Tube Dudes - Pay attention!!

ALL212

I use IERC tube shields on just about everything they will fit on. I did some reading/research a few years ago and they seemed like a good thing.

Yep - they're ugly.

As you might imagine it's a bit boring here in lockdown town and I decided to throw a different set of tubes at the Odyssey Audio pre. It uses a set of 12AU7's.

So cover off, grabbed the IERC shield and got reminded that tubes get warm! Used a cloth to pull the shields off and then...just for fun...touched the tube. Darn things were warm but easily removed with fingers.

And that's the way those things are supposed to work. I just never tested the theory. Cooler tubes should last longer and the EIRC shields definitely pull heat away from the glass. I tried the same thing on the Crack headphone amp multiple times and found the same result. The shield is HOT, the tube is NOT.

Faustin

Interesting. Thank you for the info.

muncybob

Is there a cross reference to match the tube to the shield?

ALL212

TR6-6015B fits standard 9 pin tubes 12a?7's, 6DJ8, EF86, 6C45pi, 6C32pi etc. well. If you have a taller 9 pin like the E80CC then use TRT6-6020B. I have one 112-2030-2nH that fits a 6080. Skinny but tall 7 pin tubes MS-24233-2. I used to have a link to a catalog of sorts that had these listed but I can't find it now.

None of the model numbers appear to determine whether this is the "finger" version or the flat plate version.

They are designed to lock also but most sockets don't have that option now. I have some sockets on Bottlehead products that use the much cheaper shiny shields and some of these do fit just over those sockets. I don't use any of the shiny shields anymore. Those were part of the military testing and were shown to reflect the heat right back into the tube.

pitdogg2

But you cannot see the atom smasher fire inside the tube....

SCompRacer

This is how it looked before I got totally irked.

ALL212

That is the drawback...

And for cheap tubes that you do want to see the atom smasher working- fogetaboutit...I like the light show!

But some of these tubes are pricey...

delkal

There is no way the tube shield can be hotter than the tube. Not physically possible. What you felt has more to do with thermal mass and conductivity. The shields look thick and metal so when you touch them there is a lot of heat in the shield to get transferred to your fingers. The tube is thin glass so even if it at the same temperature their is not as much heat to transfer.

But the shields do act as a heatsink and with the larger surface area should keep your tubes running a little cooler.

ALL212

You don't have any of these...nor have you tried it have you?

ALL212

muncybob wrote: »

Is there a cross reference to match the tube to the shield?

From an old Polk forum post:

https://forum.polkaudio.com/discussion/177718/tube-shields/p1

https://www.qsl.net/kh6grt/page4/shields/shields.htm

https://www.pearl-hifi.com/03_Prod_Serv/Coolers/PEARL_Tube_Coolers.pdf

ALL212

@delkal - I'm not "picking" on you per say in the following. But your comments triggered a thought and I think I had your same conclusion before reading and experiencing what I have.

"There is no way the tube shield can be hotter than the tube. Not physically possible."

I would argue that not only is it physically possible but it is a physical necessity.

Tubes get hot because they have a filament that is heated to release electrons. That heat has to be constant or the flow of electrons would not be stable and the tube would be worthless. The heat in the glass is nothing more than a by-product of that necessity and the temperature we measure from that glass is relative to the ambient air temperature around the tube. Cooling the glass (or not cooling it) has no effect on the filament unless the tube is exposed to extreme temperature variations.

"What you felt has more to do with thermal mass and conductivity. The shields look thick and metal so when you touch them there is a lot of heat in the shield to get transferred to your fingers."

I suspect if you measured the material in the tube shields (it is metal) you would find them much thinner than the glass in the tube. I've disassembled a few tubes (to clean them... ). It's not easy and the older the tube the harder and thicker the glass. That glass is much thicker than your standard incandescent light bulb of days gone by.

"The tube is thin glass so even if it at the same temperature their (there) is not as much heat to transfer."

As stated above the tube glass is thicker than the shield material.

Here we go... Arguments are welcome.

If the tube is exposed to an ambient air temperature that doesn't vary much the heat dissipated by the tube is constant. The articles posted above have references to studies done by the military that states the tube glass temperature is reduced by 20% to 25% (as high as 38%) if these shields are applied. The heat has left the glass. Where did it go? Ambient air temperature is assumed to not have changed. It only has one place to go and that's the material in the shield where it is then dissipated into the air.

So I would argue that the shield must be hotter than the glass of the tube unless it's one of those pretty shiny ones (see reference below in italics).

