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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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In Reply to: Re: driving kt88 triode PP with 1660S posted by drcy on December 13, 2004 at 20:07:18:
Cy,It's simple, really. I use an operating point for the input triode that gives a relatively low plate voltage, then couple the plate of that tube directly to the grid of the driver (second) triode. This necessitates a fairly large cathode resistor value (and resistor wattage rating) for the driver triode, because its cathode must sit off of ground the sum of the first triode plate voltage plus its own cathode bias voltage. This resistor value is calculated by taking the sum of these voltages and dividing by the driver triode bias current. This cathode resistor must be bypassed with a capacitor.
The use of a plate load (interstage) transformer for the driver triode offsets the power supply voltage problem that might result from the high cathode voltage if a plate load resistor were used, because the DC voltage drop across the primary winding of the interstage transformer is pretty small by comparison.
By these means you have accomplished a few worthwhile goals. You have eliminated coupling capacitors in the signal path (although there is still a cathode bypass capacitor), you have minimized the number of transformers (cost and electrical performance benefits, although not transformer dealer benefits, ;=((), and you may well end up with a great sounding amp if you make the right choices and compromises with respect to tube choices and bias points.
My only reservation with the 6EM7 is the high mu triode, which is much like a 5751. I've typically used lower mu, lower Rp tubes in the first triode location, so I don't know how well this will work. However, neither does either of us until one of us tries it!!
Have fun!
Kevin Carter
K&K Audio
www.kandkaudio.com
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- Re: driving kt88 triode PP with 1660S - KevinC 04:48:30 12/15/04 (0)
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