[tx2sturgis]

For grins I decided to take the temps of these EL34s after about 20 minutes of operation....

Look about right?

Too cool? Too hot?

The probe is about 1 inch from the tops of the tubes.

[Bob in St. Louis]

<.....Adds this to the list of "how to tell if you're an audiophile".... >

[tx2sturgis]

<.....Adds this to the list of "how to tell if you're an audiophile".... >

Well yes but....

There is a backstory here. Short version is:

No biasing instructions on this amp.   Bias points not marked or obvious. Did some tube rolling, bias adjustments, and ended up with a red-plating tube and a hot smell from the amp.

Ooops...

Also the power transformer was getting hot, not just warm, after a few hours.

Figured I'd balance the tubes at least. Amazing temperature differences when I first tested them...Looks better now...at least to me. And yes, the amp sounds good...but it sure sounded funky on the right channel when that tube red-plated!

Anyway, seems to have survived and playing some classic rock as we speak.

[Bob in St. Louis]

No worries, I could help but to give you a poke in the ribs.....from one "phile" to another. 

[FullRangeMan]

For grins I decided to take the temps of these EL34s after about 20 minutes of operation....

No probe, you need a ray thermometer.
http://www.amazon.com/Fluke-62-Infrared-Thermometer-Battery/dp/B0089N2ZH6

[Steve]

Hi TX,

The max temperature should be measured at the side of the tube, where it is the hottest. Probably where the plate is closest to the glass. Maximum temp for most, not all though, is usually around 200-250 degrees C, or 390-480 degrees F, but check the individual tube specs. Some mention the seal temperature, but that is usually transmitting tubes.

Cheers and good luck.
Steve

[tx2sturgis]

No worries, I could help but to give you a poke in the ribs.....from one "phile" to another. 

Sufficiently poked...

But I searched the net and this forum and couldnt find much about tube temps...I took readings on another self-biasing amp that I have and the little EL84's showed about 345f to 360f....

Now this got me thinking...(.which could be dangerous and cause smoke!)

Everyone biases tubes based on current and voltage readings...and maybe wattage vs distortion vs 'tone'...

I just wonder where or how might temperature be an additional indicator? (in the olden days, they didnt have IR guns)

Of course, air blowing over the tubes, and different IR guns held in different manner and pointed at different parts of the tube will show differing temps.

But if you looked at two tubes in a push pull or single-ended amp and one showed say, 225 degrees and the other 'matched' tube was showing 375 degrees...would this be normal?

I would think not.

I wonder if we will see a few 'audiophiles' taking tube temps....

Just a thought.

[tx2sturgis]

Hi TX,

The max temperature should be measured at the side of the tube, where it is the hottest. Probably where the plate is closest to the glass. Maximum temp for most, not all though, is usually around 200-250 degrees C, or 390-480 degrees F, but check the individual tube specs. Some mention the seal temperature, but that is usually transmitting tubes.

Cheers and good luck.
Steve

Thanks Steve, I did notice the temps were the hottest at the sides, adjacent to the plates (ranging up to about 300-320f...but I sort've figured that the 'hotspots' were not as usable as the average temps....measured near the top, approximately adjacent to the top mica insulator, and below the silvered coating.

At any rate, measuring each tube in the same spot seems to yield the 'balance' I think I was looking for. I did notice that very small changes to the bias pots make a very noticeable difference in the tube temp after a few minutes.  Hmmmm....

Again thanks.

[FullRangeMan]

Thanks Steve, I did notice the temps were the hottest at the sides, adjacent to the plates (ranging up to about 300-320f...but I sort've figured that the 'hotspots' were not as usable as the average temps....measured near the top, approximately adjacent to the top mica insulator, and below the silvered coating.

At any rate, measuring each tube in the same spot seems to yield the 'balance' I think I was looking for. I did notice that very small changes to the bias pots make a very noticeable difference in the tube temp after a few minutes.  Hmmmm....

Again thanks.

This thermal 6C33 video confirm it:
https://www.youtube.com/watch?v=EaWHqNy7_5c

[Steve]

Thanks Steve, I did notice the temps were the hottest at the sides, adjacent to the plates (ranging up to about 300-320f...but I sort've figured that the 'hotspots' were not as usable as the average temps....measured near the top, approximately adjacent to the top mica insulator, and below the silvered coating.

At any rate, measuring each tube in the same spot seems to yield the 'balance' I think I was looking for. I did notice that very small changes to the bias pots make a very noticeable difference in the tube temp after a few minutes.  Hmmmm....

Again thanks.

Your quite welcome TX. I should have mentioned that that is usually the absolute maximum high temperature on most tubes.

Cheers and good luck.
Steve

[c1ferrari]

Look about right?

Too cool? Too hot?

Can you source the temperature rating(s) from an RCA tube manual or something similar

[c1ferrari]

No probe, you need a ray thermometer.
http://www.amazon.com/Fluke-62-Infrared-Thermometer-Battery/dp/B0089N2ZH6

That looks like a nice tool...thanks for the link. 

[FullRangeMan]

That looks like a nice tool...thanks for the link. 

I have this basic model but it dont own blue back light display as the picture suggest.
This image is from a upper model.

[c1ferrari]

^^^ Thanks. 

[tx2sturgis]

Can you source the temperature rating(s) from an RCA tube manual or something similar

Just for info...If you measure lower on the tube by the plates its a lot hotter but the hot spots vary widely as you move the tool around. It seemed to be a bit steadier on the readings when I measured about 3/4 way up the tube, above the plates, but below the getter.

The tool I used is called a RayTek MT4, around $60 locally....of course there are cheaper and more expensive units out there.

[c1ferrari]

This leaves me curious as to the protocol used by the manufacturers to establish the measurement 

[E55l2]

Just a small warning for everybody who uses an IR-gun. An infrared gun measures not the temperture but the infrared emmission. There is a relation between temperture and infrared emmision but sometimes this can go horribly wrong.

Because  the gun measures the spectrum you should know what kind of emmision spectra your object (in this case the tubes plate) is radiating. Most ir-guns are calibrated on carbon black objects and more expensive guns you can choose the radiation patern of the object.

I did recently a measurement of my -chrome plated- espresso machine and i know for sure it is very hot, about 93 degrees Celcius, but with a standard ir-gun i measure just 35 degrees.




 

[c1ferrari]

Indeed...good info -- thanks!

[tx2sturgis]

Because  the gun measures the spectrum you should know what kind of emmision spectra your object (in this case the tubes plate) is radiating. Most ir-guns are calibrated on carbon black objects and more expensive guns you can choose the radiation patern of the object.

Yeah its not an absolute lab measurement in any case....just for reference, the IR gun that I used measures the glass surface IR...it has no way to see the plate....the aiming laser does, and the human eye does, but the IR gun only measures the IR of the first surface....the glass.

[c1ferrari]

What do folks think about using thermal imaging technology for measuring tube temp?
One could apply the instrument to determine where there's heat exchange, e.g., doors, windows, attic insulation, etc., ... tube temp?