Re: [Harp-L] amp question: what are tube shields for?
- To: "Bob Blunn" <bblunn@xxxxxxx>
- Subject: Re: [Harp-L] amp question: what are tube shields for?
- From: "David Brown" <nonidesign@xxxxxxxxx>
- Date: Sun, 27 Apr 2008 23:55:17 -0500
- Cc: harp-l@xxxxxxxxxx
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Thanks Bob,
I thought a connection to microphonics (if any) might have been to prevent
jarring loose electrodes that hadn't bee loose at manufacture.
Aiding in heat dissapation was my inital assumption, but finding the info on
line about their purpose was elusive.
THanks again
On Sun, Apr 27, 2008 at 4:01 PM, Bob Blunn <bblunn@xxxxxxx> wrote:
>
> 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_______________________________________________
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