Does altitude affect running temperature

[super&plexi]

I usually run  my stuff around sea level, ( home and gigs)but  lately have been at about 6500 feet, and noticed my super Reverb rectifier glowing really yellow on the plate and the amp running much hotter than I'm used to, and PT was quite hot.  Wall AC was 121 and usually ran 119 - 122 in California. Quite often I would run it through a variac at 1:10 or so but just as often would run straight in the wall /Mains and never remember it being this hot. I guess I'll open it and see what's up but if the consensus is that things run higher at higher altitude and the seemingly larger glow in  my rectifier may not be cause for alarm that I may just slip it back on the variac and turn it down some. Any thoughts? Thanks.   Also I really like the variance in rectifier choices in regards to voltage drop and wonder if adding solid state diodes for safety would change  much. Am I correct in assuming unless it's a FWB that it would only further lower B+ X a volt or so, which would be fine. I just wouldn't want any raises in B+

[trobbins]

Convective cooling relies on the mass flow of air past the parts to transfer away heat as an increase in air temp.  If the density of air is noticably lower then the ability to cool parts is less, and hence their nominal operating temp increases to compensate (ie. radiative and conductive transfer now takes away a higher percentage of the heat transfer).

[p2pAmps]

In my younger days I played many tube amps in Lake Tahoe NV and never had issues with hot running amps.  I believe Tahoe is between 6-7K feet. 

[drgonzonm]

Yes to altitude, and yes to safety diodes. 

Humidity also has an effect

[sluckey]

Just a bit of trivia... Many mil spec transformers actually had a max altitude rating that means the transformer was tested and guaranteed to operate up to that altitude.

[Paul1453]

Lots of old military parts seemed to have an altitude rating.
I'm guessing that was necessary for use in aircraft.

I don't think that altitude has an effect on magnetic fields though.   

Our transformers work on those magnetic field principles.

As was mentioned, air density may have an effect on the cooling properties of the air flow.
I suspect that thinner, drier air could cause your gear to run hotter.   

[drgonzonm]

I suspect that thinner, drier air could cause your gear to run hotter.   

When one discusses humidity, one discusses the partial pressure of water, which is temperature dependent.  The higher the humidity the lower the density of air.  Dry air has an average molecular weight of about 29.  and water has a molecular weight of 18.  So as humidity increases, air density decreases.  (I got lost finding info on the specific heat at constant pressure for air and water vapor)

I'm voting your gear runs hotter at higher humidity. (relative humidity) 

[Paul1453]

I suspect that thinner, drier air could cause your gear to run hotter.   

When one discusses humidity, one discusses the partial pressure of water, which is temperature dependent.  The higher the humidity the lower the density of air.  Dry air has an average molecular weight of about 29.  and water has a molecular weight of 18.  So as humidity increases, air density decreases.  (I got lost finding info on the specific heat at constant pressure for air and water vapor)

I'm voting your gear runs hotter at higher humidity. (relative humidity)

I'll accept that scientific evidence.   

My question is the cooling value of the humidity, if any.
I theorized that the higher humidity might cool things better.  Maybe not?

[trobbins]

Trying to gauge the effect of humidity is probably 'down in the noise'.  The density of air is lower (as humidity increases), but not by much relative to the altitude increase being described.  The radiative cooling performance may well be a titch better with increased humidity - but that would be splitting hairs also.


A dirty glass envelope, or surrounding nearby objects that have a hot surface, or locating the amp such that free air flow is more restricted than before, or the sense of temperature is skewed by the OP being in a different climate and altitude, are probably bigger concerns.  Or as inferred, a fault has developed during transport between countries.

[drgonzonm]

I am revising my thoughts, equipment should run somewhat cooler at higher relative humidities.  The Cp for water vapor is about 1.86
for room temperature and the Cp for air is about 1.  all from the net. 

Just don't pour beer on your amp to cool it.