Amp gurus...do preamp tube covers change an amps sound/tone?

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Gooseman

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To me, I use the eq, cab, speakers, guitar, pups, strings, tunings, pedals, and style to get my tone. I may switch out tubes and experiment with tubes, but I don't go taking off things that the amp was designed to have incorporated in it.

Really, you're taking off preamp tube covers to tweak your sound? I'm shocked and interested at the same time ...

:checkthisout:
 
it affects electron flow from cathode to plate in reference to grid to cathode voltage difference depending on impedance and bias. - hotter the tubes run, the easier for electrons to flow. not hard to understand and the reason you have heater filaments in your tubes to begin with - otherwise no electrons would flow and/or the electron flow would be poor until the tube was self heating itself with induced current from a source on the grid.

this is one reason why amplifiers do change sounds slightly when kept on for long periods of time - not mentioning thermal properties of capacitors and/or resistors.
 
I'm sorry, I don't buy into it. Preamp tubes rarely run hot enough for tube shields to make a difference. If the shields are solid, MAYBE, but all the covers I've seen utilize a hole in the top. That just comes off as pure corksniffing to me. I would be interested to read any documentation on this, though.
 
I have heard this before. I also have heard guys swear that their marshall sounds better with the rear panel taken off, something about the amp running cooler and breathing better. Probably why so many old jmp and jcm's are missing the back panel!!
 
I could maybe see that, because we're talking power tubes, which dissipate a lot of heat.

But preamp tubes?

gary-coleman.jpg
 
heater current at 6.3V *.3A per tube with triodes connected in series is ~1.89W - not enough to make a drastic difference as far as heat is concerned. the original intent of the metal casings is RF/EM interference - hence Jerry's reason in the other thread about putting the cover back on jake's 5150 as a possible solution.

however, this is to show that it wont cause a tube to overheat. this does not mean that it will not have any effects on sound. being as electron flow is what matters here in this variable i can guarantee it will make a difference. how much you or your other gear (cables, room, speaker dB thresh-holds, etc.) play as much of a part in being able to reproduce the differences is a whole different topic.

another example - stand outside in your underwear in the sun. then do the same thing with a blanket around you. tell me there is not a difference related to the time that you stand there?

cause damage to the tube? not likely. will it affect the tone? you need to remember tubes are a vaccum - voidless of all air as long as the barium is a mercury colour. to say it does not make a difference is to say the cloth of your guitar cabinet does not make a difference. just because you cannot hear a difference does not mean others can, have, or will.

in this topic the literal meaning of this acronym is to be mentioned:

YMMV.
 
I don't know whether it is in my head or not but last time you mentioned this on a thread-I tried it. I can definitely hear a difference :dunno:
 
glpg80":37508zdg said:
heater current at 6.3V *.3A per tube with triodes connected in series is ~1.89W - not enough to make a drastic difference as far as heat is concerned. the original intent of the metal casings is RF/EM interference - hence Jerry's reason in the other thread about putting the cover back on jake's 5150 as a possible solution.

however, this is to show that it wont cause a tube to overheat. this does not mean that it will not have any effects on sound. being as electron flow is what matters here in this variable i can guarantee it will make a difference. how much you or your other gear (cables, room, speaker dB thresh-holds, etc.) play as much of a part in being able to reproduce the differences is a whole different topic.

another example - stand outside in your underwear in the sun. then do the same thing with a blanket around you. tell me there is not a difference related to the time that you stand there?

cause damage to the tube? not likely. will it affect the tone? you need to remember tubes are a vaccum - voidless of all air as long as the barium is a mercury colour. to say it does not make a difference is to say the cloth of your guitar cabinet does not make a difference. just because you cannot hear a difference does not mean others can, have, or will.

in this topic the literal meaning of this acronym is to be mentioned:

YMMV.
Click to expand...

I want to say I appreciate your effort to quantify the difference with scientific fact, instead of some people who chalk differences up to "mojo" or whatever.

Thanks. :thumbsup:
 
I took my covers off because I like to see the glow of the tubes. If it sounds better :thumbsup: .
 
to be brutally honest i expected a flame suite to ensew from that post, not a thanks :lol: :LOL:

the only way i can put it is that there are too many variables to control here - these amplifiers are pure analog from the AC input of the primary's of the transformers to the room the speakers and the amplifier are sitting in. the world we live in is pure analog - you cannot tell me when you make an analog change to an analog variable component that nothing will come from the difference of the two when energy and time are involved. it might be a minute' difference, but its indeed there :)
 
I don't think the difference is perceivable in any condition but a solo, recorded environment. I certainly wouldn't bank on hearing the difference in a live situation.

But I am open to the possibility of a perceivable difference, I'm just very much in a crossed-arms state about it until I hear evidence of it.

