Quote:
Originally Posted by Robert Gribnau
I am not sure what you mean by the first schematic. If it is the schematic of the tweaked Brimar tone control, than the 12AX7 section has its grid returned to ground through the 470K and 2.2 M resistors. The grid of the 12AU7 section following the 12AX7 is directly coupled to the anode of the 12AX7 and therefore does not need a grid resistor.
Like I wrote, I think that the gain of an EF86 in triode mode is not high enough to cover the range from - 15 dB to + 15 dB. An EF184 in triode mode (mu is about 60 so the gain can be about 40) would be somewhat better. I have never used the EF184 before but I have read that the EF184 can be microphonic.
I hope some other forum members join in because the precise workings of tone controls is a little over my head (except in guitar amplifiers, I never build tone controls in my projects).
|
It was this one here.
https://www.angelfire.com/electronic...e-fig-06-1.gif
I think you are looking at a different schematic.
There is a 1M from the grid to ground and perhaps thats what im missing?
I hear alot say the EF86 is microphonic too, im not sure if there is much difference between the two in regards to microphony.