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RE:Pros and cons of your 211 amp?

You'll never experience the joy of a 211 using Chinese parts (especially output transformers). Here's more food for thought:

The dirty secret of SE amps is that most of them produce much less power in the first two octaves than what they're capable of at upper bass and midrange. This is usually hidden by publishing specifications showing only low-power frequency response and a maximum output number taken at 1kHz or so.

For example, my A2 211 monos are capable of 25-30W (depending on bias) at 1kHz. However, that falls to 15W at 40Hz and only 6.5W at 20Hz without feedback. Adding 5dB of feedback pushes the 20Hz number to 10W. This is more than sufficient for my speaker system (which I used for years with a much smaller 6V6 SEP amp), and the musical presentation is superb. Nevertheless it highlights the typical results when using a series-fed SE output transformer. I'm using Peerless/Magnequest FS-100 specified for 30W, and I can tell you they are large and heavy. If these transformers were used with a smaller tube, such as a 2A3 or 300B, the natural power limitations of the output tube itself at midrange would render the LF rolloff less prominent. Of course, no one uses 30W transformers for an 8W output tube. Transformers capable of flat response with a 211 or 845 from 20Hz to 20kHz would be the size of cinder blocks.

My point is that you should evaluate your speaker system, listening environment and budget carefully before jumping into the large SET arena. I will probably never build another SE amp unless it's very small and designed for a specific purpose (such as a headphone amp). OTOH, I believe Class A push-pull resolves these issues, so that's a direction I want to explore in the future.


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