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#1
07-28-2008, 06:13 PM
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Eckhard, That Emiscope CRT is very interesting. Any chance you will let RACS try to rebuild it? Of is it too rare to risk ti?
__________________
John Folsom 
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#2
07-29-2008, 05:34 AM
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John: I don't know how many of these Emiscope CRTs survive. If a safe rebuilding is possible, I would do it. But there are many unresolved problems.
Another problem is the aluminising of the phosphors to prevent ion burns. But a CRT with 2.5 KV EHT might be very dim with an aluminised screen? I am in contact with RACS in France. When the CRT breaks during the rebuilding process, it is lost. No one would give me money for a broken crt. Here is another interesting CRT: http://bs.cyty.com/menschen/e-etzold...FB_VI-1_01.jpg http://bs.cyty.com/menschen/e-etzold...FB_VI-1_02.jpg http://bs.cyty.com/menschen/e-etzold...FB_VI-1_03.jpg http://bs.cyty.com/menschen/e-etzold...FB_VI-1_04.jpg This is also a candidate for rebuilding. I had taken the photos with the mobil phone hence the low resolution. The accus of the camera were empty. - Eckhard
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#3
07-30-2008, 05:06 PM
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Hi,
tonight I have tested the Emiscope 3/2 to see whether it has an ion burn. I could get a bright screen with only a light shadow of an ion burn. This might indicate that this CRT was not very often used for television. The Emiscope and the Erlenmeyer flasks are made of the same material: Pyrex, Duranglas or borosilicate glass. Erlenmeyer flasks are very cheap. Would would it costs to built a new Emiscope 3/2 or 3/1 CRT, made out of an Erlenmeyer flask? Kind regards, Eckhard Last edited by yagosaga; 07-31-2008 at 05:45 AM. Reason: add note about Erlenmeyer flask
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#4
11-13-2008, 08:08 AM
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Hi,
Steve Mcvoy has found a television picture tube for my Marconi set, a 7BP4. So, I could replace the radar tube with the 7BP4. Thanks to Steve for finding and sending it to me. The 7BP4 is of the same design as the 7BP7, but with a different phosphor: http://bs.cyty.com/menschen/e-etzold...ATestcardC.jpg http://bs.cyty.com/menschen/e-etzold...ctureDVB-t.jpg Hugo Holden has made some suggestions for changes. I did - short out N-81, but connected focus coil with 81. - Attenuator added (R-C at the cathode of the CRT) due to the higher gain of the CRT. - two 2M5 resistors were added parallel to R64 (bleeder chain) and CRT screen grid was connected with the middle point of both 2M5 resistors. I get 200V at screen grid, and when I switch off the set, the brightness on the screen disappears before the picture become a small spot which could damage the phosphor. - I have added an internal vertical blanking with 10nF at the plate of the vertical output valve and 250K in series at the cathode of the picture tube. With this modification, I can lower the contrast and increase brightness without retrace lines on the screen. - The X41C was weak. I have replaced the valve with a X41, one with a bakelite socket. This new valve provides more amplification than the valve before, I have to lower the R.F. input to -10 dB to get a clean picture. Otherwise I have moire and strong sound hum bars in the picture when contrast is fully turned on. - I have replaced C64 with a non-electrolytic high grade film capacitor. I have kept the original cap on the chassis. Now I have no cracks and white spots in the picture. The original one has shot my U52. Here are some recent photos of the chassis: http://bs.cyty.com/menschen/e-etzold...th7BP4A_04.jpg http://bs.cyty.com/menschen/e-etzold...th7BP4A_03.jpg http://bs.cyty.com/menschen/e-etzold...th7BP4A_05.jpg Kind regards, Eckhard
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