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Post subject: Balanced V3 tube
Posted: Wed Feb 05, 2014 7:33 pm
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Is it important to have the PI tube in V3 balanced? Amp is my US Blues Deluxe. In my tube swapping mode, I replaced the 12AX7 that came with the amp for a 12AT7 that was not balanced. Amp sounds great when I am noodling around, not so much in rehearsals. Perhaps a little knowledge is a dangerous thing.

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Post subject: Re: Balanced V3 tube
Posted: Wed Feb 05, 2014 7:39 pm
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For long-tailed phase inverter with a balance input to the stage, a balanced (between the duo-triode) MAY help. To be honest, very few tubes equally wear out their two triodes. So, after a few months of use, you would need to test the tube to see if the two-halves were still balanced.

So, how effective the extra cost to buy a balanced duo-triode? Dunno.


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Post subject: Re: Balanced V3 tube
Posted: Wed Feb 05, 2014 7:47 pm
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Yes, there seem to be mixed reviews here. Depends on the specific amp perhaps?

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Post subject: Re: Balanced V3 tube
Posted: Wed Feb 05, 2014 8:36 pm
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If you look at the phase inverter of the Blues Deluxe, you'll note that the two triodes are not equally loaded. Either by the anode plate voltage (one-half is in a voltage divide --- power/signal --- network) or the input signal onto the grids. This is prolly done to compensate for earlier stage(s) topology and/or a resultant non-symmetric stage = "on-purpose" non-symmetric output signal.

Plus, local feedback appears to be applied to one-half of the triode (and thus, one-half of the signal sine wave). So, I would guess that only half of the signal has local constraints. This half also appears to have all of the global feedback applied to it.

Now, a tube that tests with the two strong and near balanced triodes may sound better --- not only because of the amp's design --- but, also simply due to strong & quiet output. You need to try out the specific tube and see if it makes a difference.


http://www.webphix.com/schematic%20heav ... deluxe.pdf


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Post subject: Re: Balanced V3 tube
Posted: Fri Feb 14, 2014 10:55 am
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