I don't think every single change to an amplifier causes an audible difference. For instance, I upgraded the rectifier diodes in my DSL to UF4007's for shits and giggles, and it made no perceivable difference whatsoever. Complete waste of time. But who knows? If I had a higher quality OT, i might have been able to hear a difference. To that end, it would be a HUGE change to be able to hear a small change. I don't think switching a mallory capacitor in the preamp for a Sozo of the same value would ellicit any perceivable difference. Certainly, given that this is not a perfect world and that two capacitors may behave differently in the same role of a circuit, I don't think that difference is always audible in the narrow 82hz-4khz (roughly) spectrum that the electric guitar produces.

That's just my view on it. :dunno:

That being said, if someone perceives a difference, whether it's actual or in their head, they own the amp, and the difference is going to be more apparent to them than anyone else, so I guess that's what counts in most situations.
 
I wonder why I have a box of tube shields on my shelf........ :)
 
Well, a 12AT7 is only weaker than a 12AX7 in terms of gain. In terms of transconductance (how much input voltage is required for a given output current), it is rated for literally 10x what the 12AX7 is rated for. That is downright astonishing.

If you perceive a difference, awesome, but I've left the shield off numerous preamp tubes in various models, and had them on as well, and never noticed any difference.
 
I hear the most effect on the top end, it's like adding extra capacitance. Kind of like the difference between shielded and plain wire. They can also help transmit vibrations into a tube that is on the edge and make it squeal. I prefer not to use them. It's one of those things that you will never get a concrete answer on and you'll probably get plenty of hard asses swearing that it makes no difference at all. You can hear it and so can I, play your amp the way that you prefer, for those that can't......Okay, I believe you, carry on. It's kinda like those guys that swear metal film resistors sound just like carbon film only quieter. :bash:
 
I'm not sure but maybe one day I'll test it out and see if I can tell any difference... it wouldn't surprise me quite honestly, simply because with all the stuff flying around in the amp that I don't understand from an electronics stand point, I can't imagine that the shields block out a fair amount of interference. My amp actually came with out them and I ordered them to keep it quieter, I wasn't having any major noise issues but I don't use gates ever so I do everything I can to keep amps quiet.
 
They aren't truly necessary that I've ever seen. There are other measures in place in most amps to prevent pickup of RF. That nice little 68K resistor at the input of Marshalls is one measure. In some amps, shielded coaxial cable is used to connect the guitar input to the grid of the input stage The shielding is then referenced to chassis on one end and then terminated at the other, so it ends up using the chassis as a sort of shield for RF.
 
Nigel Tufnel":2p0itjrv said:
I hear the most effect on the top end, it's like adding extra capacitance. Kind of like the difference between shielded and plain wire. They can also help transmit vibrations into a tube that is on the edge and make it squeal. I prefer not to use them. It's one of those things that you will never get a concrete answer on and you'll probably get plenty of hard asses swearing that it makes no difference at all. You can hear it and so can I, play your amp the way that you prefer, for those that can't......Okay, I believe you, carry on. It's kinda like those guys that swear metal film resistors sound just like carbon film only quieter. :bash:
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Thats where I hear it as well. In the upper frequencies. Guys that use V30's won't hear any difference. It's plain as day in old Marshalls / Fenders.
 
Greazygeo":2talqv30 said:
Nigel Tufnel":2talqv30 said:
I hear the most effect on the top end, it's like adding extra capacitance. Kind of like the difference between shielded and plain wire. They can also help transmit vibrations into a tube that is on the edge and make it squeal. I prefer not to use them. It's one of those things that you will never get a concrete answer on and you'll probably get plenty of hard asses swearing that it makes no difference at all. You can hear it and so can I, play your amp the way that you prefer, for those that can't......Okay, I believe you, carry on. It's kinda like those guys that swear metal film resistors sound just like carbon film only quieter. :bash:
Click to expand...
Thats where I hear it as well. In the upper frequencies. Guys that use V30's won't hear any difference. It's plain as day in old Marshalls / Fenders.
Click to expand...
Yessir, I hear year and I hear IT. :thumbsup:
 
It makes a very noticeable difference in my Morris (more bite). I would never have believed this but I was told to try it by the builder. Then again, my amp is sensitive to every little change (picks, strings, woods, etc).
 
Nigel Tufnel":ztxbsloi said:
I hear the most effect on the top end, it's like adding extra capacitance. Kind of like the difference between shielded and plain wire. They can also help transmit vibrations into a tube that is on the edge and make it squeal. I prefer not to use them. It's one of those things that you will never get a concrete answer on and you'll probably get plenty of hard asses swearing that it makes no difference at all. You can hear it and so can I, play your amp the way that you prefer, for those that can't......Okay, I believe you, carry on. It's kinda like those guys that swear metal film resistors sound just like carbon film only quieter. :bash:
Click to expand...

So how do metal film resistors sound then? Full but tight low end, grindy midrange, with a slightly darker top end? :loco:
 
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