markb
New Member
Posts: 29
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Post by markb on Jan 31, 2007 16:49:18 GMT -7
Is there any reason I need to use the aluminum tube sleeves on my Maz 38 preamp tubes? I get a harmonic vibration from them that I want to get rid of. Thanks,
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Post by Lefty on Jan 31, 2007 20:51:11 GMT -7
I doubt it the shields, more likely the tube. But basically they help hold the tubes in place, and keep out RF(supposedly) and maybe help with heat. Some say they can hear a difference with/without them. I figure if the Doc puts them on, there's a reason. Good enough for Leo and Doc, good enough for me.
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markb
New Member
Posts: 29
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Post by markb on Feb 1, 2007 7:08:06 GMT -7
Thanks for the feedback Lefty, I don't hear the vibration when the shields are off. I'll just hold onto to them in case RF becomes an issue or if they don't stay in place.
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Post by mudskipper on Feb 1, 2007 7:22:06 GMT -7
that's most likely the tube being microphonic and picking up various vibrations and such. i usually keep the shields off (especially on the first gain stage). there are clips you can use to hold the tubes down. they look like clips that are often used for EL84s. actually i bet they just cut those things down and used them for small 9 pin tubes. i haven't had any RF problems without the shields.
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Post by billyguitar on Feb 1, 2007 11:39:33 GMT -7
I've always taken them off, in all my amps. I've never had a tube fall out or heard any radio interference. One reason is I'm lazy the other is I think it would run a little cooler.
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Post by hdahs143 on Feb 2, 2007 7:14:42 GMT -7
Here's what Ken Fischer had to say about tube shields:
"Tube shields have an adverse affect on the tone of most amps. Here's the reason why. The tube has an element called a "cathode" which gives off electrons. Electrons are attracted to a positive 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.
To test this for yourself start with the tube shields off. That way you won't be dealing with hot tube shields later in this test. Warm up the amp and play, listening to the tone with a critical ear. Next put the tube shields back on. Be careful, the tube shields will be cool, but the tubes will be hot. Do not change any settings on the amp or guitar and listen to the tone again. I rest my case. If your amp makes too much noise or does nasty tricks with the tube shields off, do put them back on"
Just thought I'd pass this on.
Harold
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Post by mward on Feb 2, 2007 11:04:24 GMT -7
Except the tube shields are on the other side of an insulator (glass) so don't exist as far as the electrons are concerned. I think that theory is bunko, mang. Electrons aren't cats, they don't 'look' past the positive charge, see a negative charge, and then hide in your closet. :\
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SG123
Full Member
Posts: 221
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Post by SG123 on Feb 2, 2007 13:52:08 GMT -7
Yep, I think that's one for Mythbusters. Another thing going on is the extreme acceleration of electrons at close distances at high potentials - the thing that keeps tube performance from being affected by a strong speaker magnet right next to them. I am inclined to believe the capacitance effect though. Two conductors of opposite potential separated by an insulator..hmmm. "Electrons aren't cats". Some things are so true you just can't argue with them.
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Post by mward on Feb 2, 2007 19:44:39 GMT -7
I don't think the plate and the aluminum shield are close enough for it to be considered a capacitor. Usually the metal film has to be on either side of the glass with no gap and even then, glass capacitors are for very high voltages. I think we're safe on this one, although next time I have my amp apart, I will give it a listen and see. There are stranger things going on than that.
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SG123
Full Member
Posts: 221
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Post by SG123 on Feb 3, 2007 9:02:50 GMT -7
Not to muddy the water here, but the tube shields in many amps are made from steel. Lots of combinations to investigate.
I learned a long time ago that there are people who hear things I don't - and vice versa. Small things mean a lot to some, while others are happy if sound comes out of the speakers. Luckily, I'm somewhere in between - and happy.
