About Flashbars

Flashbars are not produced anymore.
If you have a SX-70 camera it is highly recommended to buy an electronic flash for it.

The Flashbar contains on each side five glass bulbs that are filled with magnesium wool in an oxygen-atmosphere.
The magnesium is ignited by an electric pulse.
The glass bulbs are plastic-coated to prevent them from exploding.
The outer plastic wall is another safety-shield and corrects the light-color.
The Flashbar is contacted from the front (active-)side.


The wider contact(H) to the left shorts two contacts in the camera to indicate the presence of a flashbar.
Contacts Nr. 1, 2 and 3 go each to one side of the Bulbs 1, 2 and 3.
Contacts Nr. 4 is the common contact that goes to one side of each bulb.
Contacts Nr. 5 and 6 go each to one side of the Bulbs 5 and 6.
The contacts are spaced 3/32"

Schematic diagram:

There are no electronics in the flashbar.

The camera knows which bulb has been fired by measuring the resistance across the bulb.
A good bulb has a resistance of a couple of ohms whereas a dead one has almost infinite resistance.

Replacing Flashbars with an Electronic Flash

(works also for flash cubes and single-bulb-flashes)

There are several reasons to use an electronic flash instead of the flashbars:

There are electronic flashes (Polatronic, ITT Magicflash etc.) that were designed for the SX-70 which are clamped to the camera and plugged in the flashbar connector.
Note that Polatronic flashes designed for Pronto and 6XX cameras do not fit the SX-70.
A good place to look for one is the rec.photo.marketplace-newsgroup.

If you already have an ordinary electronic flash that you

want to use with your SX-70, you need an interface.

Note that the flash needs to have similar power as the flashbars, which is slightly more than the average photo flash provides.
Flashbars have a fixed light output that reaches to a distance of about 3 meters (10 feet).
The SX-70 exposure control is based on the focused distance.
The camera's maximal aperture (f-stop) is 8.
Your flash should have a guide-number of 75 (9,5 feet * 8)
or a metric Leitzahl of ca. 25 (2.9 meters * 8) at 125 ASA.

The interface

A flashbar-camera generates an electric pulse of ca. 4V , 1.5A to trigger the flashbulb.
An electronic flash has a voltage of ca. 3-12 V between the trigger-contacts (older flashes have up to 300 V !) that are shorted to trigger the flash.

Circuit diagram

How it works:
Three 18 Ohm resistors in parallel (equiv. one 6 Ohm resistor) tell the camera that there is a unused flashbulb in between the contacts 1 and 4.
The firing pulse is scaled down through the resistors and a part of the current lights the LED in the Optocoupler.
The output side of the coupler is darlington array of transistors that can handle 3 to 500V so the same type of adapter can be used with modern and old, high voltage triggered flashes.
Output polarity is important: the center contact of the PC socket must be the positive line.
The line from inner contact to the optocoupler should be insulated with epoxy or something suitable to avoid electric shock if the adapter is used with old (High Voltage) flashes.

flash adapter with shrink tube

Here is a picture of the adapter with my SX-70 and my Metz flash:

Parts list

3 18 Ohm resistor (1W)
1 optocoupler TLP127 (Toshiba)
1 pc socket or a cable with flash-side connector.
The print is single sided on 1mm glass epoxy.

For a DIY project I recommend cutting a dead flashbar open and using its contact strip and its plastic enclosure.

All components are soldered to the front side and it is recommended to cover the circuit with epoxy, especially the output side of the coupler for safety (flash-contacts).

If you would rather buy a complete, tested SX-70 flash-interface look at my flash adapter website

Click here for information about how to modify your SX-70 so it always keeps the aperture open in flash mode (to use the interface with studio flash setups or computer-flashes).