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Re: Problem when large volume

Posted by sorenj07 (A) on April 11, 2007 at 19:38:13

In Reply to: Re: Problem when large volume posted by waterman on April 11, 2007 at 19:03:11:

Two things. A 1.2K tail resistor in your LTP won't be very effective. You want a very high resistance in the tail to minimize current fluctuations. Second, the 12AX7 isn't a suitable choice of LTP driver. It doesn't have the current capability to drive effectively 6V6-equivalent tubes.

What you do with the second grid of the 12AX7 confuses me. You should connect it to ground. I don't know why you'd put it where you do, and I don't know why you use 1M resistors.

The very small size of your coupling capacitors will also affect low-frequency response. I haven't calculated it but generally .1uF is on the smaller end of sizes you'd see, and .47 or even 1uF is a much better idea. You should also either ditch the .05uF/270K RC filter at the input, or also increase its size for frequency response. Also, the less caps in the signal path, the better. Phase shift or something, I haven't learned all of it yet :)

Finally, you might want to increase the cathode bypass cap for your AC/PEN tubes, by at least 4 times or so. 220uF to 470uF is generally a better size, because low frequency response is limited with lower values.

What does your power supply look like?

I hope that some of the advice I give you might help out the sound. Good luck! got any construction pictures?

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