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Post by ryman150 on Jul 15, 2005 23:44:23 GMT -7
Well, I did it. I got me my FIRST Dr. Z. It's a Maz Jr. 18. very nice condition. Red with grey piping.
The guy who shipped it to me pulled the two main tubes out and wrapped them up so during shipping they wouldn't fall out. I stuck them back in, but it looks like there should be the metal locking tube covers that go over them.
He says it never had them. But why do all the other small tubes have them?
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Post by kaseri on Jul 16, 2005 4:03:37 GMT -7
I played/borrowed a Maz 18 jr. for a while & I don't remember seeing tube covers on the power tubes. On my 6545 all of the preamp tubes have some sort of cover/holder on them but the power tubes don't.
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Post by goodwillsteve on Jul 17, 2005 15:06:10 GMT -7
yeah theyre supposed to be there. both maz 18s ive owned had them and all the others ive seen/ played had them. powertubes dont have covers. ryman150 is talking about preamp tubes.
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Post by myles on Aug 5, 2005 8:41:14 GMT -7
In the GT tube amp book, latest revision (the big hard cover one) we give some hints about preamp tube shields and how these actually can change the tone in many amps.
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Post by bluzsteel on Aug 11, 2005 7:53:32 GMT -7
Myles, would you mind telling us briefly how tone changes with pre amp tube covers ,as my Maz is missing three covers and I haven't gotten around to replacing them
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Post by G'OlPeachPhan on Aug 11, 2005 11:06:14 GMT -7
I'd be interested too myles if you're willing to spill the beans. ;D
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Post by bluzsteel on Aug 14, 2005 21:00:24 GMT -7
I found this on another site
Premp Tube Shields Magnetized -------------------------------------------------------------------------------- " I noticed that the tube covers closest to the magnet of my Weber C12N are magnetized: they repel each other. Any potential problem with that?
Re: Premp Tube Shields Magnetized -------------------------------------------------------------------------------- Yes, magnetic fields can "steer" the electrons as they transit from cathode to plate, causing them to not necessarily go "directly" there as intended...
Re: Premp Tube Shields Magnetized -------------------------------------------------------------------------------- I've read a lot of discussions about speaker magnets in close proximity to vacuum tubes in guitar amplifiers and everyone [ well not everyone ] agrees there's no problem with it. Someone over at Ted's board ran the math and determined that as close as the tube elements are to each other, and as fast as the electrons were travelling, that it would take a lot more field than you find around a speaker to affect the beam.You are the first person to mention magnetized tube shields that I'm aware of. Most of the new issue shields are aluminum, but I think that's just for ease of manufacturing - not because of their non-magnetic properties. "
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Post by sparrowhawk (Bob) on Nov 8, 2005 10:16:28 GMT -7
Preamp tube covers can also influence the microphonic characteristics of the tube. I once had an amp that would squeal with the preamp tube cover on, took it off and it was fine. Keep in mind a certain degree of microphonics can be a good thing - makes the amp sound a bit deeper and "reverby". So yeah, the presence or absence of a preamp tube cover can indeed influence the tone of the amp.
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Post by billyguitar on Dec 25, 2005 16:53:10 GMT -7
I thought preamp tube shields were there to help block radio interference. I got in the habit years ago of leaving the covers off so the tubes would run cooler. I've never had any problem with leaving the covers off.
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Post by myles on Dec 26, 2005 10:10:36 GMT -7
Myles, would you mind telling us briefly how tone changes with pre amp tube covers ,as my Maz is missing three covers and I haven't gotten around to replacing them Tube covers are generally used for two things .... to shield the tubes from stray noise on noisy amps and to hold the tubes in place. In great amps (look at very high end audio amps as an example) there are no tube covers. On a number of Fender tolex era amps one may find that removing the tube shields improves the tone. The reason for this is electronically simple. The cathode of a tube emits electrons that want to fly to the plate as directly as possible. With a tube shield in place (which is grounded) and more negitive in potential than the electrons, the electron flow "bends" and does not strike the plate as directly. Removing the tube shields can help in many amps and will make no change in others. In some amps removing it can make the amp more noisy too. It is one of those "try it and see" things in life. If you want to see how stray electrons can mess things up, crank your amp and shine a flashlight onto the plate of a tube. You will generally be able to hear this. If you have an amp that is not designed all that well this is where the tube shields will help. You also want to consider the security aspect of holding the tube. Many amps today use very cheap sockets and preamp tube can literally fall out of the amp. Using a tube pin straightener can re-align the tube pins properly for better tension but cheap sockets are cheap sockets. Many PCB ampd have their cheaper sockets board mounted and this can make things worse too. On the Z amps you do not have this concern as it's sockets are the best out there. I have even had very high end amp builders ask me where Z gets his sockets a number of times. I tell them I do not know (I was told once but do not remember) and they should ask the Doc.
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