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

Roger, really appreciate your efforts with this post.  But, a question -

"Over 100 watts is only justified by either high listening levels or insensitive speakers or both together. Excess headroom is a myth."

I and many others find headroom seems to relate to clean (undistorted) dynamics.  Would you expand on your myth statement, why you feel that is the case?  Maybe the key is "excess"?

Roger, 

Wow!  What a fast moving post.  Glad to see all the interest.

"There is a lot to this question so lets hear back from you and others."

First off, I suspect many of us non-technical types may not know much about clipping.  I've been aware of it a few times but suspect it occurred other times when I was not certain what was happening.  In my experience I've heard the sonics become thin, hard or harsh, even metallic (as opposed to musical) when pushed to loud levels but before the crack or pop of an actual clip.  I considered that a related but slightly different issue.

When listening for pleasure it is generally in the 80-85 dB range.  But I doubt my RS dB meter is accurate to identify actual peaks so I'm unsure of those.

Regarding amps > 100 wpc, for many years I enjoyed a large pair of Duntech speakers, rated at 90 dB.  John Dunlavy recommended 200 wpc for "full musical enjoyment".  I experimented with a variety of amps (tube and SS) rated from 30 to 300 watts.  I finally settled on a pair of VTL 300 monos for a few years.  That was until I heard Curl's Halo JC-1s, rated at 800 wpc into the speaker's designated 4 ohms.  That was the best I found - musically accurate, solid bass (determined by good recordings of acoustic upright bass), and effortless, unstrained sonics.  To be fair I don't believe the 90 dB efficiency was accurate with such a complex 1st order crossover.

I've since moved on from that system but continue to believe this question of headroom is very important.  Interestingly I remember hearing several times some years ago the idea that within a given line up of amps, the model with 60 to 120 watts was likely the best sounding.

I did have a RM-9 for a few years, one of those few components I was later sorry I sold.

tomic, I have a B&K 707 tester I got many years ago at an electronics swap meet. I really don’t know all that much about electronics but the B&K is easy to use and I’ve found it very helpful in identifying bad tubes -- not just strength but shorts and gas as well.

I would suggest finding a manual for your 667 if you can. Given the age the calibration described there may be beneficial.

Also I've seen positive reports on the Tubes4HiFi kits, including amps.  I have an SP-12 line stage custom built by Don Sachs which is wonderful.  But the basic unit has favorable reports as well.

Roger, lots of good information as well as memories here.  So much in fact it is hard to keep up!

As one of the older audio hobbyists here I too remember these names from the past.  I recall a visit from William Z Johnson at a local dealer to set up his Tympani/ARC system.  Interestingly that same dealer later took on the Fulton line.  Regarding Bob, "Fulton made good sounding stuff. I don't know how but I always assumed him to be a competent engineer with great listening skills.", did you know his involvement with instrument design?  For example I'd read that he designed trumpet mouthpieces.  That was confirmed by an alumni club buddy who played trumpet with a Fulton mouthpiece.  He was so sensitive to colorations in musical reproduction that he assigned a characteristic color (his interpretation) to the unique tonality of each orchestral instrument. 

And I thought the unanswered question was who wants the last piece of pie?

A point on comparison testing which I suspect Roger may agree with.  It is something I've learned after long years in this hobby.

That is a simple A-B is not adequate, even though you may find differences.  I believe at a minimum you need to have A-B-A.  That means any connection improvements (cleaning from friction) as well as differences from something new (possibly a detail not heard in A so B seems better, but it becomes diminished in the overall picture) can be accounted for.

Roger, "What exactly is A-B-A?"

I've seen multiple comparisons where some/many were prepared to offer conclusions after a single switch from an original component (A) to something different (B).  For several reasons I don't feel that is meaningful without at least going back once to the original.  I also thought that was a standardized label but apparently not.