Thermography on 6C33C/6C18C aka. 6S33S/6S18S - diyAudio
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Old 8th March 2013, 05:53 PM   #1
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Default Thermography on 6C33C/6C18C aka. 6S33S/6S18S

Some days ago i did a thermography on those 6C33C/6C18C aka. 6S33S/6S18S, just to see how they warm up/cool down and behave on forced cooling.

I summed up the informations in a short video shown here:
Thermografie / Thermography Heat Russian Tube Röhre 6C18C 6S18S 6C33C 6S33C - YouTube

As the information-plots are in german, just ask for the things which aren't clear to understand. For the counter - it runs in seconds.

Regards,

doc
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Old 8th March 2013, 06:08 PM   #2
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Nice equipment. Thanks for posting.
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Old 8th March 2013, 09:01 PM   #3
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Were you able to calibrate the temperature scale? Was the calibration at room temp only?

Of significant practical benefit if you get inclined, is to have two tubes on, and identify the increase in temperature on the area of glass between the two tubes, compared to the other side of the tubes.

Did you also take some video of the power tube next to the preamp tube. That would also indicate the temperature rise of the preamp tube glass that is next to the power amp tube.

Were you able to do a graph of the glass surface temperature as a function of tube internal power dissipation, at various levels of power dissipation?
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Old 9th March 2013, 06:56 PM   #4
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Quote:
Originally Posted by trobbins View Post
Were you able to calibrate the temperature scale? Was the calibration at room temp only?
The camera is calibrating itself, so no need to do so.

Quote:
Originally Posted by trobbins View Post
Of significant practical benefit if you get inclined, is to have two tubes on, and identify the increase in temperature on the area of glass between the two tubes, compared to the other side of the tubes.

Did you also take some video of the power tube next to the preamp tube. That would also indicate the temperature rise of the preamp tube glass that is next to the power amp tube.

Were you able to do a graph of the glass surface temperature as a function of tube internal power dissipation, at various levels of power dissipation?

For the first two, i don't have taken such measurements, For the last, i did. So theres one without anode voltage applied @1:14, and another one with 195V@220mA at the anode @1:52.

Thats measures 118°C vs. 215°C.
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Old 9th March 2013, 10:32 PM   #5
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All I can suggest is to not take the temperature measurements as absolutely accurate, but rather to mainly use the 'relative' temperature changes as the merit in doing the experiment.

Did you decide the emittance value to apply? From what I can summise, the emittance level will change with temperature and other aspects of the glass envelope of the tube. A good indicator of this issue is in the link:
http://ircon.com/web/pdf/an109.pdf

My suggestion for the last comment was to do a graph, a plot with a number of measurements, so as to indicate the character of the relationship between glass surface temp and Pdiss (eg. linear character, or otherwise). I can't recall if the heater power was identified.

The fan-forced test was interesting. From a 'thermal resistance' perspective, it would again be great to get a small number of measurements where the air speed was measured and changed.

But you may not have access to the experimental setup again?

Ciao, Tim

Last edited by trobbins; 9th March 2013 at 10:35 PM.
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Old 10th March 2013, 02:11 PM   #6
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Well, we had choosen epsilon at 0.93 for quarz glass. For sure, temperatures can't be assumed as absolute values, just because the tubes glass surface isn't a black body.

Thanks for the link!

The heater power is assumed to be 3.3A at 12.6V.

I could do the measurements again, but actually don't have the time nor the passion to do so.

Regards,

doc
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Old 10th March 2013, 11:45 PM   #7
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No probs about extra measurements - my suggestions were just a wish list if you were keen to pursue the topic.

The subject is complex, and so it is easy for people to take away a wrong message about absolute temperatures when looking at the video and seeing spot temperature values, and taking them as fairly 'accurate' because the equipment costs a lot and its a university setting and there are technical values floating all around the presentation.

It's not that the glass surface isn't a black body, as the emittance covers that, but the emittance is complex and varies with glass type, glass thickness, and glass temperature. And there may be an even more complex contribution if there is a higher temperature object behind the glass (ie. you are partially measuring the temperature of anode and internal glass surfaces, because the glass is partially transparant).
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Old 11th March 2013, 12:22 PM   #8
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Well yes, thats the concerns we also had in doing those measurements. A main disadvantage is, that you can't look through the glass body and it isn't sure, what side of the glass you're seeing in the thermographs.

But beside this, the most interesting thing for me was, the heat in the top glass-system-holders while using the 6C33C/6C33C, as it were said, that this one is also thermal-improved over the 6C18C/6S18S. Looking at the dT around the holders let me conclude, that forced cooling should not be an issue at all. (cracking)
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