20th Feb 2021, 10:03 pm | #121 | |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
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20th Feb 2021, 11:08 pm | #122 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
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Re: My first telly TV22
Basically increasing the contrast and or brightness causes an increase in beam current on the tube. Because the EHT comes from a fairly high impedance source, more beam current equals lower EHT. The Lower the EHT, the more easily the electron beam is deflected (because it is flowing to the screen more slowly), so the picture gets bigger and the focus is also affected for the same reason.
On the subject of attenuators, the TV22 is not a very sensitive set. I find that 6 dB is fine for a TV22 connected to an aurora or a hegdhog (I think that's how Frank spelt it). Cheers Andy
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20th Feb 2021, 11:23 pm | #123 | |
Hexode
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Re: My first telly TV22
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I tried both a 6dB and a 12dB with the Aurora and the Hedghog (I think I got it right this time!), but apart from the need to increase contrast a bit, I didn't really see any difference in the testcard. What should I look for? It would be great if you could post a before and after image. I do have a bit of overshoot on light/dark vertical transitions, but this didn't go away with the attenuation and I mostly attribute it to non-optimal alignment. Thanks! Helder Last edited by Helder Crespo; 20th Feb 2021 at 11:36 pm. |
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21st Feb 2021, 12:55 am | #124 |
Heptode
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Re: My first telly TV22
Hi Helder,
I don't think you will notice much difference in the bandwidth on this set between 6 dB and 12 dB attenuation, but some sets do start to show a bit of grainy noise in the picture at 12 dB. A set with too much signal will tend to have vision on sound and possibly sound on vision as well. The only y reason I tend to go for 6 dB is that it gives me enough signal to feed into an inductive Y splitter and run two sets at once. BTW, some set designs only applied the contrast/gain control to one stage which gives the effect (when staggered RF/IF tuning is used) of reducing the bandwidth as the contrast is increased. This makes for a set with a wide service area, but the effect on the resolution was definitely noticeable. Cheers Andy
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21st Feb 2021, 2:10 am | #125 | |
Hexode
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Re: My first telly TV22
Quote:
Cheers Helder Last edited by Helder Crespo; 21st Feb 2021 at 2:24 am. |
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21st Feb 2021, 10:47 am | #126 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
So I’ve checked out the contrast control and it seems to be doing what it should. The pot is fine and adjusting it controls the voltage on the cathode of V1/V2 as it presumably should.
I found I can reduce the contrast and then if I adjust the horizontal hold (I think , the left hand top knob on the front) I can get it to lock in ok , but raster shrinks and focus gets worse. Judging from the increase in corona hiss as I reduce the brightness I recon the EHT is dropping with increased beam current. At the moment I still have my string of IN4007s dangling at 8kv . I have a new EY51 and PL81 on order, anythink else I should be checking? |
21st Feb 2021, 10:49 am | #127 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
I have no attenuator fitted , is this something I can rig up with some resistors? Maybe a local hardware shed would sell them?
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21st Feb 2021, 10:56 am | #128 |
Hexode
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Re: My first telly TV22
This makes sense, as less beam current gives higher EHT, hence narrower raster. Have you readjusted the focus for these conditions?
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21st Feb 2021, 11:05 am | #129 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
Yes , to be honest focus lever doesn’t seem to have a huge effect , it’s also quite stiff , beam centering controls seem to work ok though
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21st Feb 2021, 11:06 am | #130 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
Have got an attenuator to collect from local DIY shed
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21st Feb 2021, 11:23 am | #131 |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
You should clean and lubricate it. It plays a key role. The lever should be able to move freely and smoothly along the whole range. I would say this is more important than attenuating the input right now.
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21st Feb 2021, 11:29 am | #132 |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
As a quick solution you can use WD40 to clean/free the mechanism. The moving part/tube (the one with the handle) is not threaded, even though it may seem it is at first glance, and simply slides in and out of the fixed magnet guided by the pin on the lever mount. This part can be removed by simply unscrewing the lever mount, which enables removing and cleaning it thoroughly. Don't disassemble the fixed magnet though. It's not necessary and it can affect its magnetisation.
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21st Feb 2021, 11:36 am | #133 |
Hexode
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Re: My first telly TV22
An important point: do you have your ion trap magnet close to the base of the tube (pin connector)? If it's too close to the focusing magnet, or touching it, the two magnets/fields will interact, which can be a problem, especially because your tube is mounted somewhat sideways, i.e., the tube's EHT anode is facing the EHT shield, instead of facing up / closer to vertical.
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21st Feb 2021, 11:46 am | #134 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
I have been reading the Bush service instructions and it mentions the need to tighten the locknuts after doing the screen centering , to prevent image moving about with focus adjustment. So overall sounds like some attention needed to the focus magnet
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21st Feb 2021, 11:57 am | #135 |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
Yes, I agree. As for my comment on the tube rotation, it's actually incorrect. The geometry of the field inside the focusing magnet is cylindrical, so the possible interaction between the ion trap magnet and the focusing magnet if they're too close together does not depend on the tube rotation. Such interaction is still a bad thing though, and it's easy to see that if the ion trap magnet is too close to the focusing magnet, the two will stick together. In short: the ion trap magnet should be close to the base of the tube, and typically not more than 1 cm away from it.
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21st Feb 2021, 12:04 pm | #136 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
Just looking at this focus magnet , do I have a bit missing? When I got the set I noticed that the focus lever was missing , I subsequently found it floating about in the cabinet. Am I right that there should be a pin engaging with this helical cam track to move the focus thingy in and out?
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21st Feb 2021, 12:17 pm | #137 | |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
Quote:
Helder |
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21st Feb 2021, 12:18 pm | #138 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
Bingo
Now I understand how this magnet is supposed to work , I’m missing the cam follower that moves the barrel in and out. Managed to move it out a bit and put a bit of packing in to hold it Got a cracking picture now Any one got a picture of the missing bit so I can make a replacement |
21st Feb 2021, 12:23 pm | #139 | |
Hexode
Join Date: Sep 2019
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Re: My first telly TV22
Quote:
Helder |
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21st Feb 2021, 12:24 pm | #140 |
Pentode
Join Date: Jan 2021
Location: York, North Yorkshire, UK
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Re: My first telly TV22
Think I’ll reconnect the EY now and see how it looks
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