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more reliable amp: tube or solid state class A

i got to reading this thread:

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1144724173&openfrom&1&4#1

i require no convincing that class A sounds better than AB or D or whatever else, but the efficiency is terrible, with the efficiency losses being reflected as heat.

and heat, as we know, causes thermal breakdown. this is a matter of engineering: the hotter a component runs, the shorter the mean time between failure. simple stuff.

but here's the question: if we took 2 equally hot-running amps, one tube and one SS, over the long haul, what would be more reliable? the tube amp, or the SS one?

i'm thinking the tube amp, solely b/c the tube is the hottest part, and its failure is accomodated for in the design (you simply plug in another tube). a hot running SS amp will eventually burn out resistors / transistors, and joe audiophile will be forced to send that to the factory for replacement.

(i am going to do some HVAC work on my room, and if i can keep in cool in mid July, i will be moving to the winner of this argument)

thx
128x128rhyno
herman
1,974 posts
 
A well designed solid state amp will always be more reliable than a tube amp. Properly designed means that the output transistors are operated well below their maximum ratings, and will therefore last a long time. Properly designed also means that the heat is directed away from the rest of the amp. On the other hand, tubes will always burn out after some time. I am firmly convinced that a tube amp will sound better but if reliability is the criteria then SS wins.
gregm
3,021 posts
 
A fifth support for SS. Maybe the right word is "maintenance" rather than "reliable" in this case. The tube will need some maintenance -- i.e. first of all, changing the output tubes every 2-5k hrs.

The SS (and tube) requires changing the lytics -- every ~6-10yrs (more like the latter).
rlawry
414 posts
 
I agree with the solid-state Class A amp also. Not because of the circuitry, which can be equally robust with both types of amps, but tubes are unreliable, especially output tube types that have limited lives and can become noisy, etc. If the heatsinking is done correctly on SS amps, they will take the brunt of the heat and any damage is localized to the sinks. If you really want to feel heat, try some OTL tube amps. I had some Fourier Panthere monoblocks that used 8 6C33CB output tubes with cooling fans--these things drew 5-6 amps at idle and doubled as space heaters. The unfortunate effects were a lot of internal heat damage, especially tube sockets.
ngjockey
1,042 posts
 
I've yet to hear any evidence that class A is any less reliable. I've only heard opinion and presumption. I've had many A/B and A amps over the years and the only one that burnt out any transistors (FETs) was A/B. The Plinius amps I have now have been constant since October in class A. Cheaper than running the furnace.

Let me know when a tube amp comes with a 20 year warranty. On the other hand, it's easy to change a light bulb.

There are many A/B amps that are excellent that you will be limiting yourself from. If you're speakers are a demanding load, A/B might be the better choice for the dollar.
aball
1,994 posts
 
If I understand your question correctly, as an EE, my vote goes to the tube amp. Tubes are the hot parts of the amp and are outside the "box" in most cases. Heatsinks will invariably heat the amp and the capacitors inside it which will not be good in the long run. The capacitors are the parts that hate heat - not so much the transistors or tubes.
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