Re: [Harp-L] amp question: what are tube shields for?

[Bob Blunn <bblunn@xxxxxxx>]

Hi David,The main purpose for the shields is heat dissipation.  They can also help to block RFI. (Radio Frequency Interference.)  So, while they may reduce hiss (white noise) somewhat, they shouldn't impact the tone. Shields won't help for microphonics.  Microphonics is due to a physical defect within the tube itself - ( A loose electrode that vibrates due to the loudspeaker vibration.)  Most (all?) production tubes are microphonic to a certain extent.  (There are probably specialized patented tubes out there that aren't?)   Eliminating the vibration to the tube itself will reduce microphonics.   With separate head/speaker cabinet amps you can place the head somewhere other than on top of the speaker cabinet, But, with combo amps there's not much that can be done except to replace the offending tube.  I've seen RTV sponge-like contraptions meant to reduce tube vibration which could help, but I don't think the hi-temp RTV bands folks sell for this problem will have much impact in reducing tube vibration. Regards,Bob 
 
>[Harp-L] amp question: what are tube shields for? 
>Posted by: "David Brown" nonidesign@xxxxxxxxx 
>Thu Apr 24, 2008 1:49 pm (PDT) 
>Other than holding tubes in place and offering some protection from damage,>what function do tube shields serve? Do they have anything to do with>microphonics? Heat radiation/dispersion? Do they affect tone?>>Curious mind wanna know.>>Thanks in advance