The 845 is not interchangeable with 211. The only mod you will have to to to your Cary 805B is changing the anode resistor to proper value. The primary on the 805's output transformer is really better suited to 845 anyway ( about 7.5 K Ohms if memory serves ) The 211 wants at least 10K. There are other 211 amps that use as high as 20K. Kirk can give you the resistor value you need. Technically the 845 was designed as a Class A Audio power amplifier. The 211 was not designed for audio service. I hope this helps.
