[Konvas] Kinor 35 conversion

[Peter Haas]

On Feb 6, 2010, at 10:06 AM, Speedbirdmgh at aol.com wrote:

>
> The Mitchell camera does'nt seem to have any electronics as such  
> unless
> there is an additional add on box to control its speed.
>

The original Mitchells had either an interlock motor, 230 volts three- 
phase, or a combination interlock/direct current motor, the so-called  
*Multi-Duty* motor.

It is possible to crystal control a Multi-Duty motor, although these  
motors require 96 volts.

If there is no crystal-controlled regulator involved, 96 volts dc  
will give about 1800 rpm, from which the right angle drive within the  
motor unit gears-down to 1440 rpm, which is sync speed, 24 fps.


> I have a feeling that 'heat' could be the main cause of failure of  
> camera
> electronics but ofcourse if the initial design was wrong and  
> together with
> poor  quality control then its "doomed" from the time it left the   
> factory.

The *heat* is due to the pass regulator, which is in series  
connection with the motor armature.

The entire power load of the motor passes through that transistor.

It is phase-modulated, so the actual dissipation within the  
transistor, which must be rejected as heat, is about one-half, more  
when the battery voltage is on the high side, less when the battery  
voltage is on the low side.

The regulator will regulate down to a reasonably low value, after  
which the camera will lose sync.


All crystal controls operate similarly, although many will throw in  
many additional functions, such as digital readout of frame rate,  
digital readout of remaining footage, etcetera.

For good crystal control, the optical tachometer must have 40 or more  
pulses per frame. 80 pulses per frame is even better.

It is common to start with a color burst crystal and divide it down  
to about 9600 Hz.


If one was willing to give up the accessory functions, such as  
digital displays, you could replace a camera crystal control unit  
with two integrated circuits and a 2N3055 power transistor.