question for SLP05 owners:

The reason Cary Audio changed the plate on top of the power supply to one without “foot indentions”, was to discourage people from stacking for the sole reason that sometimes the transformer radiated noise into the preamp above.  When people would complain about hum being radiated into the preamp from the power supply, and we’re told to move the power supply away, they would question “then why are there indentions on the top plate for it to be stacked?”.  So Cary Audio changed the power supply top plate to one without indentions so people wouldn’t stack them or question anymore.  Thus, no more hum issues. 
Heat typically wasn’t the problem although they do get hot because of the rectifier tube in the power supply.  The power supply umbilical cable was made by Kimber Kable for Cary Audio and is pretty good non-shielded wire. 
Some people change the rectifier tube to a solid state type (for sound change purposes) which also runs cool and can make the preamp sound more detailed with much tighter bass.  It’s something to play with you like.  I use SS rectification in mine using high speed rectifiers. Not HexFRED’s but similar. I had an old “Weber Copper Cap” that I upgraded the rectifiers in that just plugs into the octal socket in the power supply.  You can use one of those made by TubeDepot or whatever.  In my system I love the speed, imaging and detail it presents but every system is different. If you already have an overly bright sounding system you probably won’t like SS rectification on your SLP-05.  

 

@lwin They were made to be stacked . I recently sold mine to a buddy who has them stacked just like I did for years.

@harpo75 The reason Cary Audio changed the plate on top of the power supply to one without “foot indentions”, was to discourage people from stacking ...

And yet another photo of the indentions, and not stacking. If the indentions on the power supply top plate were removed - there is a reason for it as @harpo75 suggested. Worth doing more research on this topic, sometimes designs change for a reason. I bet the warranty decision maker at Cary Audio can share updates on what’s important to make the gear last longer. They see the incoming repairs.

@immatthewj no experience with Cary but when I had Pass Labs XP-22 two chassis preamp I heard a very subtle improvement when I separated the preamp from its power supply chassis. Neither one of the units got hot by the way. Slightly warm. I would keep the Cary preamp unit away from its power supply for reasons to not pollute the preamp unit with EMI that the power supply generates and to give the two units space to get proper ventilation.

Thanks for the input, @everyone.  @decooney , as far as the rectifier tube, it came with a Sovtek installed, I tried a Gold Lion for a short time, then a UK Amperex (which I am told is basically a Mullard that was branded Amperex) and recently when I was moving some stuff around to try out a high pass filter in my chain I put the Gold Lion back in.  It gets quite warm, with all of them.

After posting this thread/question and evaluating everything, I am going to continue to find a way not to stack them--for both the possible EMI and the temperature that makes me a bit uncomfortable about the idea.  

I don't remember it getting hot, but it was at least 15 years ago since I had the SLP-05 so take that with a grain of salt!