ALTEC 527A Mic Power Supply Info needed

I'm looking for informations about the ALTEC 527A tube microphone power supply. It looks it could be used with the M20/M30 lipstick microphones systems but it has a much more elaborate circuit than the original 525A power supply,with adjustable and regulated polarizing voltage and heater current,including two very nice meters. There are many tubes inside (6CG7/6AU6/ (2)5651 and a 1HT4 current regulator ballast tube) My guess is that it was intended to be compatible with either the 29A or 21D capsules by adjusting the polarizing voltage (60 volts for the 29A and 200 volts for the 21D) but why the heater current is adjustable is still unclear to me. Does anybody have more informations about the 527A and  which microphone(s) it was designed for ? It looks more like a special purpose (instrumentation,medical,industrial ?) unit and unfortunately has no balancing/matching output transformer built in.  A copy of the schematic/manual would be great since I was unable to find any informations about this model so far on the web. Thank you for your help and advices.

How about a 527B?
http://twin-x.com/groupdiy/displayimage.php?pos=-4556

Thanks for the info. Very helpful. Looks like the only differences are that the "A" version doesn't include the (4665) output transformer socket and has a plate voltage meter which has been changed to a plate current meter on the "B" version. From the schematic I can see this power supply was intended for the 21BR capsule which is a measuring (instrumentation) microphone. This should explain the more elaborate (regulated) circuit used in the 527 power supply,needed for calibration and laboratory use. It can probably be used with other capsules requiring a 200 volts polarizing voltage and a 165A microphone base (M30 "lipstick" system), the Cannon socket pin assignment being the same.   

Crusty2 said:

How about a 527B?
http://twin-x.com/groupdiy/displayimage.php?pos=-4556

Click to expand...

Anyone have this schematic? Olde dead link.