I kinda like my highs rolled off a bit anyway.. Long cords, humbucker covers and tube shields don't bother me. [ hum and buzz are bigger problems, IMO ]
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Post by billyguitar on Feb 3, 2007 11:35:23 GMT -7
Even Z says he doesn't know as much about amps as Fischer did. I think I'll stand on his side of the line.
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herf
Junior Member
Posts: 80
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Post by herf on Mar 21, 2007 3:36:55 GMT -7
Even Z says he doesn't know as much about amps as Fischer did. I think I'll stand on his side of the line. That's the "appeal to authority" logical fallacy. Aluminum is nonmagnetic and separated by an insulator. I don't care if he's Einstein, he's wrong. Perhaps he was quoted out of context. Or was Fischer talking about steel sleeves? Even then...it seems unlikely.
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Post by billyguitar on Mar 21, 2007 8:10:11 GMT -7
Soundwise who knows? Whether Fischer was right or wrong would seem to be a futile debate. If there is a difference it has to be so subtle as to be meaningless, especially on a gig. I'll leave them off jus cuz I want to!
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Post by myles on Mar 21, 2007 11:06:05 GMT -7
If you look at most high end audio amps they do not have these shields. They are mostly there to keep the tube in the socket in amps that travel a lot.
In many amps you will actually hear a benefit (if the amp is properly built, wired, and shielded) when the tube cover is removed. Why? Because the shield is tied to ground and the electrons was to fly the most direct and straignt path from the cathode to the plate. There are positive voltages and neg voltages in a tube, and the plate is more positive than the cathode but the control grid is yet another potential with it's own part in the process too. Having a nice "ground" in the picture can cause the flow of electrons to travel a path less than direct.
In some amps removing the shields does nothing. In other amps you can hear a difference.
The differences when they are there are not all that subtle at times.
If you want to see how the plate of a tube can be easily influenced try working with a high gain circuit or a precise circuit such as a tube micprohone. Shine a common flashlight on the tube hitting the plate. You will hear it quite easily. I was in a studio once where a high end tube mic would go bonkers at a certain time each day. We thought it was electrical noise but it only happened with one particular mic. The mic had vent holes in it's body for the tube inside. At a certain time each day the sun in the window was at the right angle to hit the tube through the vent holes and wreak havoc. I was in a similar situation in South Florida when I was tech support for Control Data Corporation. During a particular month each year they had a problem that they could not pin down for years. All the 603 and 604 tape drives would drop all their tape into the tape loop boxes at the same time each day for two or three weeks. Look on a scope at the logic around the loop box and vacuum pump circuits. Found a "0" in the logic that should should have been a "1" (CDC 3800's were neg logic computers ... -5.8v = 0 and -1.1v was = 1).
Boy ... can I digress or what!!!!!!
Anyway ... sun coming in at the right angle got behind the tape enough on the side of the loop box, hit the sensor that said to the logic ... "more tape please" .... more tape spooled off the suply reel as the take reel was braked ... tape filled the box to the bottom where the vacuum intake was located ... plugged it .... vacuum motor was shut down by the fault logic.
So .... there is a little tip on not only amps but on the Control Data 603, 604, 606, 607, and BV series tape drives!
