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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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7th Oct 2005, 10:05 pm | #1 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,518
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Cossor 926 The resurection continues!
Hi All,
Following the bungle on my behalf with the previous thread relating to a mysterious 962 model, I have started one with the proper title!! Ok, progress so far: Sourced and fitted all valves except the 7c5 (a 6v6 is now fitted in its place) Chassis run up on mains - No ht - traced to phantom spares recovery robbing dropping resistor.... resistor replaced, HT announces it's presence by rupturing a .001uf moldseal type thing in the rf deck...... Try for some hum on the audio stage - suprisingly quiet - oh dear, no HT again - 1.5K anode feed resistor inexplicably missing...... , so fit new anode resistor, and some sort of hum is available, but very quiet - finger on grid of audio bottle yields a pathetic click...... Attempt to measure cathode volts 87 volts? er maybe not - solution - fit missing cathode bias resistor....... now have a much more respectable 6.5 volts, and oodles of hum with the trusted MK1 signal injector (index finger left hand) Ok, time to fit the 185BT line ouput bottle, and attach some form of tube. Result - fantastic lightning storm from anode cap of tube - clean using some IPA (no, not beer - far to precious to waste ) then dry well with paper towel - lightning ceases. No raster though - cathode volts measure approx 120 volts, first anode 55v?? Ok tele experts where to now? Cheers Sean
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Engineers make things work and have spare bits when finished |
9th Oct 2005, 10:06 pm | #2 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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Re: Cossor 926 The resurection continues!
OK, I have a dim raster - crt volts as follows
A1 395v G 135v K 130v A2 draws a 20 mm spark so plenty of volts there....... I wonder if the crt is a bit tired, as I have to flog the brightness flat out.... Any ideas? Sean
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Engineers make things work and have spare bits when finished |
9th Oct 2005, 11:08 pm | #3 |
Heptode
Join Date: Jul 2003
Location: North Walsham, Norfolk, UK.
Posts: 516
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Re: Cossor 926 The resurection continues!
hi yes you should have a bright raster with those voltages have you tried a signal on the set? dont panic yet as the tube will probrably come to life with use! does the grid to cathode volts vary with the brightnes control? .
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10th Oct 2005, 8:59 pm | #4 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,518
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Re: Cossor 926 The resurection continues!
Right then, I have been through the whole set now, and replaced pretty much all of the capacitors (ive never used so may .001s ).
I can get a good amount of audio through (well, after I figured there was a short to ground in the volume control.....), and I can get some sort of signal through the video stages, however, I still need to run the brightness and contrast at full blast to do so..... So, do I leave the set on to cook the tube up for a while, or do I start to look into a replacement CRM121? All the tube voltages appear to be reasonable, and if you measure between grid and cathode you can see a change in voltage when a signal is present, as well as when you vary the brightness control... Still, I am pretty pleased, as originally the set was offered as a spares donor.... Any words of wisdom? Cheers Sean
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Engineers make things work and have spare bits when finished |
10th Oct 2005, 10:02 pm | #5 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
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Re: Cossor 926 The resurection continues!
More to add.....
I fired up the "Darius Modulator" (ought to be a registered trademark! ), and after some faffing around with the controls I managed to get some sort of picture, It appears to be split vertically across the screen though, is this a sync problem? I also have problems with the width of lines, the picture is visibly spread too large, and no adjustment cures this. I cannot post a screenshot unfortunatley, as the tube is too dim for the camera without a flash, and with the flash well, a whiteout occurs! Cheers Sean
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Engineers make things work and have spare bits when finished |
11th Oct 2005, 10:20 am | #6 | |
Retired Dormant Member
Join Date: Dec 2003
Location: Solingen, Germany
Posts: 727
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Re: Cossor 926 The resurection continues!
Quote:
Kind regards Darius |
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