What are the advantages to a Class A amp & what are the trade offs?

That's where you are 100% incorrect.  That Dynaco is NOT a typical unit. It has been modified to have superior control of deep bass.  My friend Robert Pincus and Audiogon poster Oregonpapa know how powerful my little Dynaco amp is.  It is not as refined as my 130 watt monoblock Class A/B tube amps are, but the voltage regulation, non-ultralinear type is based on the same design concept.  You have never heard a Dynaco ST70 like mine.  The EAR Class A amp has a very poor damping factor and cannot tolerate my Legacy Focus speakers.  Both my Dynaco and mono-blocks have feedback, variable feedback for the mono-blocks although the designer said it was about 6 to 8 db global type at its minimum which we like best.

jspohn - I own an EAR 890 70w Class A zero feedback amp.  It does not have sufficient power for my Legacy Focus speakers which has a tough impedance and 6-12" woofers.  My highly modified Dynaco ST 70 with 30w Class A/B kills it on the focuses (tremendous bass control and dynamics).   When playing both amps on my Legacy Signature IIIs with an easier impedance and 6-10" woofers, the two amps sound very, very similar.  From this experience, I found that a Class A, very hot amp does not deliver into low impedance and/or big driver cones despite a smaller amps Class A/B design (not ultralinear but voltage regulated transformer tap design).  

I have several Yamaha CR620 35 watt Class A/B 1978 receivers that sound excellent and can drive the Focuses just fine (Tom Port of Better Records recommends this pairing).  I use them on smaller smaller speakers for my two video set-ups.

Excuse me, but what is an F5 amp?  I can't find it in this thread.          I found excessive global negative feedback is also not my preference.  I like the VAC Class A/B amps with 6 db of same.  

Wasn't the XA25 the amp with superlative technical reviews?  Thanks for the info.

Well, I have had some quite powerful small Class A/B amps which deliver 2-3X their rated power. Not only that, but they are about 3X to 5X as powerful on a wattage rated basis as many solid state amps.
The earliest amps to sound super dynamic is the McIntosh MC30s. Next are my highly modified Dynaco’s which can deliver huge and clean bass dynamics into low impedance loads. Lastly, my custom built Altec transformer based 130 watt amps which could drive anything a 500 watt solid state amp can. Maybe my Class A/B amps aren’t as refined in the mids as the best Class A tube amps I’ve heard, but I can put my hand on my big amps transformers hours after being played hard while I could burn my hand in 15 minutes anywhere on the chassis of an EAR 890 70 watt Class A amp which can’t handle low impedances.

My 70 watt Class A EAR 890 has 8 itty bitty storage capacitors while my 130 watt Class A/B monoblocks have huge 3" X 7" pair of storage capacitors each. The McIntosh MC30 sounds like it is 3X or 4X more powerful than it’s rated. My voltage regulated Class A/B amps can drive low impedance speakers with ease, stay cool and sound great. Maybe they are inferior in some sonic ways, but they are superior in most others. I will stick with my amps and you can have your F5 which I am not sure is a single ended or push-pull design. The great sounding, huge and hot Class A tube amps I’ve heard are usually single ended.

The Jazz Bakery isn't an ideal sounding venue.  I've frequented it half a dozen times.  Bob Wilber played there a decade ago and his sax and clarinet sounded peaky and bright, actually aggressive sounding, so unlike his playing style.  Locally, many churches and concert halls have great acoustics.  The absolute worst with a 5 second reverb time is the Queen of Angels Cathedral.  I've sung there four times and I couldn't hear myself in the choir with all that reverb.  My wife said it sounded like mush.