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Jeffrey D. Medwin... OTL question

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7 hours ago, babadono said:

What is the cathode bypass capacitor in the circuit for? What is it therefore?


It affects gain, frequency response, distortion reduces degenerative/local negative feedback.

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This might help some to understand how the cathode bypass capacitor affects performance of the gain stage whether in a preamp or amplifier output stage.

 

 

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On 9/11/2020 at 7:33 PM, mikebse2a3 said:


For those concerned about capacitors in amplifiers many SET amplifiers using a bias resistor in series with the filament also have capacitor/capacitors bypassing the resistor which the audio signals also pass through.
 

miketn

 

Yes Mike. 

 

More often in commercial amps we see an electrolytic across the Final's tube cathode resistor.   

 

This could be improved upon, in my own opinion.

 

How do you like to usually bypass a 2A3's Rk ??

 

Jeff 

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Nelson Pass's concluding statement,  his feedback article :  ( Suggest you read it all, very good. )

 

Pass.thumb.JPG.48430a4f62f9a0e1731865d6c3b86406.JPG

 

Notice,  ALL of his discussion seems to be based on measuring negative feedback's effects with SINGLE tones.  May I ask, is music comprised of single tones ??   Hardly !!!!!   Poor E.E.s, it's hilarious to me . 

 

Another point of Nelson's I love, keeping in mind that triode vacuum tubes can be fairly linear , VS other amplifying devices :

 

1847681313_PASS2.thumb.JPG.2ac8a45d6cba802da912ea975f07d377.JPG

 

 

              I always like to say, " All the King's horses, and all the King's men, could never put Humptey together again. "

 

                                                   You may deduce easily today, who I learned that from !!!!!

 

                                

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There are 2 ways to reduce distortion in SEP amps.  One is to use it at a fraction of its maximum output power, and the other is to use nfb.  I prefer the latter (as voltage fb) as it reduces the typically high output impedance as well as increasing the bandwidth.  If applied within reason, it does not ruin the resultant sound in my experience.  In fact, it can provide a very triode like experience in some systems.

 

 

Maynard

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On 9/16/2020 at 10:54 PM, Jeffrey D. Medwin said:

How do you like to usually bypass a 2A3's Rk ??


usually a film type. 
 

I also like to use fixed bias to eliminate the need for the RK/Bypass Cap.

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15 minutes ago, mikebse2a3 said:


usually a film type. 
 

I also like to use fixed bias to eliminate the need for the RK/Bypass Cap.

 

Thank you.  

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