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Old 31st October 2011, 02:32 AM   #111
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Quote:
Originally Posted by tinitus View Post
hmm, can you really feed a tube amp with a balanced signal without having a transformer at input, and not have grounding issues ?
Yes. I do it all the time.
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Old 31st October 2011, 04:03 AM   #112
tinitus is offline tinitus  Europe
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great

looking at 12BH7 I found this amp (attached)

is it a good tube ?

12BH7A-STR TAD Premium Selected (symmetrisch/balanced) - TAD Vorstufenröhren SELECTED

nice that TAD offers 'balanced matching'
they also suggest ecc81 as a good 'phase driver'
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Old 31st October 2011, 01:45 PM   #113
tinitus is offline tinitus  Europe
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right now studying these curcuits
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File Type: png 6MP17_CIRCLOTRON.png (40.4 KB, 167 views)
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Old 31st October 2011, 07:42 PM   #114
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Quote:
Originally Posted by tinitus View Post
great

looking at 12BH7 I found this amp (attached)

is it a good tube ?

12BH7A-STR TAD Premium Selected (symmetrisch/balanced) - TAD Vorstufenröhren SELECTED

nice that TAD offers 'balanced matching'
they also suggest ecc81 as a good 'phase driver'
The 12BH7 and 6CG7 are both good driver tubes, and are pretty much the same thing as a 6SN7 in a different package.

The ECC81 (12AT7) is nice because it gets good gain but does not have bandwidth problems like the 12AX7. You can put some current through it so it can be used as a driver tube too.
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Old 31st October 2011, 08:10 PM   #115
banat is offline banat  Serbia
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Here is one my idea and schematic for balanced input gain stage and driver stage , with full balanced signal input to input ecc81 tube , than DC connected to grids of bootstrapped differencial driver stage of ecc99 or 12bh7 tube .
Balanced corection negative feedback is conected to both cathodes of ecc81 input gain stage .
Of course that different value of pasive elements can be aplied to achieve different electrical and sonic parameters .

Best Regards !
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Old 31st October 2011, 11:57 PM   #116
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Quote:
Originally Posted by atmasphere View Post
The 12BH7 and 6CG7 are both good driver tubes, and are pretty much the same thing as a 6SN7 in a different package.

The ECC81 (12AT7) is nice because it gets good gain but does not have bandwidth problems like the 12AX7. You can put some current through it so it can be used as a driver tube too.
Just curious, what do you mean by "bandwidth problems?"
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Old 1st November 2011, 12:20 AM   #117
tinitus is offline tinitus  Europe
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looks great

any sense in using 2x ecc99, or 2x ecc81

or is the ecc81/ecc99 actually a good combination of smooth and neutral
but maybe it also depends on the choise of output tube, voltage and bias, etc etc
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Old 1st November 2011, 09:35 AM   #118
banat is offline banat  Serbia
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Well there is no general rules for small signal tubes type choice for this aplication

But yes miniature noval ecc81 placed at input gain stage in combination with noval ecc99 (12bh7 / 6cg7) for driver stage work fine .( ecc82 tube for input stage is OK to ).

Atmasphere have right ! 6sn7 tube is good pair for both input and driver stage ,than all Amps tube socket will be octal , or if you prefer many nice glowing octal tubes on the top plate on Amp chassis than four octal triode 6j5gt is OK to .

My few word about ``smooth`` and`` neutral`` tube Amp timbre :
OTL Amps sounds positive smooth but Not neutral ,god designed autotrafo coupled Circlotron Amp sounds prety close to that to .
`` neutral `` Amp sound I connect close with`` lifeless `` Amps sound music reproduction which usually we can hear from 99,99% of standard designed SEPP SS based Amps ,I think this negative sound effect apear since this SS Amps usually work with relative high aplied GNFB percent, to cure high open loop Amp distortion, there soundstage presentation is poor to .

Best Regards !
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Old 1st November 2011, 04:50 PM   #119
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if we should decide here and now, I would lean towards ecc82 with 12BH7(A), but not yet sure
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Old 1st November 2011, 04:54 PM   #120
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Originally Posted by SpreadSpectrum View Post
Just curious, what do you mean by "bandwidth problems?"
Open loop you are not going to get much over 12-15KHz out of a 12AX7- it is high impedance and so is affected by capacitance in the layout. To reproduce the audio passband without phase shift, you need bandwidth to 1/10th and 10X the cutoff frequencies. A 12AX7 won't make it to 100KHz or 200KHz but a 12AT7 will do it with with ease.
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