I too lucked out and got a good one on eBay, several others I bought I was not so lucky.  It's my daily driver.  I did adjust the timings on it, a little touchy but doable.  If you get the service manual it will tell you the proper temps and timing to switch from high to low.

Occasionally I will cut up a paper filter and place it on the bottom of the strainer basket, not sure if it really adds to the flavor, but I generally think so.  The original units had a cloth filter, so I thought why not try paper.  I also have mine set up on a timer, so I have fresh coffee in the AM when I get up.

Hope yours works well.

I have an 20A but have not adjusted it.  It's in my collection but have not used it other than to see if it works.  I opened it up and it looks much like the ones I have adjusted - two screws with nuts that have to be loosed to adjust the settings.

I know Sunbeam made a tool to adjust the setting, I'm sure they are lost to time at this point.  On the pots I have adjusted I had to loosen the nut that holds the settings in place, then use a very small screwdriver to tweak the adjustment.  Really does not need much.  I found that trying to tighten the nut back always messed up the setting, so I leave it loose.  I adjust the timing as the directions say, 10 seconds after the bowl is dry the high temp should click out, and I set the hold temp to about 170.

As was posted earlier, occasionally, for no known reason my pots will boil over if left on the warm setting. Months would go by with out a problem then I'd walk into a mess with coffee all over the counter and running down to the floor.  Solved it by simply pouring the finished coffee into an air pot.  Stays warm most of the day, and no boil over.

Good luck on adjusting the A series left me know how it turns out.  BTW how is the house coming?