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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
immatthewj
2,042 posts
 

no need to bias tubes.

Don’t you still have to adjust the bias on the one output tube per side that you do have? That is, unless it is self biasing?

audioman58's avatar
audioman58
4,169 posts
 

You most likely have either ultralinear or pentode 

pentode being a purer circuit without all the feedback as in a Ultralinear circuit.

noromance's avatar
noromance
9,820 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
90 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! 

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