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

@fleschler  ramtubes - So, you don't believe power cables make a difference other than connectors and isolation transformers are worthless? Is that correct?

Do I detect a little nudge there?  I think isolation transformers are great when needed. I like balanced power which also isolates. These things have a good chance of reducing noise if one has noise.

My stand on power cords is entierly intellectual from an amplifier designer and transformer makers point of view. I know what is inside a transformer and how it works. When you know about transformers, house wiring etc. we can further discuss this interesting topic. 

"Musicality" is one of those oh-so-subjective terms with no agreed-upon meaning. But the same can be said about the incomplete sentence by khiak above ;-) . The "can" implies it is a question, but the "changes" negates that. Should the sentence read "Can changing the power cord to the amp change the musicality of the sound at the speakers?" (a question), or "Changing the power cord to the amp changes the musicality of the sound at the speakers." (a statement) ?

@ atmasphere
In one post Roger says it doesn’t make much difference, OTOH in the very same post describes the power cords that he made up special and how anyone can do it. I have to assume that he felt it was worth doing

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Ralph, what is OTOH mean? Im a newbee.The cords with diodes make a difference when needed. I think I have been clear and consistant here.

Your amp draws heaps of current when played hard. Something heavy ga might help a little at full power. At idle Im not so sure. I note the current draw of the M-60 goes up quite a lot at full power testing.

How long can I run an M-60 sinewave at 60 watts into 8 ohms before the tubes get unhappy?

@prof 

I could really use some help betting a better grasp of amplifier/speaker interaction. Specifically, in what sense a speaker is "easy to drive" for an amplifier.

This seems to generally relate to two parameters:

1. Speaker sensitivity
2. Speaker impedance (and phase angles etc).

I’ve seen speakers with higher sensitivity but lower or wilder impedance termed "easy to drive" and speakers with lowish sensitivity but higher and smoother impedance being "easy to drive." So I’m trying to get a grasp on what it means...in practical and possibly sonic terms...when a speaker is "easy to drive"for an amplifier and what you get when trading off sensitivity vs smooth impedance.

To turn it in to a practical example:

I owned the Thiel 3.7 speakers. Here are the Stereophile measurements:

https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements

Note the 90.7dB sensitivity, but with it seems a fairly challenging impedance.

***********GREAT QUESTION, EVERYONE READ THIS**************

Ill take this one speaker at a time. The 3.7 is THE speaker that birthed the RM9-SE and RM-200 designs. Those are AB2 designs that use positive grid voltage to extend the output current range of an AB1 amplifier. We had a MK1 RM-9 customer who was going through output tubes at an alarming rate. The speaker and his love of Miles was driving the tubes hard.

First, JA did not point out, as he now does that 2.83 volts is NOT the proper voltage for a 4 ohm speaker. Its 3 dB too high so the 4 ohm sensitivity of the 3.7 is 87 db. Its even worse because this it a 2.5 ohm speaker so take off another 2 and make it 85 dB. So its really not a very efficient speaker.

I made the RM-200 with taps down to 1 ohm for speakers like this to preserve the damping, reduce the tube stress and lower distortion. The 2 ohm tap on the RM-200 is ideal for this speaker. Mismatching the load on a tube amp makes it work really hard. This is a 2.5 ohm speaker so good luck. Many SS amps will not play this speaker well.

Thats your the gist of question #1. 

#2. Phase angle..

As the phase approaches 90 degrees the output devices have both full voltage and full current across them. The dissipation in SS or tube amps goes wildly high. SS amps are sure to current limit, tube amps just take it. This is why tube amps have a reputation for driving such loads at the 3.7 and ESLs.

Thats all for now. This great question deserves several parts. Anyone please feel free to ask as we go for clairfication.

"Musicality" term used to express a fatigue free listen . Still as resolving as anything but probably not boosting any frequencies . Hence fatigue free . No distortion as well .