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ART MPA gold tube swap question
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Gems Records
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#1
25th July 2009
Old 25th July 2009
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ART MPA gold tube swap question

Hello, fellow Gearslutz. I just got some NOS Motorola tubes, and am wondering if the metal caps surrounding the tubes are necessary to put back in? Pls help!! cheers
#2
26th July 2009
Old 26th July 2009
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Depends on what you mean by "necessary" - if you like extra noise then by all means leave them off.......
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26th July 2009
Old 26th July 2009
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They usually sap some of the high-frequency response so I recommend leaving them off so long as your tubes aren't picking up RF noise (which they usually won't). Try it both ways and see what works best for you.
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26th July 2009
Old 26th July 2009
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Quote:
Originally Posted by BOWIE View Post
They usually sap some of the high-frequency response so I recommend leaving them off so long as your tubes aren't picking up RF noise (which they usually won't). Try it both ways and see what works best for you.
Er, um, I beg your pardon?

RF shields sapping your high frequency response? No. That's like a green sharpie making your CDs sound better.

What they MIGHT do that perhaps you could interpret that way is that they might damp microphonic ringing in a marginally bad tube that, if it was very slight, might be misinterpreted as additional high end. You don't want microphonics in your tubes. It's not a good thing.
Gems Records
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26th July 2009
Old 26th July 2009
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Hello, again. The stock tubes in my MPA were horribly microphonic, which is why I wanted to replace them in the first place.

The metal shields certainly didn't prevent that.

Wouldn't their removal allow better heat dispersion?

My concern was that there are wires running disturbingly close to the tubes, and I would'nt want to harm them due to the heat.

Anyone know if it is harmful to the unit to remove them?

Also, I was under the impresion that RF sensitivity was a sign of a bad tube. Any thoughts?

cheers
James Iverson, producer
Gems Records | Great view, better sound.
#6
26th July 2009
Old 26th July 2009
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Quote:
Originally Posted by John Eppstein View Post
Er, um, I beg your pardon?

RF shields sapping your high frequency response? No. That's like a green sharpie making your CDs sound better.

What they MIGHT do that perhaps you could interpret that way is that they might damp microphonic ringing in a marginally bad tube that, if it was very slight, might be misinterpreted as additional high end. You don't want microphonics in your tubes. It's not a good thing.
Just to offer you some reading, I did a qick Google search and came up with several forum threads. Are all these people imagining this?
Tube Shields [Archive] - The Gear Page
Rig-Talk • View topic - Preamp tube shields making a difference in tone?
2 in one day! Those silver preamp tube shields ... [Archive] - The Gear Page
#7
26th July 2009
Old 26th July 2009
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Quote:
Originally Posted by Gems Records View Post
Wouldn't their removal allow better heat dispersion?

My concern was that there are wires running disturbingly close to the tubes, and I would'nt want to harm them due to the heat.

Anyone know if it is harmful to the unit to remove them?

Also, I was under the impresion that RF sensitivity was a sign of a bad tube. Any thoughts?
It's about equal w/ or w/o. The spring in the shield acts like a heat-sink which compensates for the lack of air-flow.

No, it's not harmful in that unit.

Sometimes, the wiring is an issue. I've seen gear that was sloppily put-together with wires touching the tubes, etc. Gently move them out of the way if you can.

RF sensitivity has more to do with design than a tube just being bad. Though, you are correct, some tubes will go bad and become sensitive to RF.
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26th July 2009
Old 26th July 2009
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#9
26th July 2009
Old 26th July 2009
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Great initial question! I was wondering about this...How about this, I'll try it, and post the results?

Here we go:
tlm103 into an ART MPA Gold with Siemens und Halske Valvo NOS tube. First read with the shield, second read without the shield. I'm a voice over guy, so to accomodate you rock gurus I read a sentence from a technical program and then sing it really badly with whack dynamics - blustery, high and screamo, and then up close and growly. Enjoy.

http://www.lanceblair.net/files/ARTMPAShieldTest.wav

BTW, the MPA settings are High Voltage, Input 1 o'clock, Impedance 3 o'clock, and Output 2 o'clock.

Now I need to get a green sharpie, although my clients say they loved my upgrade from red to black.
#10
27th July 2009
Old 27th July 2009
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LOL...thanks. Science In Chains, perhaps? I wanted to give you some different flavors in one short clip. I can't stand the "shootouts" here (and elsewhere) that involve someone droning on.

As for the sound...yeah, I hear more air too and less sibilance. I'm surprised. Everything was set the same and I measured my body positioning and axis and distance to the mic. If anything the tubes had slightly more time to warm up in the "covered" version which I did to make things more fair.

For me, the covers are staying off!
#11
6th August 2009
Old 6th August 2009
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hi, tried Tungsol 12AX7 in the MPA Gold and it was absolutley superb - these are just new Russian made cheap tubes and could not beleive how smooth and nice they sounded.
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