Is 845 a direct replacement for 211

Is it possible to install 845 tube in place of the 211 in cary 805B. Are they interchangeable? Is there any modification required to make this possible?
I also have Cary 805B monoblocks, no you can't use the 845 instead of the 211 without a modifications. Cary will upgrade to a 805C for 2500.00 or they can just make a change with a switch which allows you to use 845 output tubes without the full mod. to 805C. I replaced the stock 211 tubes with NOS RCA 211s and it was a major improvement. I had a chance to take home a pair of 805C for the weekend for a trial. While they sounded different than the 805B, I can't really say they sounded better in my system. I decided to stay with the 805B. You can contact Kirk at Cary or feel free to e-mail me with any questions.Good luck
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.