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How hot is hot when moving from class a/b to to a or tubes?

I am considering moving from a class a/b Luxman L509x to a class a or tube amp. 
I have never owned a class a or tube amp, so have no experience of living with one. My kids are hopefully old enough and wise enough not to burn themselves, but I do live in an already warm house with bifold doors leading to a south facing garden. There is no escaping the sun, despite having uv treated glass. 
 
My room is roughly 9 meters by 12 open planed living space. Equipment is, Luxman L-509x integrated, Zu union 6 supreme, 99db sensitivity (this is why I am considering a lower powered tube I can barely turn the Luxman up) music is played roughly 6 hours a day, more on weekends  

who here has moved from class a/b and d to class a with or without tubes. What were the differences of things like:

warming up time 

additional heat to the home

Running in summer time 

additional cost to run

any considerations I should make before purchasing something. I will try in my home, but will need to free up funds 
 

 

mpoll1
jasonbourne52's avatar
jasonbourne52
2,863 posts
 

A true Class A amp will always run hottest with no signal. When playing music the current/voltage goes to the speaker and is dissipated there. The true Class A amp then runs increasingly cooler! A little-known fact that most audiophiles are unaware of! My Bedini 25/25 fulfilled this design aspect as a true Class A amp. In use it always started out extremely hot and ran progressively cooler as output level was increased. Stopping playing music it again got hotter until it reached its bias limit.

jasonbourne52's avatar
jasonbourne52
2,863 posts
 

There are very few true Class A transistor amps. Most so-called Class A amps switch over to Class B after a few watts. A true Class A amp of considerable power will always run extremely hot under zero load and then progressively cooler as output level increases!

mastering92
870 posts
 

All amplifiers can reach their normal operating temperature, but class A amps in general may become warmer internally as if you are driving speakers for up to an hour. If speaker impedance dips, the amplifier will be tasked at supporting them with more current. 

Just make sure you use a Class A amplifier in a dry environment and leave vents unobstructed; so heat loss can occur normally. Otherwise, nothing to worry about...

jonwolfpell
400 posts
 

Regardless of what tube amp you get, I highly recommend if you have kids and/ or pets to get one that has some type of cage around all the tubes! Better safe than sorry for a bad burn or blown amp. 
 

I have a Rogers High Fidelity RHF 200 Mark II w/ two KT - 150 power tubes per side that generate 100+ watts / channel in full class A. Great amp & love it but it gets real hit. I bought the very well made vented lexan cover because I have two very curious cats who gravitate towards warm things. You can still see the beautiful amp & it’s outstanding workmanship but it’s safe! 

decooney
2,104 posts
 

Define your description of what is "hot" to you?.  

I'm re-evaluating this myself again recently. May be helpful to compare w/others.

SS: My full-on Class A 50w solid state amp is said to be operating normally when you can hold your hand on the side heat sinks for about a max of "ten seconds", reasonably. Confirmed by the original designer and recent tech who performed checks and upgrades.  Special grease was added to the OPTs for maximum heat transfer to heat sinks, @47-50c temp max, and recently biased up and upgraded.

TUBE: my two mono block tube amps run two KT150 or two KT120 output tubes per amp. Can hold a hand on the transformers for ~30-45 seconds no issue. Toasty warm but not what others might consider "hot". Will recheck actual temp with infrared laser next wk after re-biasing tubes to their max to see what max heat is. I'd expect higher power 211, 845 triode amps to run a bit hotter in full Class-A.  

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