Hi Wcrowe and welcome to the forum!
Lt-3K will be the model of the kiln sitter on the kiln, not of the kiln itself. Manuals for Duncan kilns about 1/3 the way down this from Paragon, it should have the height info in the manual. The kiln will have a faceplate on it with the kiln model number etc, you can see the model numbers in the link.
nataniajoy, you are very fortunate to have such a nice manual kiln as a gift. i thought by now you would have received an answer that addresses your problem as a totally new kiln user.
couple of things might help you understand the manual fred has so helpfully found for you. you need to realize that the kiln is a very old one as far as its manufacturing date is concerned and there was a slightly different vocabulary used then. "Automatic" back then meant your kiln was equipped with a Kiln Sitter that would mechanically turn off the kiln when a particular temperature was reached. the manual keeps referring to it as the ASD, automatic shutoff device (or sitter. prior to the use of a sitter, the potter had to watch the firing and turn it off at the end by looking into the kiln peep holes and judging the temperature at which to turn off the electricity. ) cones have been use for over a hundred years to help do that.
the temperature you select for each firing is commonly referred to by a cone number. that means the same kiln can be used by potters who fire earthenware or stoneware which is usually fired to a higher temperature. so you need to select the cone number for the clay and/or glazes you are using.
the number on the cone indicates a temperature but the firing can take a little longer as the elements wear out over time. so the cone ,which you place HORIZONTALLY across the two little arms, will determine the time and temperature of your firing. the arms hold up the cone and the rod end of the "claw" of the sitter sits over the cone resting on it. SINCE THE INVENTION OF CONE BARS MANY PEOPLE USE THEM IN THE SITTER. bars are of a uniform size end to end. cones are tapered and some people have trouble putting them onto the arms and getting the claw rod in the middle of the cone.
when the cone gets hot enough for a long enough time, it will melt. that means it sinks down and allows the rod end of the claw to sink as well. the other end of the claw, the part outside the kiln, is really the claw looking end and it is holding a weight that will be released by the rising of the claw. the weight will snap down and activate a round electrical shut off button that is located on the outside of the sitter. (if you find you cannot start your kiln at any time, check that the claw is holding the weight and the button is close to the kiln, not sticking out.)
i hope this is enough to help you read the manual and that will explain your particular kiln.
the most important thing you need to learn is that it is CRITICALLY IMPORTANT that you understand the cone numbers of your clay and glazes. look at a CONE CHART and read the numbers and the temperatures carefully. there are some essential facts that are commonly glossed over when experienced potters are talking to each other.
09 08 07 06 05 04 03 02 01 AND THEN CONE 1 2 3 4 5 6 7 8 9 10 ETC. are each a little hotter running from left to right. check the chart! and check your clay. write the cone # on the bag of clay so you DO NOT make the mistake of thinking that cone 6 is the same as cone 06. that is a completely different temperature and if you use cone 06 clay and use a #6 cone in your sitter, you will probably melt everything and ruin the kiln.
see the recent post by benzine for what can happen.
hope you bothered to read this long post and understand it.
