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Early Broadcast Equipment

1847 Iconoscope Camera from Iowa

This page will document the progress in restoring a recently discovered television camera. It is apparently modeled after the camera descibed in the October 1940 issue of QST magazine. It uses the 1847 RCA Amateur Iconoscope, and was designed for narrow bandwidth amateur use (30 fps, 150 lines, 200 kHz) and a 902 CRT. Much of the information comes from a discussion topic at the Antique Radios forum.

The camera/viewfinder from the QST article

March 1, 2015

I have a wonderful artifact that I've been given the task of restoring to working order. It is a circa WWII experimental TV camera made by students and teachers at the electronics department at Idaho State University. It is a version of a 120 line camera that is based on these plans. It uses the 1847 Iconoscope tube and a display crt on the unit's chassis (the only remaining part of the camera) with the video amplifier chain.

My semester project is to get this camera running so they can be shown at events for the Robotics and Communications program. I wanted to throw this out here for some input and any expertise if people have seen this system before. The plan me and my teacher have come up with is to build the missing power supply and sweep driver circuit. Since it doesn't have the driver unit it should be easy to make it work on ntsc standard timing. I'm working on programming a PIC18 microcontroller to be a sync generator and simple ramp generator and high voltage amplifier to drive the deflection plates. The 600v, 300V, and filament supply is simple enough.

The worry I started having was about the limitations of the iconoscope. I was wondering about the effective frequency response of the tube, if that's the right term. Will the camera function well at the increased frequency? The tubes will deflect yes, but will the capacitive target still work well? What is the light sensitivity of the tube so I can properly meter the exposure?

I hope to update with my progress when I start work on it.

The 902 and 1847

March 2, 2015

I've been studying the schematics more and looking at what I have in my junk collection and am pretty sure I have almost everything I need to build the sweep and power supply with tubes pretty close to the original. I have a ton of 6SN7's that seem to be pretty much identical to the older types on the schematic and almost everything else I can scrounge up. The only thing I have yet to get is a second plate transformer for the 600V power. The only worry I have is some of the inductors and coils are old types that I may need help finding a substitute. Any help with that would be much appreciated.

To have a display all I really need is a scope and a slightly modified version of this tv to scope circuit :http://www.electronixandmore.com/projects/tvtoscope/. That way we can have it running on one side of the room connected to a cable going accross the room to a "receiver" to look at.

March 15, 2015

The T1 coil for the H osc is an RCA 9852 output transformer they're using as a center tapped inductor might be difficult. I think is says to remove the keeper or bar from the E shaped core. That seems like an important part that I need to find one so the characteristics can be the same. I did locate the other choke used in the sync amp section and I have some power chokes and I'll be fine finding the other power transformer (it pays to be a junk collector).

ETF commented: T1 is an audio output transformer used in RCA radios of the era. They should be easy to find. Post a message on the Antique Radio Discussion section of this forum and you will probably find one.

I've made two posts on other pages looking for the output xformer for the h osc and. The 1080 h choke, no luck so far. I was searching back in my junk and found a new 100 h choke from when I ordered 2 to replace the audio choke in a signal corps wavemeter in case I had to modify one to match it better. Do you think that would be adiquate for the circuit? I would think 100 h would block that frequancy well enough?

I have the chassis almost all drilled out for the hardware, will post a pic after I fold it all up on the box and pan brake.

April 15, 2015

I had to make do with some substitutions with the parts for the driver unit, but the substitutes seem to have worked well. I built the driving and power unit using the methods an experimenter of the day might have used. Most of the holes in the aluminum for the chassis where punched using a metalworking punch. After cutting out all the required holes and laying out everything I used a box and pan brake to bend the sheet into a sturdy chassis. I designed it so that both the units stacked and are secured together so that one part of the camera cant be lost again.

I used another output transformer for the horizontal oscillator inductance and played around with the capacitance until I found the right value. It's quite neat, the transformer vibrates the chassis and I could hear the change in pitch as I used a trimmer cap to dial in the frequency. The blanking differentiator seems to work well with a 150 H coil I found and some slight changes to capacitances. I'll have to see if it works when I get it all up and running.

I stuffed the old caps and fixed a few sloppy wiring jobs in the old unit. I improved the shielded Ike output line by using some old shielded "grid" wire I found and matches the look of the work.

CRT scanning is now working, as per the articles I put the CRT in the Ike socket and used it to do a preliminary centering and adjustment. I tested the video amp with a test frequency and it seems to work fine, although it gets very noisy and starts to oscillate ate high gain. Think that's normal?

I've been trying to get an image but all i can get is a faint square dip in the signal corresponding to some tape I put over the face, it will move back and forth as I move a flashlight back and forth, so I know its functioning somewhat. I just cannot get any image with the lens in place.