Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: clyde on January 20, 2024, 04:46:45 pm

Title: Frequency Response Variations with Bias Cap Size
Post by: clyde on January 20, 2024, 04:46:45 pm

I've read that bias cap size on fixed bias circuits affects frequency response, ie larger uf = lower frequency response.  This was new to me and can anyone confirm the process by which this occurs?

Title: Re: Frequency Response Variations with Bias Cap Size
Post by: sluckey on January 20, 2024, 04:59:15 pm

I've read green eggs and ham at least 500 times. Still don't believe it!    :icon_biggrin:

Title: Re: Frequency Response Variations with Bias Cap Size
Post by: PRR on January 20, 2024, 05:06:32 pm

Push pull or single-ended?

Competent designer or an idiot?

Title: Re: Frequency Response Variations with Bias Cap Size
Post by: clyde on January 20, 2024, 08:06:40 pm

On another board, new poster. 

Title: Re: Frequency Response Variations with Bias Cap Size
Post by: WimWalther on January 20, 2024, 08:51:32 pm

Quote from: clyde on January 20, 2024, 08:06:40 pm

On another board, new poster.

If you consider the fact that a typical bias supply is isolated from the grids of the power tubes (and the driver circuit..) by 220-330K per tube, any effects related to bias supply capacity / impedance are kind of out the door.

ETA: This claim also has implications for bias regulators** which can be modeled as true voltage sources or huge caps.

(** which no one should use anyway, unless B+ is fully reg'd..)