Resolving cold midrange in 5687 circuit

[Eli Duttman]

Still hoping for direction on bias/voltage

Dude,

Refer to the plate curves in the TungSol data sheet. The idea is to pick a plate current (I_B) well into the nicely spaced portion of the curves. Avoid the bent, non-linear, section. An I_B in the 10 - 15 mA. range seems highly suitable to me

 

[phrarod]

Hi Eli. I've never worked with tube curves so I'm not confident in reading them.

Since this is 2 tube sections do I need to try for that on both sections or just the final or first stage. See I'm confused.

 

[Mark Verhoeven]

I know it's an old topic, but I am hoping for an answer on my questions (all related to the AN 5687 pre-amp):

@pharod: you are talking about reducing the value of the grid stopper resistor. Do you mean the one which is 1K originally, or did you fit one before the grid of the 2nd stage?

@all: is it a good thing to add a grid stopper resistor before the grid of the 2nd stage? Is the value critical?