Tube DIY Asylum

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The resistor....

Posted by Lew on July 14, 2017 at 09:12:15:
Are you saying that the once 8-ohm, now 25-ohm resistor is in parallel with the output of the amplifier that is being auditioned? I was previously under the impression that only the amplifier NOT connected to speakers was seeing the load resistor. So, even if the impedance seen by the amplifiers is now likely to be within a reasonable lower limit (for an SET, greater than 8 ohms), there is still the probability that the resistor is coloring the sound. Please don't be angry, but this is just not a good way to evaluate an amplifier, let alone to compare two amplifiers, in my own opinion, of course.

To lessen the resistor effect, you could use a much higher value, like 100 ohms. Or better yet, re-arrange your switching such that only the amplifier not connected to the speakers is instead connected to the load resistor. The latter might require two switches but could be done easily. At that point, you may be able to perceive differences that thus far elude detection.