PX13 mercury batteries, which were commonly used in the 1960s, 70s, and 80s to power camera and camcorder lightmeters due to their voltage stability, have long been banned from sale for environmental reasons.

This simple modification allows you to do without them and continue using these excellent Super 8 cameras.

Using a voltage regulator, the 9V from the four R6 batteries is converted to 3.3V, then a simple diode reduces the voltage to 2.7V, which is the theoretical voltage of the two PX13 batteries in series (2×1.35V).

You will need:

Start by turning off the camera by folding down the handle and opening it by removing the front cover after unscrewing the four screws.

You will then have access to the main board.

Using a multimeter set to the position that beeps on contact, place one probe on the 0V mark on the blue wire at the bottom of the board and find the 0V mark in the center of the board with the other probe.

Replace the handle and turn on the camera by sliding the power switch (with the white line) to the right.

Set the multimeter to DC voltage (=), place the – probe of the multimeter on the 0V on the blue wire at the bottom of the board, and find the 9V from the batteries in the center of the board with the + probe.

Turn off the camera and remove the PX13 batteries if there are any in the small compartment under the camera. Cut the yellow wire at the bottom of the board that connects the + of the two PX13 batteries to the point marked 2.7V. You can leave the wire in place by insulating it properly, in case you want to go back.

Then solder the L78L33 voltage regulator in a TO92 package, respecting the following pinout:

That is, pin 3 on +9V, pin 2 on 0V, and leave pin 1 output open for now. Being careful, you can now turn the camera back on and check with the multimeter that you have +3.3V on pin 1.

Turn the camera off again and solder a 1N4148 diode to the regulator output, ensuring it is the correct way round.

Use the multimeter in the position that beeps on contact to find the correct track connected to the +2.7V point where the yellow wire was connected. Insulate the diode with heat-shrink tubing and solder its cathode to this track. Use the multimeter in DC voltage measurement mode to check that there is +2.7V at the point marked 2.7V with the camera turned on.

Be careful not to accidentally connect two tracks when soldering! You can also cover your assembly with insulation to ensure that no contact touches the cover.

That’s it. Replace the camera cover and check that the lightmeter is working properly.

Many thanks to André Egido, who used to make this modification for his customers at cine-super8.net.