Tube DIY Asylum

"reduce the harsh distortion reasonably"

172.11.32.65

Chip647

A

In Reply to: RE: Which one do you choose ?CCS plate load or Degeneration (local feedback) posted by Eric Chan on October 04, 2023 at 10:13:30

If you have harsh distortion, you have a basic circuit design issue. Band aids won't really do much.

Just for fun, find out the answer to these 3 questions:
1. What is the grid to cathode bias voltage?
2. What is the signal voltage applied to the grid?
3. What is the load (resistance and capacitance) on the output?

Then get a fast scope and look for oscillations.

Follow Ups:

RE: "reduce the harsh distortion reasonably" - Eric Chan 20:18:13 10/04/23 (2)
The ECC99 at 90V, 6mA 24K plate R, -2.5V grid to cathode,
cathode unbypassed with a CLC 200uf 3H 200uF, nothing particularly, but if I bypass cathode with decent Audionote electrolyte cap then it sounds harsh and thin， (suspecting the insufficient idle current causing the harsh but no voltage headroom)

Wasn't distortion reduction being the necessary approach ?
- RE: "reduce the harsh distortion reasonably" - Tre' 07:01:14 10/05/23 (1)
  "insufficient idle current causing the harsh but no voltage headroom"
  
  I would think so. Sorry, I can't draw a straight line but there is no reason to run that tube so cold. You are down in the mud where the grid lines bunch up. That is the cause of harmonic distortion. You could be up away from the mud. Up where the tube is linear. 200 volts plate, 14 ma. into a CCS or a plate choke to give a horizontal load line and the distortion goes way. You will get more gain as well.
  
  Tre'
  Have Fun and Enjoy the Music
  "Still Working the Problem"
  - RE: "reduce the harsh distortion reasonably" - Eric Chan 06:29:32 10/06/23 (0)
    plate load choke was my first choice but difficult to source one, it does thing like active CCS
    
    degeneration or CCS load, which to choose ?

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