I have an older Mitsu 55" rear projection set which has seen light use over the years. Recently, the set has been "loosing" convergence. The "red" lens won't hold its convergence position. At times I can "move" it into alignment but it always "jumps" out of alignment. At times I cannot "move" it at all.

(By "move it" I mean in the convergence settings align the red "+" under the white "+")

I have done some reading which suggests I may need the following part:
http://servicemanuals.vstore.ca/index.php/cName/convergence-ics

Here's an excerpt of what I read:
"If the problem is isolated to only one color the replacing those STK amps and any burnt resistors will fix it."

Does anyone here know whether if I replace the STK amp for this lamp if it will solve the problem?

First of all, you don't have lamps. You have CRTs. Much of the advice you get on the web with respect to repairs is often good in a very limited context, and lousy in your own. I suggest you learn a bit about your problem and how these circuits work if you want to be effective. The best place to start is with the first ten posts in the link below:

http://www.hometheatershack.com/forums/diy-repair-maintenance/5600-crt-based-rptv-convergence-repairs.html

I suggest you go to the Mitsubishi specific forums both here and there and post a detailed description of what you are finding along with your MODEL number.

There are also some suggested vendors for service manuals and parts at HTS in the related stickies.

My guess is that you have a bad solder connection and if you repair it quickly you may not need to change any parts. That is just a guess, and without a model, it is hard to relate any specific experience with sets like yours.

Thanks for your feedback. The TV is a Mitsubishi WS-55807.

Symptoms are:
Red convergence is off. Will not move in one direction. Resetting to factory defaults does not cure the problem. This is a persistent issue.

Read the first ten posts in the suggested thread. You likely need to replace the convergence ICs, but you could also have a coolant leak in that model or just need to resolder the ICs.