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RE: 6as7 "preamp".

Posted by Tre' (P) on April 9, 2016 at 12:59:00

In Reply to: 6as7 "preamp". posted by gavinhaley on April 9, 2016 at 12:48:36:

The CCS plate load results in a more horizontal load line for the 6as7 which will give less harmonic distortion.

"Unfortunately, at first glance, these tubes don't look linear. In a normal resistor-loaded, grounded-cathode amplifier, they have high distortion, mostly even harmonics.
This distortion decreases with increasing plate load resistance, but a larger resistor means that you need a higher supply voltage. Luckily, there is a way to present a very high load to the plate of the tube without using a big resistor and high voltage power supply, a constant-current source (CCS) load."

A large value resistor would be fine but would require a high wattage resistor and a lot more B+.

If we assume that the EL34 based CCS provides a 1meg ohm load to the 6as7's plate,

A 1meg ohm plate resistor with 50ma. of current flowing through it will drop 50,000 volts and that will produce 2500 watts of heat.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 04/09/16 04/09/16 04/09/16

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