Tube Cameras & associated faults - UK Vintage Radio Repair and Restoration Discussion Forum

channel405 · 25th Oct 2013, 12:02 am

I was going through my collection of old tube cameras. On powering up one of them, an Hitachi GP-4D (circa 1978?) with a tri-electrode vidicon tube just displayed a blank raster in the viewfinder CRT.

So I opened it up to see how many leaky caps I could find, which seemed surprisingly unleaky looking. I did notice however that on applying power, the tube at the base went distinctly purple. Now I remember reading this does happen with thermonic devices, but I can't remember why, does this indicate a fault with the tube itself or the voltages driving it? Thanks!

German Dalek · 25th Oct 2013, 6:11 am

Good morning,

Hows about a bad coupling cap or Anode-overload ?
I hope the tube is not gassy!

Happy week-end,

German Dalek

beamcurrent · 25th Oct 2013, 10:22 am

That tube does not look healthy to me, the start up glow of the heater should be a reddish yellow colour.

If you hold your finger near the tube target ( remove the lens) there should be a lot of interference and patterning if the video amp is working ok.

good luck.

Refugee · 25th Oct 2013, 8:58 pm

Usually when any tube glows purple as brightly as that it is not far from going to air.

I had an audio output pentode that glowed purple and a month or so later it went to air.

channel405 · 25th Oct 2013, 10:47 pm

Thanks all for your input (no pun intended!). I did try touching the target area but got no response. Anyway, looks like the tube then, I suppose these are unique vidicons being tri-electrode? Oh well, another non working static display then!

Nicklyons2 · 26th Oct 2013, 11:30 am

"reelguy" has an Hitachi HKC770 up for grabs - similar tube maybe?

25th Oct 2013, 12:02 am	#1
channel405 Tetrode Join Date: Jun 2004 Location: CH3, Blaen Plwyf Transmitter, Aberystwyth, WALES Posts: 72	Tube Cameras & associated faults I was going through my collection of old tube cameras. On powering up one of them, an Hitachi GP-4D (circa 1978?) with a tri-electrode vidicon tube just displayed a blank raster in the viewfinder CRT. So I opened it up to see how many leaky caps I could find, which seemed surprisingly unleaky looking. I did notice however that on applying power, the tube at the base went distinctly purple. Now I remember reading this does happen with thermonic devices, but I can't remember why, does this indicate a fault with the tube itself or the voltages driving it? Thanks! Attached Thumbnails __________________ 405 line TV, 1936- 1985 2007.........to the present day

25th Oct 2013, 6:11 am	#2
German Dalek Hexode Join Date: Jan 2011 Location: Düsseldorf, Germany. Posts: 368	Re: Tube Cameras & associated faults Good morning, Hows about a bad coupling cap or Anode-overload ? I hope the tube is not gassy! Happy week-end, German Dalek __________________ And now something completly different: MARC BOLAN, he was/is the real king of Pop Music!

25th Oct 2013, 10:22 am	#3
beamcurrent Heptode Join Date: Mar 2008 Location: Camberley, Surrey, UK. Posts: 805	Re: Tube Cameras & associated faults That tube does not look healthy to me, the start up glow of the heater should be a reddish yellow colour. If you hold your finger near the tube target ( remove the lens) there should be a lot of interference and patterning if the video amp is working ok. good luck. __________________ Regards Brian Visit the Virtual Broadcast TV Camera Museum

25th Oct 2013, 8:58 pm	#4
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,554	Re: Tube Cameras & associated faults Usually when any tube glows purple as brightly as that it is not far from going to air. I had an audio output pentode that glowed purple and a month or so later it went to air.

25th Oct 2013, 10:47 pm	#5
channel405 Tetrode Join Date: Jun 2004 Location: CH3, Blaen Plwyf Transmitter, Aberystwyth, WALES Posts: 72	Re: Tube Cameras & associated faults Thanks all for your input (no pun intended!). I did try touching the target area but got no response. Anyway, looks like the tube then, I suppose these are unique vidicons being tri-electrode? Oh well, another non working static display then! __________________ 405 line TV, 1936- 1985 2007.........to the present day

26th Oct 2013, 11:30 am	#6
Nicklyons2 Octode Join Date: Jan 2013 Location: Barnsley, South Yorkshire, UK. Posts: 1,517	Re: Tube Cameras & associated faults "reelguy" has an Hitachi HKC770 up for grabs - similar tube maybe?