Measuring tube/component temperature

[Rob11966]

Hi all,

It is obviously important to design the layout of tubes and components to keep the operating temperature as low as possible and there are several threads on this.

I usually use the following tests (not anywhere near the HV stuff - I'm really talking about heat sinks for SS rectifiers, voltage regulators etc) -

If I can comfortably touch it its less than 50 degrees (Celsius)

If it's too hot to touch its over 60 degrees

If it burns when I touch, I shouldn't have touched it

If it smokes or smells, it doesn't matter what temperature it is - it's too hot!

A practical question; how do you measure temperature (if at all)?

Does anyone have any experience with infrared thermometer guns? They look like they could be very useful, particularly if they can be used on individual tubes and components at a distance.

Any thoughts?

Cheers,

Rob

[nigelwright7557]

I have a thermometer gun and it is useful if you work it right.

Mine has a laser on it for pointing but I noticed it is a little off target.
So I move the gun around a little to get the max tempertaure in the area of the device I am looking at.

[Ty_Bower]

I don't know if they've got a Harbor Fright in Australia, but maybe they ship international? They sell a couple inexpensive non-contact thermometers. I've got the little one, which I use to see if my tubes have cooled down enough for a restart.

Nicer one

Little one

[tomchr]

There are some non-contact (IR) thermometers around that plug into a standard multimeter (Fluke 80T-IR for example). There are also some thermocouple-to-multimeter converters around.

The IR ones work pretty well if you can aim them right. The thermocouple-based thermometers work well too but require good thermal contact between the thermocouple and the DUT, which may be a challenge at times.

~Tom

[boywonder]

I have used the pistol type IR thermometer guns, and they are very handy for non-contact temp measuring, although the surface characteristics can impact a good reading, ie reflectivity, absorptive characteristics, curvature, etc. Curved clear glass may be a little tough to get a good reading, although based on the other posts here it sounds like it works on tubes.

We also have a handful of little Omega engineering boxes that plug in to a std multimeter (two banana plugs) and accept a K-type thermocouple input. IIRC, the meter voltage reading is the temp reading in deg F or deg C depending in the switch setting on the omega box. MJ 3rd edition shows the thermocouple method with the thermocouple tied with wire around a tube. I would look on ebay for temperature monitoring stuff as this stuff is usually dirt cheap compared to buying it new.

[Rob11966]

Thanks folks,

I think that I will get a hand held IR thermometer of ebay. The only question is whether there is an appreciable difference between a $20 el-cheapo compared with a $100 fluke.

Cheers,

Rob

[TheGimp]

I use an Omega 'T' type thermocouple and calculate die temp from theta j-a and heat sink temp for solid state stuff.

Tubes are too hot to touch.

[Richard Ellis]

I've worked with the cheap IR guns & the hyper expensive versions($100+).
The nice guns are a joy to work with, the laser "finders" are a nice & functional touch, if a bit gimmicky. There is usually a diagram showing the area sense vs. distance as a small pictorial. EG. One foot range = 2" diameter sense pattern. After you use them for a while you will get a VERY good feel for what you are measuring.
The cheap guns just up & die.............usually the third or so time you will use it....you"ll change the batteries just to find out it is dead, no warning,....just dead!
The nice ones come in a nice padded case W/ Accessories, manuals etc.
Yeah, I like the expensive ones. Get what you pay for?? Perhaps. I liken it to a nice calculator....will last forever, if its' a good one. Had mine since 1985.

__________________________________________________ ___Rick..........

[TheGimp]

On the other hand, I seldom need to measure temp.

Design everything for a reasonable temp rise, control your ambient temp, and you won't need to measure it.

(1) Be sure to vent your chassis. Get the heat out. If you don't vent your chassis and trap heat in you will need to measure ambient INSIDE THE CHASSIS at full load to de-rate components.

(2) de-rate all resistors to 75% or less at your measured ambient temp. This gets back to item (1). The better you vent your chassis, the lower your ambient, the less you have to de-rate your components.

(3) Caps don't like elevated temps, especially Al-Electrolytics. Metal film tolerates temp rise better than dry slug and then wet slug tant, finally wet plate al is most sensitive.

Solid state devices will usually have Theta j-a specified in the data sheet. If you use LM317s as current sources, you should be able to calculate the temp rise for your specified heat sink, using power dissipation (bias current times grid bias).

Don't let your plates run red (watch them with the lights turned off).

[Rob11966]

Originally Posted by TheGimp

On the other hand, I seldom need to measure temp.

Design everything for a reasonable temp rise, control your ambient temp, and you won't need to measure it.

(1) Be sure to vent your chassis. Get the heat out. If you don't vent your chassis and trap heat in you will need to measure ambient INSIDE THE CHASSIS at full load to de-rate components.

(2) de-rate all resistors to 75% or less at your measured ambient temp. This gets back to item (1). The better you vent your chassis, the lower your ambient, the less you have to de-rate your components.

(3) Caps don't like elevated temps, especially Al-Electrolytics. Metal film tolerates temp rise better than dry slug and then wet slug tant, finally wet plate al is most sensitive.

Solid state devices will usually have Theta j-a specified in the data sheet. If you use LM317s as current sources, you should be able to calculate the temp rise for your specified heat sink, using power dissipation (bias current times grid bias).

Don't let your plates run red (watch them with the lights turned off).

Hi Gimp,

I do all of these things but being a perfectionist I would like to be able to confirm that my heat sinks are adequate. I would also be interested to see how hot some of my tubes get - particularly the 845's.

Hi Richard,

Yes, I am never happy with low quality gear. I was hoping that someone would write something exactly as you did so I could justify the extra expense of a good unit. I do love the fluke stuff and have have nothing but good service from my Fluke meter

Rob