Re: MCP and CRT Readout

Don Black <donald_black@...>

That's interesting Ignacio. I worked on three Marconi Mk IV cameras as maintenance technician and can't remember the orbital function at all. I guess it was just never used and I didn't notice it. One of the cameras is now owned by a fellow member of the HRSA (Historical Radio Society of Australia), I'll try and remember to ask him about it. You live and learn.

Don Black.

On 30-Jul-13 10:51 AM, EB4APL wrote:

Hi Don,

I worked in the late sixties with both Marconi and Pye, and also with Fernseh, Toshiba and Thomson cameras.  The Marconi Mk IV had the orbital function and also a switch for turning it off, only used when taking a title or so.

Ignacio EB4APL

On 29/07/2013 3:42, Don Black wrote:

That's interesting Ignacio. I guess from your email address you're in Spain (I'm in Australia, though my ISP doesn't have the AU tag available  grrr). I think I've heard of the "Orbital" function but the cameras I worked on (Marconi and Pye" didn't have it. What cameras do you know used it?
I guess the scopes could be fitted with something similar, at least for moving the readout around. It might be a problem moving the trace it you were trying to line it up with the graticule to take measurements.

Don Black

On 29-Jul-13 11:18 AM, EB4APL wrote:


The mention to Image Orthicons reminds me that the cameras that used them normally had a feature called "Orbital".  This was a device that avoided that a static image could became fixed to the sensitive target making the tube useless.  I think that some of them used a motor to slow drive (1 cycle per min or so) a potentiometer to send sine-cosine currents to a pair of deflecting coils.  The image movement was quite small but enough for saving the TV camera to become a photo camera. 
This could be done for MCP scopes and wisely designed it could operate only when the readout was in action without affecting the normal traces.  Maybe it is a good idea for a backwards patent that now is useless.

Ignacio EB4APL

On 29/07/2013 1:21, Don Black wrote:

I don't have experience with MCPs but their glass channel wear out sounds similar to the problems with Image Orthicon camera tube targets. These are thin glass discs that have an electron image built up on the lmage side which has to leak through the glass between scans to form a charge on the scanned side. The original targets were made of doped glass that was slightly "ionic"conductive and they only had a life of a few hundred hours before they wore out as their resistance increased. A different type of glass was introduced (by EEV I think) called Elcon (electron Conduction) that used a resistive mode and that increased tube life ten fold plus was much less prone to "sticking" (image retention) than the old type. I guess similar developments were made to the glass channels in MCPs.

Don Black.

I mean later MCP CRTs which are still used in some specialized
applications. I base this on the links posted here in a MCP
discussion thread some time ago which discussed MCP lifetime and
wearout mechanisms. I suspect the MCPs Tektronix used had unusually
short rated lifetimes but maybe they wear out quickly because of how
they are applied.

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