[Alinco] Alinco receive question

[John Geiger]

Thanks for all of the advice on repair places for Alinco equipment.  Maybe the list members can help me come up with an idea as to what might be wrong with my rig.  I have an Alinco DX70TH I purchased used recently, and there seems to be a problem with the receive sensitivity at times.  I use it on 6m but the problem does seem to occur on HF as well.  When I first turn the rig on, everything is fine.  After it has been on a while, the receive sensitivity seems to drop.  It is still usable, but not as sensitive as it should be.  I have a couple of birdies at 50.118 and 50.112 and when I first turn it on they are S6 or S7.  After a while they don't move the S meter any more, but are still plenty audible.  Also, the background noise is lessened.  If I turn the rig off and wait a minute or so, and turn it back on, it is back to normal sensitivity but then drops off again after a while.

Any idea as to what might be wrong with it?

73s John AA5JG