01-02-2019, 07:16 AM
Still plugging away at this amp but have managed to solve some issues. I've completely changed the drive and IP stage circuits. I did away with the cathode followers and am now using a very beefy LTP as PS and drivers using Russian 6H6N/ECC99's, a bit like a 12BH7, these are paralled, EG anodes, grids and cathodes are tied together. This will drive the amp easily up to and over 120w with only about 3v RMS IP - open loop gain.
For the IP stage I'm using another LTP but as a differential amp to deal with hum. IP isn't of the balanced type just a shielded twisted pair onto one grid with NFB going to the other grid. Ouput is SE off the non inverting side, this makes stability very good, since the change I've had far less issues with spurious oscillation. I'll do a new schematic when I get a mo.
Andy.
For the IP stage I'm using another LTP but as a differential amp to deal with hum. IP isn't of the balanced type just a shielded twisted pair onto one grid with NFB going to the other grid. Ouput is SE off the non inverting side, this makes stability very good, since the change I've had far less issues with spurious oscillation. I'll do a new schematic when I get a mo.
Andy.
