|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: RE: Cathode bypass cap removed and I like it posted by megasat16 on January 10, 2017 at 17:17:41:
"Are you saying the quoted RCA or any datasheets for the plate resistance is measured with the cathode bypass capacitor in place..."Yes.
"Cathode bypass restores the degenerative feedback lost by the cathode bias resistor."
If the cathode is grounded (no cathode resistor) then there is no degenerative feedback.Once there is a resistor between the cathode and ground, if that resistor is not bypassed then the AC (along with the DC) would flow through that resistor.
When AC is flowing through the cathode resistor an AC voltage at the cathode is generated that is out of phase with the input signal at the grid.
The AC at the cathode bucks the input signal at the grid and is called local current feedback (degenerative feedback).
A properly sized cathode bypass cap insures that only the DC flows through the resistor. The AC flows through the cap because it's reactance represents a near dead short to AC and at the same time will not pass DC at all.
"My understanding is that you can safely remove the cathode bypass cap without effecting the plate resistance."
That is just simply not true. Current feedback increases the plate resistance. Voltage feedback decreases the plate resistance. Either way, the plate resistance is always effected by FB.
"The damping factor may be effected as it is calculated on the output from the amp and the amp without the cathode bypass cap has lesser (Volt or Power) output than the one with it."
No.
The damping factor is the reflected impedance of the primary divided by the plate resistance. It has nothing to do with voltage gain or power.
A amplifier that uses a 2a3 (assuming an operating point that yields a plate resistance of 800 ohms) connected to a output transformer that has a 2500 ohm primary has a damping factor of 3.125
If the output transformer were 5000 ohms the amp would have less power and less gain but the damping factor would be 6.25
Degenerative feedback will increase the plate resistance and that will decrease the (already marginal) damping factor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 01/10/17
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: Cathode bypass cap removed and I like it - Tre' 20:33:59 01/10/17 (1)
- RE: Cathode bypass cap removed and I like it - banpuku 07:28:32 01/11/17 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
