Power cable dilemma

Electronic components that have been sitting unplugged for an extended period should be run up on a variac before use to prime the power supply caps.

So cable deniers don't believe you need a heavy gauge power cord.  I am a "cable denier" of sorts in that I think that 99% if not more of the gain available in a cable can be achieved with an inexpensive but heavy gauge cable.   

You have described the exact symptoms of too light a power cable.  

I'll tell a quick story. In my tube amp journey I wanted to try a Decware amp.  There is a 2 year wait list for decware so I started looking on the preowned market.  Being an early riser, I found one listed late saturday night and bought it at 0400 Sunday morning.  It was an unpretentious and relatively inexpensive SET.  It was only 6 wpc (SE34I.5 for those curious).  When the ap arrived there was a note with it "I have included an upgraded power cord I bought for this amp".  It was obviously very light.  I looked it up, it was only 16 awg and cost $300.  This guy had "upgraded" his power cord and ruined the sound from his amp. I was very fortunate to benefit from his misfortune. this amp excells and I eventually upgraded to a top end Decware amp.

As a physicist, I see many examples of google educated scientiists missing the mark and shooting themselves in the foot.  Most tube amps are a 200 watt load or less.  Look at the book and you'll see that 16 awg is plenty for a 200 watt load.  (I think that amp was closer to 100 watts),  But dynamics and base require the ability to supply very high currents for very short times.  Overall it averages out to 100 to 200 watts, but for short times much higher current is required.

Jerry

I don’t think it was due to the caps needing to power up. I had run the amp the previous day for about an hour, but at lower volume as background music while we cleaned and decorated the room for a party my wife was having. The caps should have been charged sufficiently. Also, if they were not charged, for them to suddenly become charged at the exact moment I substituted the power cord, would be an unbelievable coincidence. 

In thinking about my experience with this cord, I may have discovered another instance of something odd occurring. I purchased a Line Magnetic LM150 integrated tube amp. It was borderline powerful enough to drive my speakers based on the specs. When I put it in the system, it performed very well. I kept a close eye on the meters to be sure the amp was not getting too stressed. The peaks never went higher than 50%-75% on the meters. I ran the amp for about three weeks and added some new ribbon speaker cables. Much to my dismay, at similar or lower volume levels I noticed the meters were pegging out. I attributed it to the unusual impedance of the speaker cables. I pulled the amp temporarily and ran a beefier solid state amp for a bit. Fast forward a month later and I tried the LM 150 again. This time the meters behaved as they did at first. I was both relieved and puzzled. I have had the amp in and out of the system numerous times over the past couple months and sometimes the meters are fine and other times they max out. I honestly do not remember what power cords I was using each time, but I’m going to guess there is a correlation between the meters maxing out and the “bad” power cord. This will be an easy thing to check. 

I would recommend you use a quality 10 gauge power cord, like a Kimber PK10 and use the balanced connections to your preamp.

Are you using the single ended inputs or balanced inputs? If single ended inputs are you using the shorting straps between pins 1 and 3?