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Post by myles on Mar 21, 2007 11:07:53 GMT -7
If you look at most high end audio amps they do not have these shields. They are mostly there to keep the tube in the socket in amps that travel a lot. You can read the Ken Fischer info that was posted above ... I personally agree ... this is my take on it. In many amps you will actually hear a benefit (if the amp is properly built, wired, and shielded) when the tube cover is removed. Why? Because the shield is tied to ground and the electrons was to fly the most direct and straignt path from the cathode to the plate. There are positive voltages and neg voltages in a tube, and the plate is more positive than the cathode but the control grid is yet another potential with it's own part in the process too. Having a nice "ground" in the picture can cause the flow of electrons to travel a path less than direct. In some amps removing the shields does nothing. In other amps you can hear a difference. The differences when they are there are not all that subtle at times. If you want to see how the plate of a tube can be easily influenced try working with a high gain circuit or a precise circuit such as a tube micprohone. Shine a common flashlight on the tube hitting the plate. You will hear it quite easily. I was in a studio once where a high end tube mic would go bonkers at a certain time each day. We thought it was electrical noise but it only happened with one particular mic. The mic had vent holes in it's body for the tube inside. At a certain time each day the sun in the window was at the right angle to hit the tube through the vent holes and wreak havoc. I was in a similar situation in South Florida when I was tech support for Control Data Corporation. During a particular month each year they had a problem that they could not pin down for years. All the 603 and 604 tape drives would drop all their tape into the tape loop boxes at the same time each day for two or three weeks. Look on a scope at the logic around the loop box and vacuum pump circuits. Found a "0" in the logic that should should have been a "1" (CDC 3800's were neg logic computers ... -5.8v = 0 and -1.1v was = 1). Boy ... can I digress or what!!!!!! Anyway ... sun coming in at the right angle got behind the tape enough on the side of the loop box, hit the sensor that said to the logic ... "more tape please" .... more tape spooled off the suply reel as the take reel was braked ... tape filled the box to the bottom where the vacuum intake was located ... plugged it .... vacuum motor was shut down by the fault logic. So .... there is a little tip on not only amps but on the Control Data 603, 604, 606, 607, and BV series tape drives!
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Post by kruzty on Mar 21, 2007 11:19:22 GMT -7
It seems like you need to sleeve just to keep light off of the tube! ;D
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Post by billyguitar on Mar 21, 2007 13:15:00 GMT -7
Learn something new everyday! Thank you Mr. Wizard!
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Post by myles on Mar 22, 2007 10:33:04 GMT -7
It seems like you need to sleeve just to keep light off of the tube! ;D Actually that is only an issue in some sensitive tube mics
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Post by skydog958 on Mar 23, 2007 5:44:35 GMT -7
Myles, have you made the with/without tube shield comparison with any Z's? I know my SRZ came with three amp shields on the preamp tubes and my KT45 has one on the PI.
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Post by myles on Mar 23, 2007 8:25:39 GMT -7
Myles, have you made the with/without tube shield comparison with any Z's? I know my SRZ came with three amp shields on the preamp tubes and my KT45 has one on the PI. I leave the shields on my Z amps as they travel extensively. On the PI it would probably change nothing as this is a current driver and not a part of the gain stage.
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Post by nitehawk55 on Mar 23, 2007 8:41:06 GMT -7
I wonder if there are non metal shields made , perhaps bakelite or something of that type of material .?
Interesting theory on the electrons flowing to those shields but one thing for sure , electricity will find other paths to flow to if the conditions allow it , so it is logical ( in my best Spock voice ) ;D.
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Post by Lefty on Mar 23, 2007 9:06:48 GMT -7
I have both aluminum and steel shields, haven't noticed any difference between the two. But I would imagine the steel would be a better conductor/insulator. Personally I don't worry about it. It's all PnP. See my avatar quote.
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Post by mward on Mar 23, 2007 9:58:23 GMT -7
I'll stick a tube shield on the ef86 in my route66 and see if it makes a difference. Color me skeptical-spock.
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Post by nitehawk55 on Mar 23, 2007 14:02:54 GMT -7
I saw Spock on a TV show just recently , man he is looking old unlike Captain Kirk who's like the damn energizer bunny....keeps going and going and...........
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Post by Dana {aka gp} on Apr 3, 2007 9:29:54 GMT -7
Most of the shields in my amps have been removed simply because I didn't bother to put them back after swapping tubes. I also don't mind the idea that they might stay a bit cooler (and last longer) if they're allowed to run naked.
That said, I do have an ancient 12AX7 with long black plates (labeled 'United Radio' but I think it was RCA-made) that was slightly microphonic in V1 but settled right down when I put the spring-loaded tube shield over it.
Cheers,
-Dana
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