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Old 20th Feb 2021, 9:03 pm   #121
Helder Crespo
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Default Re: My first telly TV22

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Originally Posted by Travellingwave View Post
Why would contrast affect picture size? It’s way back from the time base circuits? Anyway will have a look tommorrow
Some info on this from post #7: https://www.vintage-radio.net/forum/...d.php?t=143058
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Old 20th Feb 2021, 10:08 pm   #122
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Default 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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Old 20th Feb 2021, 10:23 pm   #123
Helder Crespo
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Default Re: My first telly TV22

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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
Hi Andy
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

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Old 20th Feb 2021, 11:55 pm   #124
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Default 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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Old 21st Feb 2021, 1:10 am   #125
Helder Crespo
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Default Re: My first telly TV22

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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
Hi Andy. Many thanks for your detailed explanation. I hadn't thought about vision on sound and sound on vision. I will test the attenuators again next time I'm in London as one of the limitations I found when adjusting the oscillator + rf + aerial coils was that best resolution resulted in sound on vision, so the attenuated signal may give me a bit more margin.
Cheers
Helder

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Old 21st Feb 2021, 9:47 am   #126
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Default 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?
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Old 21st Feb 2021, 9:49 am   #127
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Default 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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Old 21st Feb 2021, 9:56 am   #128
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Default Re: My first telly TV22

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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.
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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Old 21st Feb 2021, 10:05 am   #129
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Default 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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Old 21st Feb 2021, 10:06 am   #130
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Default Re: My first telly TV22

Have got an attenuator to collect from local DIY shed
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Old 21st Feb 2021, 10:23 am   #131
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Default Re: My first telly TV22

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Yes , to be honest focus lever doesnít seem to have a huge effect , itís also quite stiff , beam centering controls seem to work ok though
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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Old 21st Feb 2021, 10:29 am   #132
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Default Re: My first telly TV22

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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
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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Old 21st Feb 2021, 10:36 am   #133
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Default Re: My first telly TV22

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Yes , to be honest focus lever doesnít seem to have a huge effect , itís also quite stiff , beam centering controls seem to work ok though
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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Old 21st Feb 2021, 10:46 am   #134
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Default 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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Old 21st Feb 2021, 10:57 am   #135
Helder Crespo
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Default Re: My first telly TV22

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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
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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Old 21st Feb 2021, 11:04 am   #136
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Default 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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Old 21st Feb 2021, 11:17 am   #137
Helder Crespo
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Default Re: My first telly TV22

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Originally Posted by Travellingwave View Post
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?
Yes, totally! no wonder you can't get a focus. See attached photo.
Helder
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Old 21st Feb 2021, 11:18 am   #138
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Default Re: My first telly TV22

Bingo
Now I understand how this magnet is supposed to work , Iím 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
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Old 21st Feb 2021, 11:23 am   #139
Helder Crespo
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Default Re: My first telly TV22

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Originally Posted by Travellingwave View Post
Bingo
Now I understand how this magnet is supposed to work , Iím 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
Bingo! Well done! Here are some photos.
Helder
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Old 21st Feb 2021, 11:24 am   #140
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Default Re: My first telly TV22

Think I’ll reconnect the EY now and see how it looks
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