What are the weak points of Pass amps and pre-amps ?

I remember running a Yamaha 1970s CA 1000 integrated amp with 15 watts Class A switch.  It got rather warm but it did sound superior to the Class A/B 70 watts (about).  The 15 watts sounded more musically involving, smoother and quieter than Class A/B.  

I own an EAR 890 which is 70 watts Class A.  It gets burning hot on the chassis and transformers after 30 minutes. 

I now use a pair of monoblock 130 watt tube amps running Class A/B.  It is a voltage regulated design which runs so cool that after 2 hours, you can place your hand on the transformers which are merely warm.  Plus the sound is superior to the EAR 890.  

I don't think there is an advantage running Class A over Class A/B, depending on design.  The cost of powering Class A and the heat are definitely a consideration.

Note, one could fry an egg on a hot EAR 890 amp, it’s that hot for the chassis and transformers, dangerous to touch after 1/2 hour.  Pass amps currently list their temperature at 127 degrees, above warm and slightly hot.  

Wow, I didn't think that an amp was so sensitive to ambient temperature and vibration/movement that it would affect bias (for a solid state amp yet)!  I don't like touching the insides of an s.s. amp to adjust the trim pots with meters while on.  Yuk! 

I have extensive listening to a high end Ypsilon preamp a new friend's home.  That and High Fidelity cables had me run from his listening room the first time.  After replacing the horrible cables, the preamp was the next culprit of an $850,000 system in producing bad sound.  It was replaced by a VIva pre-amp.  I doubt Pass pre-amps could sound as bad as an Ypsilon.

The Ypsilon preamp and phono preamp were driving Viva tube amps which were driving Avantgarde Trios and 3X Basshorns. Yuk! Switching out cabling from High Fidelity to GroverHuffman cabling made it listenable but still rather thin, bright and forward. Substituting Viva preamp and a custom designed tube pre-amp, wow, the sound mellowed and became enjoyable. We suspect that the phono preamp is also on the bright and forward side using a Kiseki on a Caliburn/Cobra setup. We also tried CDs. I know, Michael Fremer owns and believes the Ypsilon to be his favorite. Maybe in his system but not in the one I heard.