May 12th, 2020, 1:29 pm
David McGown wrote:Grover,
One thing I noticed about the Kiebert article is that he used the 5687 at the same current at the 6SN7 it replaced. Plate resistors are 50K. That is really a poor operating point for that tube, it really need more current for linearity. Which is why I currently have 20K plate resistors (for the original planned ECC99). What did you use, if you remember?
David
May 26th, 2020, 8:37 am
May 26th, 2020, 11:55 am
May 26th, 2020, 12:44 pm
May 26th, 2020, 1:16 pm
May 26th, 2020, 3:29 pm
May 26th, 2020, 9:09 pm
May 27th, 2020, 9:20 am
May 27th, 2020, 9:38 am
David McGown wrote:This circuit is a LF step (cut) circuit (Grover, you are right about that, I mistakenly thought the effect was at high frequencies). It basically limits the LF rolloff of the coupling cap, wiht the cap acting into the grid leak resistor defining the bass cut frequency, and the cap in parallel with the bypass resistor defining the stop.
The Hafler circuit used 0.22uF || 1M -> 100K, which gives a 7.2 Hz corner for bass roll off, stopped at 0.72 Hz
The Keroes circult used a 0.22uF || 470K -> 47K, which gives a 15.4 Hz corner for bass roll off, stopped at 1.54 Hz
My substitution of the 0.47uF cap results in the same bass roll off and stop frequency as the Hafler circuit. Therefore, I believe I am OK with respect to the original Hafler circuit (using the Dynaco A-430/A-431 iron, whereas the Keroes is using Acro TO-330).
May 27th, 2020, 11:05 am