Those pre amp tube covers!!!!

5150loveeddie · Post by **5150loveeddie** » Fri Jan 21, 2005 3:29 pm

The springs in them compress and then they rattle on the glass. It makes a raspiness on top of the note. I would take them off!!

What do you guys think? Is it me or what???!!!

Guest · Post by **Guest** » Sat Jan 22, 2005 2:15 am

I believe there purpose is for shielding from emf ,radio frequencies etc.

Removing them could cause unwanted noise or even oscillation

5150loveeddie · Post by **5150loveeddie** » Sat Jan 22, 2005 10:55 am

Yeah I know all that BUT they do alter the tone!!!!!! Try it!!!
And if they do not create to much noise without them you should not use them. Noise pick up would mainly be hum only from trannies.

On technical side of things here what happens. Tubes shield have an adverse affect on the tone of most amps. Tube has an element called a "cathode"which gives off electrons. Electrons are attracted to a POSTIVE charge and repelled by a negative charge. The cathode is in the center of the tube element called the "plate". The plate has a POSITIVE charge which it uses to attract electrons. OK, so now we have a cathode flowing electrons to the positive plate and all is well. Then we install a tube shield that connects to the chassis which is NEGATIVE in relationship to the plate. Confused? So are the electrons that see this NEGATIVE charge past the POSITIVE plate. Also the plate and the tube shield form a small value capacitor. Try it!!! I rest my case. If your amp makes to much noise or do nasty trick on ya, do put them back!!!! In my case here it is great!!!!!

myker · Post by **myker** » Sun Jan 23, 2005 11:05 pm

i have to agree with that, if you dont need em' dont use em'. but i know that if you add a few gain mods you are gonna need em. but most stock marshalls can be run without them with no problem.
mike

rjgtr · Post by **rjgtr** » Sun Jan 23, 2005 11:09 pm

You can put felts in them to keep them from rattling. I have a couple Rivera amps with shields that have felts (like Cymbal felts) in them and they definitely stay tight.

Necrovore · Post by **Necrovore** » Mon Jan 24, 2005 9:03 am

rjgtr wrote:You can put felts in them to keep them from rattling. I have a couple Rivera amps with shields that have felts (like Cymbal felts) in them and they definitely stay tight.

He was talking about how the shield when it connects to the base creates an adverse magnetic effect on the preamp tubes which affect your tone.

rjgtr · Post by **rjgtr** » Mon Jan 24, 2005 9:55 am

Nec,

He also complains about how they rattle on the glass, which is mechanical. See the first post.

I have also heard that removing them improves high end. I haven't really tried it with that in mind. Plus, I wonder if that isn't a good change for a Marshall that already has a lot of high end.

Post by **VelvetGeorge** » Mon Jan 24, 2005 12:32 pm

In my experience, a microphonic tube will have a more dramtic affect than a rattling shield. But I'll try pulling them next time I have a noisy gain stage and see the result.

george