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Plate temperature measurement
Plate temperature measurement
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Old 2nd September 2019, 02:37 PM   #21
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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In the computations below, I believe you forgot to consider heater and screen dissipation, all of them constitutes part of the heat radiated from the envelope. Note that some tubes (In my design 6JN6's) runs very hot with the heater only powered.
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Old 2nd September 2019, 03:43 PM   #22
PRR is offline PRR  United States
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I was going to say what Osvaldo just added: there's 5.67W in heater, and maybe 2W in screen.

35+5.67+2W= 42.67 Watts full-hot 6L6GC

My IR thermometer work on a 6550 @ 39W Pdiss clearly showed max observed temperature "around" the plate and significantly lower temp at top and bottom.

A non-calibrated observation: I once burned my hand on a coke-bottle 6550. The 1st-degree burn was coke-bottle shape and worst around the plate area.

Tempilstik Temperature Indicating Sticks are the time-honored way to measure surface temperature without adding much thermal mass or insulation. Sadly each only indicates one temperature and they are not cheap enough for a DIY-er to have a "full set".
Tempilstik – markal.com
Fastenal link

Last edited by PRR; 2nd September 2019 at 03:48 PM.
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Old 2nd September 2019, 10:51 PM   #23
trobbins is offline trobbins  Australia
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If you have access to physically small thermocouples, and were keen enough, you could set up some jigs to see how much variation you get with each jig, and using the normal techniques like keeping the thermocouple wire on the glass for some distance to avoid thermal wicking.

That could be backed up by using thermal colour change patches, and by using the cheap thermal guns (again set up in a jig to maintain pointing and distance, and knowing the sensor's response).

All good fun if that is what you are interested in.

A practical output is to keep the glass clean, and heed the advise on anode orientation when locating valves beside each other (or others, as some quads and sextets can look decidedly cramped together and close to nearby vertical surfaces like transformer windings).
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Old 3rd September 2019, 10:39 AM   #24
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by Sorento View Post
from "Kohl 1960 Materials and Techniques for Electron Tubes"
This is sooo cool! Brilliant find, thank you!
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Old 3rd September 2019, 10:46 AM   #25
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by Osvaldo de Banfield View Post
In the computations below, I believe you forgot to consider heater and screen dissipation, all of them constitutes part of the heat radiated from the envelope. Note that some tubes (In my design 6JN6's) runs very hot with the heater only powered.
You are quite correct, I have indeed neglected that.

Let me do over: to stay with the same tube, a 6L6GC heater dissipates 5W and the heater roughly 6W, so we're looking at 41W at full power or maybe 27W at 40mA, which give respectively 212C (24W radiation and 17W convection) and 157C (15W/12W) average envelope temperature.
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Old 3rd September 2019, 10:49 AM   #26
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by PRR View Post
My IR thermometer work on a 6550 @ 39W Pdiss clearly showed max observed temperature "around" the plate and significantly lower temp at top and bottom.

A non-calibrated observation: I once burned my hand on a coke-bottle 6550. The 1st-degree burn was coke-bottle shape and worst around the plate area.
Yes, this is my memory of the reading from the FLIR as well. So much that I casually thought I was seeing through the glass (at the time I wasn't aware the IR absorption would be so pronounced). I have in the meantime gathered a few dustbin-grade tubes, I intend to cut the envelope open and run a few experiments over the weekend, I'll post some picture as soon as I have any.
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Old 3rd September 2019, 10:58 AM   #27
baudouin0 is offline baudouin0
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Think they get much hotter than 160 deg. The glass may stop your camera reading the correct result. If they glow a dull red then its about 500 degC, so maybe 400 degC.
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Old 3rd September 2019, 11:17 AM   #28
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by trobbins View Post
If you have access to physically small thermocouples, and were keen enough, you could set up some jigs to see how much variation you get with each jig, and using the normal techniques like keeping the thermocouple wire on the glass for some distance to avoid thermal wicking.

That could be backed up by using thermal colour change patches, and by using the cheap thermal guns (again set up in a jig to maintain pointing and distance, and knowing the sensor's response).

All good fun if that is what you are interested in.
Well this is the power of the white rabbit, isn't it... :-) (I do deal with radiative transport at work, so I have some affinity with this problem space)

I was wondering more on the side of what PRR was saying, to use a "sock" of thin diffuse material (piece of black cloth or paper?) fitting snugly the envelope to improve the reading ability of the IR thermometer.

Quote:
Originally Posted by trobbins View Post
A practical output is to keep the glass clean, and heed the advice on anode orientation when locating valves beside each other (or others, as some quads and sextets can look decidedly cramped together and close to nearby vertical surfaces like transformer windings).
Reading this made me think if we couldn't actually visualize the radiation spread of the tube, maybe heat it up and disperse some dust in the air (flour?) then quickly take a picture. Trying to create a form of Tyndall effect, you know, like this

Click the image to open in full size.

A quick look on the web seems to indicate acrylic could be a way to do this. Possibly there is enough irregularity in the material that holding it horizontally (you know, "edge on") next to the tube might reveal a cross section of the radiated field, like this:

Click the image to open in full size.
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Old 3rd September 2019, 11:21 AM   #29
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by baudouin0 View Post
Think they get much hotter than 160 deg. The glass may stop your camera reading the correct result. If they glow a dull red then its about 500 degC, so maybe 400 degC.
That's right. If the plate is running at 30W, plus 5ish screen plus 6ish heater, you're looking at 41W of radiation, which should be approximately 485C at the plate (and 212C at the envelope), both average temperatures, and both assuming my estimations of the sizes are accurate enough.
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Old 3rd September 2019, 11:24 AM   #30
pcbampmaker is offline pcbampmaker  New Zealand
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Quote:
Originally Posted by pcbampmaker View Post
Let me do over: to stay with the same tube, a 6L6GC heater dissipates 5W and the heater roughly 6W, ...
Bah. 5W *screen* of course, 6ish W heater. Or the more accurate numbers from PRR
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