RCA MI-11850C Cutting Head
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
RCA MI-11850C Cutting Head
Does anyone have any information on the RCA MI-11850C cutter? I came across one that's NOS, but without literature. It has a plug with 4 pins so I'm assuming mono with feedback, but not sure. Haven't disassembled it to look at the coils or wiring yet since I have no lit on it. This is the long, gray head that was sold with the lathe attachment for the 70-D (and other) turntables. Can anyone shed any light? Thanks.
RCA cutter
I've used one of these heads and they're OK, but not as good as a Grampian feedback head. They were primarily for radio transcriptions. The head takes a short shank sapphire like Transco's 362 (or a 462 cut off). I usually order their 462's and cut them for short shank heads.
-
grooveguy
- Posts: 432
- Joined: Thu Jun 22, 2006 5:49 pm
- Location: Brea, California (a few miles from Disneyland)
- Contact:
RCA MI-11850-C
The RCA MI-11850-C cutterhead has passing mention in the 1952 book, The Recording and Reproduction of Sound by Oliver Read. This was my 'bible' and wish book when I was in Jr. Hi school in the '50s. The cutterhead illustrated seems to be a horizontally-mounted head to fit the RCA 73-B lathe, although it may also have been made available in a more standard vertical format to fit other lathes. The head has a built-in heater and thermostat to keep the damping material at a uniform temperature and consistency (the other two wires). Response is claimed to be ±2dB, 30Hz-10kHz.
-
grooveguy
- Posts: 432
- Joined: Thu Jun 22, 2006 5:49 pm
- Location: Brea, California (a few miles from Disneyland)
- Contact:
Hey, emorritt, I can help here. The Oliver Read book I cited earlier has a schematic of the RCA deck and shows a 6-volt transformer supplying power to the heater in the head. The same transformer also drives two pilot lights, one of which may be part of the Spencer microscope mounted on the RCA 73B lathe. I could scan this page and e-mail it if you give me an e-mail address.
The schematic also shows a 7-ohm resistor that can be switched in series with the head heater. The switch is simply labeled HI - OFF - LO. There is nothing in Read's text to tell when the heater would have been switched off, maybe on hot summer days? I would assume the HI and LO settings are for different environments also; the LO setting keeping the thermostat from cycling the heater on and off too frequently.
Although RCA was smart to make this heater part of the cutterhead, most of the damping materials used in those days were fairly temperature-stable, and probably really had to be heated up only when used in cold environments.
The schematic also shows a 7-ohm resistor that can be switched in series with the head heater. The switch is simply labeled HI - OFF - LO. There is nothing in Read's text to tell when the heater would have been switched off, maybe on hot summer days? I would assume the HI and LO settings are for different environments also; the LO setting keeping the thermostat from cycling the heater on and off too frequently.
Although RCA was smart to make this heater part of the cutterhead, most of the damping materials used in those days were fairly temperature-stable, and probably really had to be heated up only when used in cold environments.
Hello! I see that you have information about RCA 73B. I have big problem with adjustment this recorder... Please send me on email (send in pm) any information about RCA 73B and record head MI-11850. I shall very much thanked you! Beforehand thanks!!!grooveguy wrote:Hey, emorritt, I can help here. The Oliver Read book I cited earlier has a schematic of the RCA deck and shows a 6-volt transformer supplying power to the heater in the head. The same transformer also drives two pilot lights, one of which may be part of the Spencer microscope mounted on the RCA 73B lathe. I could scan this page and e-mail it if you give me an e-mail address.
The schematic also shows a 7-ohm resistor that can be switched in series with the head heater. The switch is simply labeled HI - OFF - LO. There is nothing in Read's text to tell when the heater would have been switched off, maybe on hot summer days? I would assume the HI and LO settings are for different environments also; the LO setting keeping the thermostat from cycling the heater on and off too frequently.
Although RCA was smart to make this heater part of the cutterhead, most of the damping materials used in those days were fairly temperature-stable, and probably really had to be heated up only when used in cold environments.