Fun reading from one of the articles:

"...a 6AQ5(6005) tube operating near maximum plate dissipation has a bare bulb temperature almost 460 degrees F. Enclosed in a bright JAN shield its bulb temperature rises to 600 degrees F. With an IERC type B cooler installed the bulb temperature drops to 365 degrees F. This is a 20% drop from its bare bulb temperature and an 39% drop from its JAN shield temperature. This related to a tube survival rate after 500 operating hours of 35% using no shield, to less than 5% using the JAN shield, to over 95% still working using the IERC type B cooler. In another example from a GE study: From a batch of 200 6AQ5(6005) tubes running at 502 degrees F, 15% were still operational after 2500 hours. A second batch running at 428 degrees F, 74 degrees cooler or about a 15% reduction in bulb temperature, still had 90% operational after 5000 hours. It seems "small decreases in bulb temperatures often result in seemingly disproportionately large increases in tube life". "

marvda1

small signal tubes don't put out that much heat and you be overdamping the sound of your amp. do listening tests with and without the shields/dampers.

ALL212

I agree that they don't put out as much heat as other tubes. However, they do get hot.

I'm not sure what you mean by overdamping. Would you clarify that?

This "argument" is not about the sound of a tube but rather the lifespan of a tube. But for the sake of the comment I have listened to naked tubes, tubes in shiny shields and tubes in flat black shields and have never heard any difference.

I suppose you could cool the glass tube to the point that it would affect the filament operation. That would not be good!

marvda1

taking away from the lively sound of an amp making it sound slow and a little dull.
I did this to my system when I placed isoacoustics iso pucks under all of my components and didn.t notice it until someone came over and said the system was dull sounding, we decided to take the iso pucks from under the equipment and lo and behold my system came to life.

ALL212

@marvda1
Interesting! I've not experienced that...

marvda1

have you compared the sound with and without?

ALL212

As stated above - yes. No difference in my systems.

mhardy6647

Most of the heat in (most) operating tubes comes from the plates -- that's where the juice is being dissipated.

Small signal tubes don't generate much heat as long as they're run within their normal operating conditions. Now, big power triodes or HV rectifiers are a different kettle of fish.

That said, let's look at a 12AU7.
http://www.tubebooks.org/tubedata/HB-3/Receiving_Tubes_Part_2/12AU7-A.PDF

The filament draws 1.9 watts
The plate dissipation (both triodes) is 5.5 watts
(and that is essentially the excess power that's not being invested in the tube's doing its job as two amplifier elements)

ALL212

Filament lives in the plates?

mhardy6647

Now, let's look at a "modern" (it's all relative) dual plate 2A3 power triode.
From RCA RC-17 (http://www.tubebooks.org/tubedata/RC17.pdf)



A single 2A3 can output about 3.5 watts of audio power under 'hifi' conditions (5% THD... don't start with me. )

in so doing, its filament (which is also its cathode) consumes 6.25 watts
and the plate dissipation is 15 watts

These bad boys get hot -- don't ask me how I know.

ALL212

Here's the junk on the 6AQ5 that the mil studies used. And I use them - on the Crack-a-2-a headphone amp as shunt voltage regulators. They do get toasty.

marvda1

reading up on your tube shields, they don't seem to claim any tube damping, that might be why you don't hear a difference. rings like herbies and silicon which are designed to damp tubes.

mhardy6647

ALL212 wrote: »

Here's the junk on the 6AQ5 that the mil studies used. And I use them - on the Crack-a-2-a headphone amp as shunt voltage regulators. They do get toasty.

Yup, a 6AQ5 will
It's essentially a 6V6 in an itty-bitty 7 pin miniature bottle -- which doesn't help its heat dissipation!

PS You can make a nice, cheap single-ended or push-pull hifi amp using 6AQ5s Just sayin'.

delkal

ALL212 wrote: »

Tubes get hot because they have a filament that is heated to release electrons. That heat has to be constant or the flow of electrons would not be stable and the tube would be worthless. The heat in the glass is nothing more than a by-product of that necessity and the temperature we measure from that glass is relative to the ambient air temperature around the tube. Cooling the glass (or not cooling it) has no effect on the filament unless the tube is exposed to extreme temperature variations.

I did some more thinking about this and I forgot about the electromagnetic radiation that can pass thru the glass (I was thinking only about conduction). So you are correct something outside the glass can be hotter (think your windshield and the dashboard in the summer).

But that raises another question. Normally infra red radiation passes thru glass and heats up the air around it and is dissipated. If you have a hotter metal piece attached to the glass wouldn't that make the internal temperature of the tube go up?

ALL212

@delkal
Good point - some of this is "magic" to me as well. And I don't have much beyond a fancy ****-o-ciate (I gotta spell it slowly...) degree from the local comm college - so we'll need a much smarter person that me to chime in on that!

@marvda1
Opinion time... The shields with the "fingers" in them should work as dampers. The fingers touch the glass on all sides. I'm just not sure how well since that aspect wasn't included in any tests.


The shields with the "plates" maybe not so well as there are gaps in the insert?


But that's all supposition - I don't use them for damping.

voltz

Hmmm. I have learn to trust Arron on many things... but....on these....

just kidding, thanks for the advise again!