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Switchable Cathode Bypass Capacitor for a Tube amp

Jim Nomad

Nov 26, 2012
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Hi All,
I am building a simple tube amp using ECC83, I read that the value of the Cathode Bypass Capacitor can have an influence on gain at different frequencies and headroom. Would it be possible to build in a switch so that I can switch between different capicitors and a a consequence produce fully / partially / un - bypassed effect . If so would attached circuit do the job ?
Many thanks

Jim
 

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Harald Kapp

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That should be possible, although I'm in no position to judge the effect.
I suggest you put the switch on the cathode side of the capacitor.
 

duke37

Jan 9, 2011
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The 1uF capacitor will give a turnover frequency of about 100Hz, the 2uF capacitor about 50Hz. I think the gain will rise as the frequency rises and be limited to about 10 times the basic amplifier.

If you wish to reduce the gain and improve linearity with a constant gain, then you can put a resistor in series with a large capacitor.
 

CDRIVE

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May 8, 2012
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If you wish to reduce the gain and improve linearity with a constant gain, then you can put a resistor in series with a large capacitor.

Good point Duke. This would be the most logical way (SOP) to do this. It applies to BJT's and JFETs as well.

Chris
 
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