1X12 combo cabinet...tube rattle?

[yunger]

any reason this wouldn't work? the tubes are isolated from the speaker in a foil-tape lined space, vented to the outside.

[dan stanton]

Best thing I can tell you is take a compass and see how far away the magnet affects the compass. The magnetic lines can affect the tubes' electron flow. More than that, the back wall will be the "floppiest" section of the cabinet.

[Steve Conner]

I think proximity of the magnet is fairly a non-issue. I built this a couple of years ago:

http://scopeboy.com/scopeblog/wp-con...a-innards1.jpg

I checked bias current, etc. of all the tubes with the chassis in the cabinet and out, and couldn't measure any difference. I previously had a different speaker in it with an even bigger ceramic magnet.

Also, the tubes are on a kind of subchassis that's shock mounted on rubber bobbins, which is my answer to the tube rattle problem.

If you do go with your design, some holes in the bottom of the tube box to let cool air in might be a good idea, in addition to the hole in the back. At least under the power tubes, to get a kind of chimney effect going.

[yunger]

cool chassis steve. do you find that tube rattle is solely due to chassis vibration? if that's the case, my design does little more than increase surface area to possibly vibrate even more....in addition to the hot box created around the tubes.

[Steve Conner]

Well that's the thing, I don't know! The blast from the loudspeaker might rattle them too.

All I know is, I built this amp, have played it for a few years, gigged and recorded with it, and I haven't had any trouble with rattling tubes... yet.

Enzo used to sell a tube damper for the Peavey Classic 30, and maybe he has an opinion on this.

[yunger]

if it's vibrations transfered through the cabinet, i'll just isolate the entire chassis with rubber washers. i'd be curious to hear opinions on whether sound waves from the back of the speaker have much effect.