I recently was asked to repair a Dyna Spot that was owned by a school from new - getting hot and the light output was low. The spot had recently had a 1500W DTA lamp installed - listed as the alternative to the DTJ 1500W incandescant lamp in the Altman literature. they wanted to save lamp cost by using the 100 hr halogen lamp. When I removed the cover and inspected the unit I was surprised to notice that the filament position was too low - by 3/4 of an inch. The top of the filament support frame is actually on the optical axis. I checked the lamp holder mounting and it has not been changed. I swapped in a DTJ lamp and the filamment centre is correctly located on the optical axis. I checked the specs for the lamps and they should indeed be a direct fit for either type. The only clue I found was a picture of an Osram lamp on the internet that suggests that the Osram DTA may be a longer lamp. So possible explanations include: the Ushio lamp in this fixture is not really a DTA lamp; or there has been a design change in the DTA lamp that is not reflected into the lamp specs; or (which seems unlikely) the DTA lamp was incorrectly specified for this fixture due to a lamp spec error; or there is some other explanation that someone else is aware of. Any ideas or suggestions. I can easily fix this by making and installing a spacer under the Mogul Prefocus lampholder. Of course this explains why this follow spot was getting hot and not producing much light output.