Tube covers - are they important?

[Steve Jones]

What purpose is served by clip on metal covers on vacuum tubes? are they just for shielding, and if so how effective are they? Do they cause heat buildup? I have some gear that is missing it's covers and am wondering if I should go try and find some.

 

[Guest]

As far as I know, they are just for shielding. They are effective in high gain tubes. One of my guitar amps gets some hash from a 12AX7 without the shield.

Heat is not too much of a problem since the shields act as descent dissipators.

 

[mcs]

[quote author="Steve Jones"]What purpose is served by clip on metal covers on vacuum tubes? are they just for shielding, and if so how effective are they?[/quote]
They are for shielding and very effective. In a tape playback amp I built I get a lot of hum without shields and zero with shields. If you don't have hum problems they are not needed. My phono preamp has unshielded tubes for instance without any problems.

Do they cause heat buildup?

YES! Unless they are heat dissipating types they do. The heat dissipating shields are normally black and have spring-loaded plates that "hold" the tube.

Best regards,

Mikkel C. Simonsen

 

[soundguy]

I get alot of RF with my altec 436 if I dont have the shields installed...

dave

 

[CJ]

They also hold the tube in place for road trips.

Some guitar amp freaks think that the shields harm the sound, so they remove them. Experiment.
Heat buildup is not a factor in most 9 pin bottles.
I do have a headphone amp where I heat sinked the tubes to the chassis, which is kind of weird! 5751'as or something like that.