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previous: dale ray,your comments m... -- 4/20/2000 5:11 PM

Re: Swapping Preamp Tubes

4/20/2000 6:47 PM
Ray Ivers	Re: Swapping Preamp Tubes Dale, The good news is that it's usually pretty easy to optimize for the new tube type, especially if the correct value (perhaps I should say 'the range of correct new values') of cathode resistor required is less than the existing one, which would generally be the case if you were going from a 12AX7 to a 12AT7/12AU7 (more current required, less bias voltage needed, smaller resistor value). This way, you could easily just plug in the new tube, clip-lead the new resistor that in parallel with the existing resistor would result in the desired total cathode resistance and bias voltage, and try out the sound; if you didn't like it, no harm no foul - just unclip and you're back again. I use the TubeCAD program to find the values and model the circuit, and it's never let me down yet. If I can ever help you out to find a new resistor value, let me know. Ray

4/20/2000 6:47 PM

Ray Ivers

Re: Swapping Preamp Tubes

Dale,

The good news is that it's usually pretty easy to optimize for the new tube type, especially if the correct value (perhaps I should say 'the range of correct new values') of cathode resistor required is less than the existing one, which would generally be the case if you were going from a 12AX7 to a 12AT7/12AU7 (more current required, less bias voltage needed, smaller resistor value). This way, you could easily just plug in the new tube, clip-lead the new resistor that in parallel with the existing resistor would result in the desired total cathode resistance and bias voltage, and try out the sound; if you didn't like it, no harm no foul - just unclip and you're back again.

I use the TubeCAD program to find the values and model the circuit, and it's never let me down yet. If I can ever help you out to find a new resistor value, let me know.

Ray