Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Ekco T.U. 211, A possibly pointless restoration!
Lloyd said
Well, those resistors are probably working right on the edge of their voltage rating! I've looked them up on Rapid's website, and they are rated max working voltage 250V, max overload 500V. It doesn't state AC or DC. Anyway, I'll not use the set until I've got replacements.
Use Vishay VR37 or HVR37 (3500V DC) - in both cases the RMS ratings are √2 less. There are also equivalents by Welwyn.
At least you have it under control now.
Frank
Lloyd said
It was interesting to note the effect of A1 voltage on the picture, lower voltage made the picture more contrasted, but poorer focus, and higher voltage made the contrast more washed out, and flyback lines appeared. Now that's where things get unclear to me, as in the link above, it says that the A1 voltage needs to be +200-400V with regard to the cathode, so does that mean that I would be measuring between the cathode and A1? I was assuming it would be between chassis and A1. Also, the cathode in this set sits at about +160V.
By universal agreement in the industry all CRT electrode voltages are measured WRT (With Respect To) the Cathode.
To cut-off the beam the grid (also called Grid1) must be negative (WRT the cathode), by 40 - 80V typically.
For video display (i.e. TV and the like) there's two ways to drive the CRT, Cathode or Grid. The cathode is more common, as it requires less drive voltage swing compared to G1 drive, but requires inverted video (making the Cathode more negative brightens the picture)
An easy way to get G1 more negative than the cathode is to elevate the cathode by connecting it to HT, as in your case. Therefore all the other electrodes will need to be elevated by the same amount.
You've made some interesting progress, and landed a new CRT, that with a bit of wrangling will work well in this project.
FordAnglia said
For video display (i.e. TV and the like) there's two ways to drive the CRT, Cathode or Grid. The cathode is more common, as it requires less drive voltage swing compared to G1 drive, but requires inverted video (making the Cathode more negative brightens the picture)
I would point out that the reason for cathode drive is that it being a lower impedance input compared to the grid, the frequency response is better due to the reduction in 1/2πCR frequency losses.
Also, I'm a little confused by your statement about ... The cathode [...] requires less drive voltage swing compared to G1 drive.
Surely, given that the beam current is proportional to the difference in potential between grid and cathode - the traditional method of measuring Ia/Vg characteristics - it makes not one iota of difference whether the drive is to the grid or cathode in terms of absolute voltage levels but merely the polarity?
Cathovisor said
FordAnglia said
For video display (i.e. TV and the like) there's two ways to drive the CRT, Cathode or Grid. The cathode is more common, as it requires less drive voltage swing compared to G1 drive, but requires inverted video (making the Cathode more negative brightens the picture)I would point out that the reason for cathode drive is that it being a lower impedance input compared to the grid, the frequency response is better due to the reduction in 1/2πCR frequency losses.
Agree with that. The cathode capacitance (to all other electrodes) is smaller, with less loading on the driver.
As high voltage PNP transistors are less common and more costly than NPN types, driving the cathode is practical.
In a colour CRT there are three channels, with G1 and G2 common to all three leaving cathode drive as the only choice.
Also, I'm a little confused by your statement about ... The cathode [...] requires less drive voltage swing compared to G1 drive.
Surely, given that the beam current is proportional to the difference in potential between grid and cathode - the traditional method of measuring Ia/Vg characteristics - it makes not one iota of difference whether the drive is to the grid or cathode in terms of absolute voltage levels but merely the polarity?
Logical but not always true. I don't have my copy of "How Television Works" (Holm) handy as I'm at work. My recollection is that as the G1 thimble surrounds the cathode it's job is to also focus the beam entering the G2 cylinder, giving rise to a non-linear relationship for Vg1 - Ik compared to Vk - Ik.
I hope that clarifies my earlier comment.
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