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Herman-

Sorry for my late reply – your posting got lost in my in-basket for a while.

I needed to upgrade my A-12 two ways:  1) the lamp illuminating the Vernier dial wasn’t bright enough for my tastes, and I wanted red light so it wouldn’t screw up my night vision. 2) The potentiometer on the lamp illuminating the bubble cell was on its last legs, and had to be replaced.

For the Vernier lamp,  I found a red LED that has a screw-in base from a company in China. I cleverly asked for them to send me a couple of free samples… but forgot to ask for the shipping cost. They air rushed them out special delivery assuming that I was a large company and would be placing a large order shortly…   my free bulbs cost $100 in shipping! Unfortunately,  I don’t have a record of who I got them from. In any case there are probably many more sources these days. At the time, red LEDs all required 3 volts, so I had to go with a Lithium C cell battery. At the LEDs (miniscule) current draw, I’m assuming it will last about 90 years.

The bubble lamp was more problematical. I also wanted it to be red, but it had to be variable, and it’s hard to vary an LED’s intensity. (At least I couldn’t figure out how to do it.) So I decided to go with a regular incandescent bulb. The bigger problem was finding a replacement potentiometer. No such luck getting one that would fit in the same size. So I eventually started over from scratch and 3-D printed a whole new lighting assembly:

The cylindrical part fits into the tube where the old one went, and the box-like thing sticks out and contains the on-off switch & potentiometer. The clear plastic light pipe on the front end is covered with a sheets of red cellophane & translucent paper, so it presents a diffuse red background to the bubble cell. This way I can easily distinguish the (red) bubble from the white stars, especially when I turn the intensity way down. Works really well.

So that’s how I did it. There are probably easier (and cheaper) ways to go, but I wasn’t clever enough to think of them.

Paul Dolkas

From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Herman Dekker
Sent: Friday, August 19, 2016 2:44 AM
To: paul@dolkas.net
Subject: [NavList] Re: LED conversion Astra IIIB