03-09-2021, 12:19 PM
(03-09-2021, 12:28 AM)Kalee20 Wrote:(01-09-2021, 05:16 PM)BusyBee Wrote: Your delayed amplified AGC sounds about right Kalee.
The outbid the DC amplifier is scaled and level-shifted and applied to the main IF amplifier screen-grids and suppressor grids.
The circuit is not optimised as yet - the various potential dividers could be combined, for instance - but it works!
Readers may raise their eyebrows at three power rails, however the 1.2V and 120V are standard LT and HT rails; the negative bias line is needed elsewhere (bias for 1p24b output valves) and also for a heavily-morphed infinite impedance detector, so it is already present.
It's an interesting circuit / approach which will give me food for thought. Thank you for sharing. Your negative supply line is maybe unusual but does not quite come out of the blue to me. My earlier mention/ idea of using an op amp in the AGC line would require similar to handle negative going output (for reverse biasing grids in the normal way). Normally in simpler sets this is derived from signal so it is not obvious. In many ways it may be another way of approaching what you have done but by taking reference from the main detector or signal relative point and having more involved processing. Although it does seem a bit involved at first look your three valves do make for a more traditional look. It will be interesting to see the full finished set.
Tracy
