If you don't have anything to regulate the UTH I would get something ASAP. It is very likely that your temps directly on the glass above the UTH are getting above 90. I tested an unregulated zoo med UTH once (without a snake in the tank) and the temperature reached over 110 degrees before I unplugged it.
An actual thermostat is the preferred way to go. The "herpstat" proportional ones are always recommended
http://www.spyderrobotics.com/products/herpstat.html The Ranco stats are also fairly popular, though it is an on/off stat, not a proportional.
http://www.reptilebasics.com/ranco-e...pre-wired.html
If you don't have the money right now for a thermostat you can look into a rheostat. For this you can pick up a lamp dimmer switch from Home Depot or most other hardware stores.
http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053 With this you have to play with the switch, raising and lowering the switch (and therefore the power to the heat pad) until you get to the preferred temperature reading on the thermometer. If the temperatures in your house go up or down a lot (say from winter to summer, etc..) then you have to keep a close eye on that thermometer because the heater will raise and lower temps with the change in house temperature, and you have to adjust the dimmer switch accordingly.