Tube Shields?

Stew

The vacuum tubes in my Jolida JD100 have metal shields on them. I'm eagerly awaiting a nice pair of tubes and I'm hesitant to put the shields back on for fear of removing the labels. For those who have run tubes with
and without shields, do they make a difference?

Nightfall

Mine has very heavy metal shields that screw in and out, I run without them. @F1nut agreed that the tubes would run much cooler without them.

treitz3

Hello Stew and good afternoon to you. Dampers will be all you need in the Jolida. I haven't used the cages in many years.

Tom

Stew

Thanks to you both. Off with the shields! Nightfall, that's a beautiful glow you've got going there.

SCompRacer

Mil-spec IERC's are nice and functional. (International Electronic Research Corp). They actually reduce bare tube temps. They will snap onto the common tube shield base, though the bases are not necessary. More than what you want to know about them....

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

"An example from an IERC study in that article: 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. "

Here is a link to a research lab pdf page. Thank's to Aaron (ALL212). Takes a bit to load sometimes.

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

Shop wisely as some folks gouge. They come in various sizes.

Nightfall

@SCompRacer Do you know if operating temperature affects the performance/sound quality of a vacuum tube? Can you negatively affect sound quality by over cooling or over heating a vacuum tube?

SCompRacer

Heat affects tube life, and the military wanted something to improve tube life.

IMO, purity of materials, proper voltage and mA supplying the tube has more of an effect on sound quality than keeping the radiating surface of tube a hundred or so degrees cooler.

For instance, a thoriated filament is heated white-hot, about 2400 degrees Celsius. The thorium moves to the outer surface of it and emits electrons. An oxide-coated cathode gets orange-hot, about 1000 degrees Celsius and it emits electrons.

Some manufacturers reduce voltage up to 20% to extend tube life while allowing sufficient cathode temps to properly slough electrons. I would think a good designer would not lower voltage enough to sacrifice SQ.

Mhardy knows more than I do about tubes and hopefully he will weigh in.

Stew

Are these mainly for power tubes or for small signal tubes as well?

mhardy6647

Shields are important, sometimes essential, for high-gain circuits (magnetic tape head and phono preamp stages) -- they are far less necessary in line-level applications. In vintage equipment, the designers put shields where they were needed and left them off where not needed.

Modern equipment -- who knows?

treitz3

We are talking about the Jolida JD100. Nothing else....

Tom

txcoastal1

treitz3 wrote: »

We are talking about the Jolida JD100. Nothing else....

Tom

Catch up Tom...getting into tubes in general

treitz3

I was talking about the OP's general inquiry.

A discussion about tubes in general is a completely different discussion. Much like a discussion on the size of my Mom's posterior........which *could* be up for debate, depending on the angle.

Tom

treitz3

Nightfall wrote: »

@SCompRacer Do you know if operating temperature affects the performance/sound quality of a vacuum tube? Can you negatively affect sound quality by over cooling or over heating a vacuum tube?

Absolutely. Absolutely on both....with many factors riding on the tube/design/efficiency/current of said component.

It Depends on a myriad of factors.

Tom

Stew

OP's good with getting my learn on about tubes in general.

mhardy6647

In terms of the titular JoLida: if the shields are on small signal tubes -- voltage amplifier (driver) or phase splitters for the push-pull output stage (if it is a PP amplifier) -- the shields are, I'd opine, of questionable value. These tubes are usually relatively immune to picking up interference. There can be issues with microphonics (sensitivity of the tube's innards to vibration) but normal metal shields don't really help with that.

Easy to test tubes for microphonics. Tap the small signal tubes with a Tinkertoy or chopstick and listen for "interesting" (maybe loud) sounds from the loudspeakers -- or just shout at your tubes and listen for your own amplified (likely distorted) voice at the loudspeakers

The plate dissipation of small signal tubes (e.g., the near-ubiquitous 6922/12AX7/12AU7/12AT7 etc. 9-pin miniature twin-triodes) is pretty low; these tubes don't get hot (by which I mean "really hot") in normal use. Power output tubes get really hot -- and they're designed to take the heat, too.

