need help with RCA MI-4877 cutter

[johnnylaclar]

Hi Everyone.

I have most of an old RCA overhead cutter.
Model: MI-4877
Type: 72-C
Head: MI-4887

I have the overhead carriage mechanism which seems complete and the head so far seems to be working. The feedscrew appears to be a very course thread and drives the head inside-out. I think this was made to cut 16".

I am trying to drive this with a Numark TTX turntable, but I'm having some trouble getting things mounted and aligned. Mainly, I don't know if the weight of the cutter carriage should rest on the spindle of the turntable or not. (or should there be a support bar that carries the load, and the spindle is more for guidance.)
The TTX spindle is pointed rather than rounded and I think that may be screwing things up..but this is all speculation.

Does anyone have photos, brochures, schematics or info for this make? Has anyone retrofitted one of these? I think even a photo of a complete unit will help me.

Much Appreciation to this community!
Jeremy

[JayDC]

do not thing that turntable has enough power to turn the overhead, a Technics 1200 doesn't even have the power..

one end of the over head goes to the center pin of the platter, the other side is mounted to a base.

if you decide to sell your head for any reason, contact me in private.

The only way to do what you want to do is to get a better turntable *technics sp10mk3 or sp15* and find a variable speed low rpm high torque motor and speed control to mount to the over head. It a little involved of a project, and could cost some money, but you would have a nice cutting system with variable pitch width like more modern lathes use.

not an impossible task, if your patient and have some money.. There are easier ways tho.

[johnnylaclar]

the TTX drives everything quite well so far (although the digital pitch control on the deck has suffered as a result.)
a nice new motor would be a sweet way to go for sure -and I would worry less about noise from the ttmotor getting into the recordings. but I'll have to get much more crafty about mounting.

thanks for the reply.

[JayDC]

I dunno if you taking into account the drag from the stylus when cutting..

[johnnylaclar]

jay-
you're right; I haven't gotten that far yet. only tried to simulate drag with my fingertip.

[JayDC]

my presto has enough torque to seriously hurt your arm, if you held the platter and turned it on. My technics don't even come close.. I have heard complaints on systems that have high fidelity but use a DJ turntable, usually because of the turntable. The vinyl recorders guys have an optional high torque turntable for their system, and the kingston dubcutter has a modification to get more torque from the 1200..

from what I've learned over the years from reading this forum, for what you would like to do, nothing beats a technics sp10mk3

This is what your overhead goes to:

[opcode66]

Yep, JayDC is correct. High torque = Low Flutter. That's what you want.

Cutting on a technics (1.5 kg-cm), even with the resistor mod (2.0 kg-cm), just isn't enough torque to avoid audible flutter.

An sp02 mk3 provides 10 kg-cm of torque. That is a lot! An Sp03 will give you 3.5 kg-cm. Those are the numbers though.

[johnnylaclar]

it seems I can get into a variable speed dc motor to drive the overhead pretty reasonably, but damn those sp10's are pricey!!

I have the motor and platter from an old meissner suitcase model. It would do the job, but I want to get away from the idler wheels if possible. I don't think I could ever figure out the math to make pulleys and whatnot.

Thanks for the help (and the pic -that's a beast of a unit.) -I'll keep picking away at this.