Does anyone care to ask an amplifier designer a technical question? My door is open.

I just want to say thank you Roger. With respect to tube amp output impedance selection, I had never heard that you should “Always use the lowest tap that gives you enough volume without distortion (clipping)”. I have a pair of Kef LS50s in an acoustically treated room (16’ x 11’ x 10’) that I’m driving with a pair of ASL DT200 hurricane mono-blocks (100 watts per channel). I’m not worried about clipping. I immediately tried your suggestion by switching the LS50s from the 8 ohm tap to the 4 ohm tap. And, just like you said, the bass tightened up, so much so that it shifted the tonal balance of the system up. This caused the system to actually sound a little strident. Well, I had used a parametric equalizer to boost frequencies around 10KHz a few decibels to offset the acoustically treated room, I thought. I removed the boost and Voila’, things are noticeably better all the way around.

Hi Everybody,

I’ve got a question for the tube amp designers. How much of a difference does the power transformer make in a tube amp design? Is the output transformer more critical or the power transformer or both? I’ve read that the output transformer is absolutely critical and I know that they can be very expensive. However, how much would it degrade a good design to just go buy an Edcor power transformer, which I’ve heard are decent transformers, and use it with a high-quality output transformer?

Thanks,

I've not tried an Edcor power, I have the outputs. Most of them are made for tube rectifiers I believe. I'm not fond of tube rectifiers in amps above 30 watt, ,certainly not 100 watts. Were you planning a tube rectifier? Which one?

What output transformer might you buy?

===================================================================

Thanks for the response Roger.  When you say "made for tube rectifiers" are you referring to the center tap?  If so, I'm under the impression that I don't have to use the center tap. I'm not an expert but based on what I've read, I'm not a fan of rectifier tubes.  I currently have 2 sets of tube monoblocks and neither of them use tube rectifiers.  One uses a quad of EL34s and the other uses 8 KT88s per monoblock.

As far as output transformers go, I don't have a specific one in mind right now but I would consider an Edcor or Lundahl.  I would only use the latter if I were very confident with what I was building because of the cost.  I would love to know how much difference really exist between the two.

I was considering building a lower power tube amp (25 - 50 watts) if I could find speakers that I could afford that sound good with a medium power tube amp.  The problem is that I keep gravitating towards less efficient speakers.  I used to have Thiel 3.6s and I still have a pair of 3.0s in storage.  I had to move to a smaller room (11' x 16' x 10') a few years ago and I've spent the last 4 years learning room acoustics.  I'm using a pair of LS50s right now, which sound really nice with both sets of monoblocks.  BTW Roger, I still can't believe how much of a difference it made when I moved the LS50s from the 8-ohm tap to the 4-ohm tap on both sets of my monoblocks.