 screws and gently prying apart the case.

Once the capacitors have been safely discharged and sedated, work can begin. Treat the parts with care, especially the wires that connect boards, because if you cause damage it may be difficult to locate the problem. Take careful notes on connections so that if you cut the wrong things you can repair the damage.

The steps that I followed are roughly as follows:

1) Desolder the small board that sticks up from Board 1. This contains the PC and 330VDC input sockets.

2) Cut the wires that lead to the BCC switch.

3) Cut all the wires that lead to the auto sensor and socket.

To fire the TU-83, you solder wires across the 'Test Fire' button contacts. For power, you glue the switch 'On' and insert a switch in the wires from your new battery holder. You also relocate the 'Ready' lamp by desoldering it and moving it elsewhere. More about all this later.

The Tube and Reflector

In testing I noticed that the 283 reflector is not opaque; a fair amount of light leaks out the back. I want this light out in the cave, so I carefully insulated the electrode connections on the tube with GOOP adhesive. (It is probably important to leave the tube somewhat loose so it can expand and contract.) Then I covered the back of the reflector with aluminum foil, again stuck in place with GOOP.

The Window

The main challenge of a cave strobe is getting the light out into the cave while keeping cavernous substances (mud, rock and water) at bay. I cut a rectangular hole measuring 2 5/16 by 1 1/8-inches (the size of the strobe reflector) in the end of the PVC housing. I did this by drilling a hole at each corner, then re-assembling a coping saw through one of the holes and cutting out the rectangle.

Over this opening I placed a piece of 1/4-inch thick glass measuring about 2 1/4-inch by 3-inches (Figure 2). The seal was created using Ultra Blue silicone, a tough gasket silicone. I then retained all of this with two brackets made from aluminum angle and counter-sunk brass screws running into the housing. The ends of the screws were sealed with silicone, and the reflector fixed into place with a couple of wire-ties.

Fig02_072.gif (9860 bytes) Figure 2: Cross section of the flash window. The flashtube and reflector assembly is held against the glass window with wire-ties.

I got the glass, which is commonly known as 'double-strength,' at a hardware that had a perfect 3-inch wide scrap sitting around. The other dimension is a little bit wide; 2-inches would probably do it. But if it is too narrow, there is not enough room for the retaining brackets to grip the glass while still not blocking the light. Lexan polycarbonate could also be used. It would be lighter and tougher, but unfortunately it is also much less scratch-resistant than glass.

The aluminum angle is very small: about 3/8 by 7/16-inches. I could not find any this size, and had to create it by sawing up a more complex shape that I scavenged from a junked computer.

The Housing

The housing is a 'clamshell' created from 2 end caps and a piece of 4-inch PVC drainpipe. To save weight, the caps and pipe should be the lightweight 'Sewer and Drain' variety, not the 'Schedule 40' heavy-duty stuff. The caps are simply slipped on the pipe and butted up against each other, then sealed with several wraps of duct tape. A heavy-duty version of the TU-83 would use an O-ring between the caps, and they would be locked together with the stainless steel clamps used on diving equipment.

As construction of the housing proceeds, it is important to test repeatedly for water-resistance. This will help reduce the hazards mentioned above. Place the housing in a bucket of water and look for bubbles.

Arrangement of Pieces

Having disassembled the 283, you now have a tangled mass consisting of three boards, a capacitor, the tube/reflector assembly, and a 4 AA cell holder to replace the battery compartment. Basically I just made a triple-decker sandwich out of the boards (Figure 3), with some foam sheeting between them to keep things from shorting out. I then stuffed this sandwich, the capacitor, and the battery holder into a block of 3-inch thick foam that I had carved into a circle and gouged some holes through.

Fig03_072.gif (16810 bytes) Figure 3: Schematic of TU-83 showing approximate shapes and locations of components. The components in the top part of the figure are embedded in a block of foam.

