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Living With A Class A Tube Amp

I'm ready to replace my venerable Prima Luna Dialogue One amp.  Just as I thought I had my choices sufficiently narrowed down, I came across Roger's EHF-100 integrated amp.  It has the features I'm looking for without any frills, and has sufficient wattage to power my Sonus Faber Sonetto VIII speakers   Checked out their web site and had an informative email conversation with Roger, who confirmed that this would be a good amp for my speaker. s and room.  He provided me with some useful information, but I need some info from Class A tube amp owners generally.

From what I gather Class A amps produce max power at all times, therefore run hotter than a typical amp.  How does this affect amp placement?  My current amp is on a heavy wooden table and in front of a curtained window.  Would the table need to be replaced?  Do I need Nomex curtains?   How does this heat affect tube life?  Any other internal components subject to accelerated aging due to the heat?  Any other thoughts from Class A amp owners would be greatly appreciated.

Thanks,

John Cotner

New Ulm, MN 

jrcotner
noromance's avatar
noromance
9,766 posts
 

I can't believe there is a guy called Roger at Rogers High Fidelity. 

jrcotner OP
68 posts
 

Thank you for all of your responses.  I sifted through them and here's what I've been able to discern:

  1. Class A amps produce more heat than typical amps.  Placement may need to be considered depending on wattage and style.
  2. The additional heat may reduce tube life by as much as half. 
  3. Operating costs will be higher due to more frequent tube replacement.
  4. Class A tube amps have desirable sonic qualities, but other current tube or solid state amps can produce equally good sound quality without the drawbacks listed above.
trivema's avatar
trivema
84 posts
 

I have 4 single ended amps, 2 SET (triode), 2 SEP (pentode) ranging from 8 wpc to 23 wpc driving several different speakers that range from 88dB to 99dB sensitivity.  I’ve never had the volume pot on the 23 wpc “beast” past 11 o’clock on any pair of speakers I own.

The Sonus Faber VIII looks to be 90dB sensitive, and the Rogers @ 55 wpc. Unless you’re seeking concert hall or jet engine sp, the Rogers should drive the Sonus Fabers just fine.  You’ll likely only push 10-12 watts, or less, at normal listening levels, its the dynamic transients that you need extra headroom for.  
 

Rogers specs the EHF 100 @ .01% THD @ 55 watts, which is incredibly low for a tube amp. A good 300b SET will hit 3-5% THD at 8 watts. You’ll have little to no distortion or clipping with transients with those specs. Rogers looks to be a very solid build, my guess is it would drive the h**l out of the Sonus Fabers! 

jlbkmb1958
28 posts
 

I use a push pull with a quad of KT88 tubes; it consumes about 2-300 W and has an output of about 35 wpc. I definitely generates some heat. The tubes themselves are like exposed light bulbs. The majority of the heat seems to come from the transformers. Mine sits on a shelf with at least 6 inches of free space around it and nothing above. If you put a hand within about a foot, you will feel significantly radiant heat. 

audioaholic1
8 posts
 

I second having Brandon build you a pair of SET amps.

The tubes will last a long long time. 
I’m powering my 92 db speakers 4 ohm with  833 monoblocks at  33watts per channel and they have more thanks enough power. 
 

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