Ok - at some point I'll post the line status and hold schematics. I now refer to the former A lead as the H lead, + present when pressing the hold key while going on hook. The line in use indicator is a basic opto-isolator circuit, hold is 2 relays. From what I read about 1A1 systems the hold circuit may be based on that, also very basic. I now use the doorbell transformer to power the lamps. It's 18vac, so there's 2 diodes in series to drop it a little. Yes the lamps will dim when both the CO and intercom are in use. There is no longer a bathroom phone, but do like being able to pickup in the garage and cordless phone. I don't have my basic caveman cellphone on me when I'm home. I much prefer talking on tip & ring.
I just read AT&T is selling out all landline facilities in my state to another company, Frontier. I hate to do it but looking at Frontier's rates I may need to finally retire my analog CO line and consider voip, but would want an analog adapter for the key system. Quite a few choices available, will need to do some research.