Nothing is very critical here, except that the thyristor should have some ventilation space and the leads on the battery holder should be long enough to allow it to be pulled out for battery replacement.

Hydrogen gas management

When alkaline cells are discharged, they can produce small but dangerous quantities of hydrogen gas. Normally this gas dissipates, but in a sealed device it can build up and be triggered by a spark, causing an explosion. (See In the 1980s, there were reports in the British caving literature of point-and-shoot cameras exploding, so it can happen.

The usual approach to hydrogen in dive lights, dive scooters, etc. is a platinum catalyst. This catalyst converts hydrogen into water. With some difficulty, I obtained a small quantity of platinum catalyst beads. I do not know of an easy source, but divers who build custom equipment may know of them.

I made a small bag from stocking material and filled it with a mixture of catalyst pellets and silica gel (to absorb any water).

Trigger connection

Cavers routinely have trouble with PC cords; they are so tiny that even in clean caves they can get plugged up. I have abandoned them. Instead I use 'de-rated' 120 VAC household connectors. Since these connectors are designed (rated) for such high voltage, they are made of heavy-duty brass which is ideal for caves. They resist water and mud, and they don't corrode if treated reasonably well. They are larger than I would like, but I am willing to pay this price for reliability and low maintenance.

For a flash connector I use a 'grounding adapter,' one of those things that you use at home to convert 3 bladed plugs to 2 bladed receptacles. Be sure to use the one-piece molded variety, not the ones assembled out of pieces. Take a knife and cut off the third hole (the ground). This is my rugged, waterproof version of a female PC connector.  On my Nikonos cameras I have about 3 feet of the male end of an ordinary extension cord. This serves as the male PC cord. I then tightly wrap several turns of electrical tape around the connection if wetness is expected.

Polarity is important if you are going to use certain slaves. Household plugs and receptacles are polarized. I have decided that the wider of the two plug spades is always negative, since it looks the most like a minus sign.

For manual firing, I use a little molded plug (off a household extension cord) with a pushbutton switch glued onto it. The advantage of this is that the switch is external; it doesn't let water into the housing. Also, it can be thrown away without having to work on the housing if it jams up from mud.

The Control Panel

The control panel is the rear cap of the housing. On one side of the control panel is the firing connector discussed above, glued tightly into a square hole with GOOP. On the other side is the power switch.

This switch caused some problems; I wanted it to be very rugged, waterproof and immune to accidentally turning on. My solution was to modify the strategy used for the PC connector. I just shorted out a Quick-Install plug (the things you clamp on lamp cords without stripping the wire) and put it on a short tether. Plug it in; the power is on. Pull it out; the power is off.

Beside the power switch is a little jewel window. Behind this is the 'Ready' light, glued into place and with an aluminum foil reflector.

The six wires for these controls are wire-tied together into a bundle that runs from the rear cap to the boards in the foam.

Photo_01.jpg (43168 bytes) TU-83 opened to show the main components embedded in foam (left) and the end cap (right) with sockets for power-on and trigger
Photo_02.jpg (30445 bytes) TU-83 back panel showing power-on switch (left) and trigger (right). The 'short out' power switch/plug was later replaced by a rubber membrane that allows the user to operate an internal pushbutton switch.
Photo_03.jpg (33639 bytes) The completed TU-83 shown beside the empty 283 housing. Normally the TU-83 would be tightly wrapped with duct tape at its center, where the two caps meet.

Weight and Volume Analysis

As mentioned, the original 283 makes very efficient use of space. I estimate its volume at around 26 in3. The various components take up about 22 in3, so it is roughly 85% space efficient.

The best that I could do was about 52% space efficiency; with the housing caps butted the volume of the TU-83 is 42 in3. There is a lot of wasted space there, but it would be difficult to do better without messing around with the boards.

In terms of weight, you lose some and gain some (Table 1). The TU-83 is heavier than I would like, but bearable.

