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Old 16th August 2005, 08:30 AM   #1
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Default Very powerfull push/pull circuit

I had this amp for a while in this form, and it had to be the most dymanic tube amp I've heard, and it's bass was extremly tight and powerfull, check out the feed forward from the anodes to the input of the output tubes, also the congugate filter on the primary of the output transformer.

Input tubes were 12ax's
Driver tubes were 12au's
Output tubes were Kt90's

It had a s..t load of feedback, on the scope it behaved like a big Threshold trany amp, flat out to 100k and down to 5hz, perfect 20k square waves and just the slightest ringing and quick settling when shunted with a 1uf cap across and 8ohm resistor at 20k square wave.
I soon grew tired of it as it was not too musical more like listening to a big Theshold or big Levinson, or Rowland.
So out went all the bells and whistles and the kitchen sink. (tones of feedback, congugate filter and the feedforward arangement) then it got musical, but i did miss all the dynamics and rock like bass.
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Old 17th August 2005, 10:11 AM   #2
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Interesting to see Mu-followers used as drivers like this. A pity the values of components are too small to read (e.g. the local feedback resistors around the OP stage) but it seems to be a workmanlike design.
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Old 17th August 2005, 12:20 PM   #3
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I remember the value of that resistor in the local (i called it feed forward) around the output stage was either 200k or 300k.
And the global feed back was 4.3k from the output transformer with 250pf across it, and a 100ohm to ground.

Cheers George
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