Hi, I have a viceroy d300 viewer that I have been using until the bulb went. I bought some 6v 10w bulbs from Amazon and fitted one okay. But then wanted to adjust it to see if I could get a brighter screen and since then the tightening screw will not hold it in place. I have tried refitting the blown bulb which stays in a place a bit better but still slips out a bit. Any thoughts? I am really baffled as I can't see any obvious issues with the tightening screw mechanism (other than the screw head is not so great but it still screws tight...(are these tiny screws replaceable?). Thanks in advance for any advice. Clare