Preamp Tube Shields

[bluesky636]

I tried a search with no luck.

Why do Trainwrecks not use preamp tube shields? With all the gain on tap, wouldn't the preamp tubes be prone to picking up external noise? I have a problem with noise in my amps due to the high powered wireless router in my studio. A combination of tube shields and moving the router as far away as possible cured the problem.

[Hogy]

The shields affect the sound. Try it on a particularly good/detailed sounding Fender some time and see if you can hear the difference.

Ken felt it was very noticeable and preferred his amps without shields.


Hogy

[bluesky636]

Since most, if not all modern tube shields are aluminum, and non-magnetic, how could they affect the sound.

[Hogy]

Since most, if not all modern tube shields are aluminum, and non-magnetic, how could they affect the sound.

The shield is a conductor connected to ground. This results in a capacitance that slightly dampens treble. It basically removes a layer of harmonics.

You should try it. If you can't hear it, well, one thing less to obsess about.


Hogy

[redshark]

How about tube O-rings if you don't want your tube to vibrate? that must not alter the tone Hogy...or it does?

[Richie]

I agree with Ken and Hogy, you can hear a difference. Sometimes too it depends on the tube, some the shield may help cure vibration problems if it is a noisey tube, or a slight feedbacky ring sound. The ring dampners help keep the tubes from the rattling or feedback etc. Somewhere I read in one of the old tube books the shields were suppose to be black. And not the shiney type. The military type which are black, and some of the older type had fins inside to help disapate the heat,and also help any vibration problems.

But if you have a good tube and it doesn't have any microphonic problems, it will sound better with the shield off. Not a fan of combos,and would rather have the amp head off the cab or at least set on some foam. Some amps are made not to use a shield.

[bluesky636]

I'll give it a try without the shields.

I use the Eurotubes dampers on my combos, and my amp head sits on Aurelex foam on top of the speaker cab.

[img::]http://farm9.staticflickr.com/8560/8894 ... 6a0f_c.jpg[/img]

[Richie]

I'll give it a try without the shields.

I use the Eurotubes dampers on my combos, and my amp head sits on Aurelex foam on top of the speaker cab.

[img:800:430]http://farm9.staticflickr.com/8560/8894 ... 6a0f_c.jpg[/img]

Yep like that..

[Mark]

I have tried listen to my Champ with and without the shield on the pre amp tube and I couldn't hear a difference, I suspect the Champ doesn't have enough gain and stages for this effect to be noticeable.

The other thing to bear in mind is noise, if the shields reduce your noise levels significantly perhaps it is better to use them.

[Richie]

You can also look up most any of the tube data sheets that show the differences with or without shields used.

Link to many different tube brand data.

http://tubedata.milbert.com/sheets11.html

[bluesky636]

You can also look up most any of the tube data sheets that show the differences with or without shields used.

Link to many different tube brand data.

http://tubedata.milbert.com/sheets11.html

Seems like a trivial difference to me:

http://tubedata.milbert.com/sheets/093/1/12AX7A.pdf

[VacuumVoodoo]

You can also look up most any of the tube data sheets that show the differences with or without shields used.

Link to many different tube brand data.

http://tubedata.milbert.com/sheets11.html

Seems like a trivial difference to me:

http://tubedata.milbert.com/sheets/093/1/12AX7A.pdf

It is trivial unless you are genetically endowed with bat ears or have an otherwise imaginative hearing. The rest of us, non-mutants, take these differences into account when designing ultrasound sonars and other high frequency stuff.
On the other hand, color of tube shield has not only a (easily) computable but also (not so easily) measurable and (almost) audible effect on sound. Differently colored solid bodies radiate and absorb heat at different rates. Thus the temperature inside the tube will vary with color of the shield. It's also a well known fact that the speed (i.e. energy) of electrons leaving the cathode is dependent on temperature. Shield of different color will make electrons move with different speed from cathode to anode. This influences transient response and explains why same amplifier with all shiny silvery shields feels "faster and unforgiving" compared to one with black shields or no shields as these tubes run a lot cooler.
In case you wonder. Yes, I am sober. No, you can't quote this without permission. I claim both copyright and copyleft on this.

[bluesky636]

Well, I'll definitely be leaving the shields on the preamp tubes of my amps, particularly the Wrecking Ball. I left the shields on, fired up the amp and turned it up all the way. Hiss but no interference from the high power wireless router. Then I shut the amp down, removed the shields and fired her back up. I was greeted by the rapid "putt putt" sound that the router induces in the amps. It sounds like rapid motorboating. I put the shields back on and the noise went away.