This being said, well-designed amplifiers are either carefully designed for effective cooling of the tubes (particularly, that is, the outputs and HV rectifier, if so equipped) by convection or, in some cases, using a "boxer"/"muffin" fan.

Don't get me wrong, heat "is" the enemy -- but tubes were designed to function at fairly high temperatures. Look at the ratings on HV rectifiers or power output tubes -- operating temperatures of up to 200 degrees C are often spec'd as OK. That is oven temperature (392 degrees F).

Heck, in the 1950s, companies like Bendix made tubes for use in guided missles Those tubes are pretty darned rugged. They're also, amusingly, in pretty high demand for hifi nowadays -- even though many of them don't really sound any better than good quality "receiving tubes" for consumer use. The are tough, non-microphonic, and cool looking, though.

These aren't real "missle tubes", but they're still pretty rugged industrial versions of the 6SN7 (and sound pretty good, too).

Westies closeup by Mark Hardy, on Flickr




Sorry -- I got going again, didn't I?

mhardy6647

Oh, and (as Lt. Columbo used to say) one more thing.



If the OP doesn't have any "receiving tube manuals", he should, I'd opine

Pete Millett (who does this stuff for a living) has scanned and uploaded a plethora of tube docs to his wonderful website, http://www.tubebooks.org/index.html

Tube docs and data here:
http://www.tubebooks.org/tube_data.htm

If you're looking for one to start with, how about this one?
This has most of the favorite hifi tubes of yesterday and today in it... start here and then... collect 'em all!

http://www.tubebooks.org/tubedata/RC-21.pdf

mhardy6647

D'oh... a JoLida JD-100 is a CD player
Sorry.

I think the shields are there for a good reason; lots of nasty RFI hash flying around inside a digital component.

I mean, if you guys, empirically, find no audible difference sans or avec shields -- so be it. I am surprised, though, if that's the case!

heiney9

Just throwing this out there. My dac has a single tube sticking out the back side (still recessed) and it comes with your standard tube shield. Nothing special by any means. I run with it off because most owners state there is a positive difference in sound without it. I can't say that I actually notice. This tube is fairly isolated from the digital circuitry, so I don't worry too much about it.

It's a PITA to get off so I leave it off, but I don't really roll tubes in the dac anymore as found the one that works best since I have 8 tubes in the pre. I'd drive myself batty trying tube combo's in everything.

Just my .02c

H9

P.s. maybe do an internet search on your unit and see what other owners are saying.

mhardy6647

If there were a difference sans vs. avec the shields, I would think it would be in low level (background) noise. The problem (if there is one) isn't likely to be from the quality of electrical 'isolation from the digital circuitry' but rather the (potential) propensity of a tube's guts to act as an antenna, and "receive" RFI from the innards of the player.


source: http://www.6moons.com/audioreviews/jolida/jd100.html

It does look like whoever designed the player went to some lengths to 'shield' the digital from the analog (some big hunks of metal in between); perhaps the shields represent a "belt and suspenders" approach to isolation.

All of this being said, one cannot beat empiricism. It will do no harm to run without shields, so it's worth a try.

ALL212

I think we've got two reasons for tube shields.

1) Heat dissipation.
2) electrical shielding.

Part of the IERC document is that they found shields that are silver colored actually pushed the heat back into the tube and caused a rise in temperature. As stated before, heat is the enemy of tubes. They are rated for crazy hot temps but will last longer (per the document) if you can drop that temp even 10%.

If the shield is black on the inside/outside it will draw the heat away from the tube.

Hold on - Aaron logic coming up...please place your tray tables in the upright, locked position and fasten your seat belts.

If you have shields and they are silver you might do better to replace them with black ones - especially black on the interior.

That article about what they found during testing is very interesting.

Aaron logic complete, you are free to walk about the cabin.