Part Weight in Vivitar 283 (ounces) Weight in TU-83 (ounces)
Boards, reflector, tube, capacitor 5.75 5.75
Exposure dial, front lens, hotshoe 1.0 removed
Sensor, socket and board 0.75 removed
Battery holder 0.5 0.5
Power switch assembly   1.0
PC connector   0.75
4 AA alkaline batteries 3.25 3.25
Housing and window 4.5 11.75
Total 15.75 oz (1 pound) 26.5 oz (1.6 pounds)

Use and evolution

I have used the TU-83 to trigger slaves on flashbulbs, and as a short-range or fill flash.

It could also be used as a main flash for a point-and-shoot (PAS) camera. Here it has the advantage of syncing with the PAS, which flashbulbs will not do because they burn too slowly. (Flashbulb synchronization appears to be possible if the camera has 'Slow sync.') But because one cannot control the aperture on a PAS, you have to control either the flash power or the flash-to-subject distance. So the power control which I eliminated from the TU-83 would actually be very useful with a PAS camera.

One problem which I encountered is color temperature. The 283 flashtube light is very blue. That is why it has a gold filter over it. I ended up gluing this filter on the front of the window. This makes it vulnerable to mud, so it would be better to place it behind the glass.

Using the plug for the power switch was not as quick and easy as I had hoped. I have found that there is a lot of workload when setting up a cave photo, so using both hands to hold the strobe and insert the plug takes too much time and effort. I talked to Bill Farr about the re-packaged strobes he has built. He used a piece of inner tube rubber as a membrane through which he can operate normal pushbutton switches. I ended up retrofitting the TU-83 with this feature (sorry, no photos), and it has worked very well.


The TU-83 was the first strobe repackaging project I tried. The choice of PVC pipe led to a fair amount of wasted space, so the TU-83 is bulky. I have found that it falls into a position where it is not used much in my photography. If I go light, I take a PAS camera loaded with ISO400 film, and a couple of tiny Wien slave-strobes. The TU-83 is too bulky and heavy when I am in this mode.

If I go heavy, I take my Nikonos 3 and a small trigger strobe sealed in a BUD box (to be discussed in a later article). The main flashes are slaved bulb guns. In this case the TU-83 is so much weaker than the bulbs that I tend not to carry it. However, it might be useful as a weaker fill flash, for example to illuminate the model's face when they are strongly backlit by a bulb.

I might try packaging a 283 in a rectangular, O-ring sealed BUD box for more power in PAS use. But I would want the variable power setting, and that would be problematic. In the long run, considering the time and effort required, an Ikelite Substrobe 50 at $350 might be more economical (  Interestingly enough, it weighs 1.3 pounds and does not offer control over power level.

Parts List

- aluminum angle: about 8 inches
- battery holder for 4 AA batteries
- (4) brass screws, nuts and lock washers: about 6-32 x 1-inch
- PVC pipe: thin-wall drain pipe, not Schedule 40 (hardware or home center)
- caps: for 4-inch PVC pipe, light-weight (hardware or home center)
- foam: thick and thin
- glass: double-strength (full-service hardware)
- grounding adapter
- jewel window (from small panel lamp)
- hydrogen catalyst (unknown: after-market battery supplies, diving equipment?)
- silica gel pack (appliance packaging)
- UltraBlue silicone: from Permatex (auto supply)
- GOOP (hardware or home center) Note that all standard varieties of GOOP are identical; they are just marketed for different uses like plumbing, automotive, etc.


Don's Xenon Flash and Strobe Page.

Edgerton, Harold E. 1987. Electronic Flash, Strobe. 3rd Edition. Cambridge, MA: MIT Press.

Siemens Components Group. undated. Everything You Always Wanted to Know About Flashtubes. 6 pgs. Free.

Vivitar. 1976-1979. Vivitar Service Manual for the Model 283, with 3 supplements. About 50 pages. Vivitar no longer sells this manual to the public. But it may be available from or other sources.

Version 1, 15 February 2000.


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