The long thin 28 volt incandescent bulbs that are used to light up the Ampex VU meters in the AG-440 series as well as the MM-1000 units are long discontinued. There are smaller bi-pin bulbs available from suppliers such as www.jkllamps.com, but the 2 pins that stick out of the bottom of the bulbs are too thin for the sockets to grab, so you’d have nothing but intermittent connection problems with them if you tried. Also, the current bulbs are a lot shorter, so they won’t quite fit into the VU meters regardless.
Fortunately, there’s a long term quick fix for this.. change the incandescent bulbs to LED. While the color won’t be the same, the meters at least will be lit up perfectly, and the LEDs should outlast the life of the deck.
Materials required:
- Philips screwdriver
- 1/8” heat shrink tubing
- Soldering iron and solder
- Wire cutters
- 2- Dialight warm white LEDs per electronics channel
- 1- 4.7K ohm ¼ watt resistor per electronics channel.
There are many sources for the 8mm panel mount w/wires attached LEDs, including eBay and Alibaba, but we bought ours from Mouser. The Dialight part number is:
According to the manufacturer, these are ‘warm white’ LEDs.
The voltage that supplies the 28 volt incandescent bulbs is 39 volts, so the two 28 volt bulbs are supposed to last a long time. Of course due to age, and the machines being moved around, the filaments get brittle over time, and thus the bulbs burn out.
Installing new LEDs to replace the incandescent bulbs is about as easy as it gets.
Remove the bottom cover of the electronics section
There are three Philips screws that hold the bottom metal shield cover onto the AG-440 electronics. Only the screw in the middle of the bottom cover needs to be taken out completely. The two screws at the back just need to be loosened a turn, and the bottom cover will lift out and off of the chassis.
Remove the old Incandescent lights from the electronics section
Each bulb is held in place with a small clip that is attached to the VU meter housing. Pull the bulbs and the socket out on each side of the meter.
1. Cut or unsolder the red wire from the bulb socket on the right (or left bulb, depending on which version of 440 electronics you have.
2. Clip the new LEDs in place into the existing holders (they snap right in), and push the bulbs forward into the meter housing. (note that you can partially control the brightness of the meter face by how far into the meter you push the bulbs).
3. Cut the red and black wires of each LED down to about 5” from the 14” that they come with.
4. Slide a 2-3” piece of heat shrink tubing over the black lead of the left LED.
5. Cut the leads short on a 4.7K ohm resistor, and solder one end to the black lead of the left LED. Solder the other end of the resistor to the red lead of the right bulb. The two LEDs are now in series with each other.
6. Slide the heat shrink tubing over the resistor and solder connections, and shrink into place with a lighter or a heat gun.
7. Slide a piece of 2” heat shrink over the red wire of the left LED, and then solder that red wire to the red wire that was unsoldered from the old bulb socket.
8. Follow the other wire from the right incandescent socket down to the terminal strip on the right of the VU meter. It is the second pin from the top, which is a ground pin, and that connection completes the bulb/LED circuit. You can cut this lead, strip it, and put heat shrink over the black wire of the right side LED, and solder it to this ground wire, or do as we did, cut the existing wire short right at that ground terminal, and solder the black wire of the right LED to that ground terminal.
Reassemble the bottom cover on the electronics channel, reinstall and test your handiwork.