SCompRacer

Per Doc' Schmale of Bottlehead fame...basically a repeat of what the linkage says. I respect Doc's gear and his factual opinion about the IERC's.

"I have decided to share some of my special stash of IERC tube shields with anyone who orders a Reduction phono preamp kit in February. As long as my supply holds out, Reduction kits will ship with IERC tube shields rather than the stock bayonet style shields. Long out of production, IERC shields were the most technically sophisticated tube shields made.

While regular bayonet style tube shields do the job in terms of blocking interference, they also slightly increase a tube's envelope temperature - by maybe 5% - and that can shorten tube life by about the same percentage.

When IERC introduced their shields they had an independent lab test them and found that they not only shielded RFI just as well as other shields, they actually reduced envelope temperature by 10% and more with the corresponding increase in tube life. The corrugated inner sleeve that transfers the heat also seems to have a slight damping effect that can help quiet microphonic tubes.

And they also look cool. "

They don't hurt SQ in my application, so I'll run with IERC shields up. And, like Doc says, they look kewl.

Stew

What's a good source for IERC shields? Or I could paint the ones I have with high temperature black paint - but where would I find some??

SCompRacer

I used some repurposed missile tubes in my Modwright gear.

A 6900 (5687 on steroids) used in ICBM warheads. Max altitude 80,000 feet, 500G impact load, 50G vibration acceleration. It's job, to survive until target reached and detonated. In audio applications, near twice the transconductance of a 5687. Incredible detail and dynamics.

Norm and I purchased MU 6900's. MU bought out the famous Bendix Redbank division and rebranded existing stock of tubes and continued production on Bendix tooling. It was a great way to get the tube for less $$ (often half or more compared to Bendix) until folks caught on and boosted the price to near or at Bendix branded pricing.

mhardy6647

-- fortunately we rarely exceed 75,000 feet

PS although I had to look 'em up those IERC shields are indeed very nice. Just needed to have my memory jogged.

Nightfall

I've always wanted to try a Bendix 5992 (I think that's right) in my 6V6 slot but the prices even on untested musty looking ones is crazy. I think about how I could pay for Tidal for several months or get a handful of records instead.

mhardy6647

Nightfall wrote: »

I've always wanted to try a Bendix 5992 (I think that's right) in my 6V6 slot but the prices even on untested musty looking ones is crazy. I think about how I could pay for Tidal for several months or get a handful of records instead.

I'll look through the plinker (pulls) boxes next week -- one never knows what's lurking in there

mhardy6647

Stew wrote: »

What's a good source for IERC shields? Or I could paint the ones I have with high temperature black paint - but where would I find some??

ahh, there's the rub.

SCompRacer

Stew wrote: »

What's a good source for IERC shields?

ebay, but some sellers gouge, some are fair priced. Surplus stores. Ideally you'd like to have a picture of condition versus a vague description. If's it's visible I don't think you'd want a scarred up, dented shield. Use that link I posted earlier for shield/tube size.

Unsure about the paint thing, maybe google to see if someone has done it.

Just a quick google found this surplus site. No affil, never dealt with them, list $2.50 to $5 each depending on tube size. Ebay nice condition similar pricing, some $10 each sellers. Lots of bulk sellers, like 20 or more shields (group buy?). Some free shipping at higher price, lower price they nick you 3 bucks or so for shipping. I'd prefer to have mine shipped in a box versus envelope, just to prevent smashing them.

https://www.surplussales.com/Tubes-Sock-Acc/TubeShields-1.html

Stew

Thanks. Will look on ebay. Just kidding on black paint.

mhardy6647

Stew wrote: »

Thanks. Will look on ebay. Just kidding on black paint.

It's a hot button topic, as you probably know

erniejade

When I had the Jolida ( great sounding player) I tried it both ways shield on and off running EI gold pins. At the time I had carver amazing and SDA1.2's and I could not tell the difference on or off. I also had my unit covers surrounded by dynamat so I am not sure if that helped with some vibrations or not being able to hear the difference?