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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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14th Sep 2019, 12:03 pm | #21 |
Dekatron
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Re: Yet Another Bush TV22
Thanks to you both. I only had a 0.47uF so that's what's in place of the 0.75uF.
The only thing is that having it in or out of circuit didn't appear to alter my rippling frame. I did check the 2uF on the scan coils but it appears leak free. I got a small improvement in positioning by removing the scan coils and bending the frame ones slightly. Peter |
14th Sep 2019, 12:19 pm | #22 |
Octode
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Location: Stevenage, Herts. UK.
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Re: Yet Another Bush TV22
If you have one to hand try temporarily replacing the 2u electrolytic with a nonpolarised polyester or similar.
Also do add 0.22uf in parallel with your 0.47uf to get full benefit of hum reduction. Note the hum reduction caps should be rated at least 500VDC and preferably more. |
14th Sep 2019, 12:42 pm | #23 |
Dekatron
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Re: Yet Another Bush TV22
I did look at the possibility of an electrolytic but saw that it would be reverse polarised on part of the cycle so I fitted a non polar 400 volt cap. I've now added a couple of 0.1 uF 1000v caps and I must confess that it does look much better.
I think you and David have just saved me from further fruitless going around the houses. Very many thanks to you both. Peter |
14th Sep 2019, 12:44 pm | #24 |
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Re: Yet Another Bush TV22
It's possible to restuff the 0.75mfd capacitor with RS components class X 300VAC 0.68uF and 0.068uF capacitors. Connected in parallel you've almost got the exact value.
DFWB. |
14th Sep 2019, 12:56 pm | #25 |
Octode
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Re: Yet Another Bush TV22
This thread has the info on why the hum reduction cap has to be absolute minimum 465v DC rated.
https://www.vintage-radio.net/forum/...d.php?t=143583 |
14th Sep 2019, 1:38 pm | #26 |
Dekatron
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Re: Yet Another Bush TV22
The DC rating of a 300VAC class X capacitor will be much higher.
DFWB. |
14th Sep 2019, 2:34 pm | #27 |
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Re: Yet Another Bush TV22
Just connecting my 1M scope probe on various parts of the frame oscillator I was surprised at the substantial increase in scan amplitude it produced. For example on the anode of V15b.
I also found that increasing the value of R53 from 220k up to 350k gave a similar scan amplitude increase and I think gave a benefit in the ratio of HT ripple to scan amplitude. I'm still not out of the woods yet but it has been good to see where others have been with this. I have pretty rubbish line linearity still. Probably not helped by me hand rewinding the linearity transformer. If you ignore the aliasing brightness and just look at the scan ripple you can see my current state in this short video. Note the lethal collection of capacitors to the right of the screen. Peter |
14th Sep 2019, 3:51 pm | #28 |
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Re: Yet Another Bush TV22
Picture of the original 0.75mfd 250VAC capacitor.
DFWB. |
14th Sep 2019, 4:31 pm | #29 |
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Re: Yet Another Bush TV22
I have my original TCC just the same as yours.
Awaiting stuffing. Peter |
15th Sep 2019, 1:31 pm | #30 | |
Dekatron
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Re: Yet Another Bush TV22
Quote:
I still need sort out the rippling frame. Peter |
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15th Sep 2019, 1:54 pm | #31 | |
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Re: Yet Another Bush TV22
Quote:
Also if the job calls for a theoretical capacitor of around 500V, these days I simply fit a 1000V polyester or polypropylene part, because it allows for potential variation in manufacturing quality and tolerances and perhaps the more aggressive environmental conditions inside hot valve TV sets. This is also why I use the RS components silicone rubber insulated harsh environment wire in these sets. Also modern capacitors are so much smaller, a 1000v part will probably be the same size as a 500V vintage capacitor. If space was an issue, obviously a 600V rated one would suffice. But in many ways it is better to know it will be definitely ok and you won't have to go back later to replace the same part. |
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15th Sep 2019, 4:27 pm | #32 |
Dekatron
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Re: Yet Another Bush TV22
Hi Hugo,
Can you recall your source? "I replaced the one in my set with a 0.68uF 1kV rated polypropylene type." Peter |
15th Sep 2019, 10:01 pm | #33 |
Dekatron
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Re: Yet Another Bush TV22
Checking the effect on the HT ripple the 0.74uF makes a substantial reduction but curiously it makes virtually no difference to the ripple on the frame.
Peter |
15th Sep 2019, 10:48 pm | #34 | |
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Re: Yet Another Bush TV22
Quote:
A quick search on the RS site shows a perfectly satisfactory part for the task, cheap enough too, 850V is fine: https://au.rs-online.com/web/p/polyp...itors/6842232/ I think this must have been the actual 1000V part I used from Element 14: https://au.element14.com/cornell-dub...citor%200.68uF I also replaced the electrolytic yoke capacitor with a non-electrolytic as shown in the photo. Also you can see the wiring leading to the yoke is the RS silicone rubber type and I put some white fiberglass sleeving over it as well. Its darn hot inside these TV's. Especially when you run them here with a 30 DegC ambient temperature ! Last edited by Argus25; 15th Sep 2019 at 11:01 pm. |
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15th Sep 2019, 11:10 pm | #35 |
Dekatron
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Re: Yet Another Bush TV22
Thanks Hugo, those look good.
Peter |
16th Sep 2019, 7:43 am | #36 |
Heptode
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Location: Ware, Hertfordshire, UK.
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Re: Yet Another Bush TV22
Hi Peter,
looks good so far. Now I know from its circuit position, C63 should not effect the frame timebase, it is worth checking anyway as I usually find it to be low in value, which is a supprise as the dual canned C61 and C62 are usually fine. I do have a spare for C61/C62 and a linearity coil, but won't be able to get to them before Christmass. Another thing you could try is replacing the PZ30, just in case it is a bit leaky. I have had field hum from ECL80 valves, you have swapped them, with each other or did you try a spare? I have known two valves to have similar problems if they have been well used (I know this is unlikley though). Cheers Andy
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16th Sep 2019, 9:04 am | #37 |
Dekatron
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Re: Yet Another Bush TV22
Thanks for those suggestions Andy. You are quite right about R63 mine reads 45 ohms instead of the 38 ohms intended and I did parallel it up to give 35 ohms but didn't see any change in the frame ripple. I also tried messing with C60 and it definitely makes a very significant reduction in the HT ripple at the frame timebase. The thing I can't understand is that I don't see any significant change in the frame ripple regardless of whether the HT ripple is reduced or not! Perhaps that does point to heater "crosstalk" even with grounded cathodes.
I have a lot of ECL80s and lots are duds that I should discard but I'll try again for a good swap. I haven't tried swapping the PZ30 but I will do. Thanks, Peter |
16th Sep 2019, 9:44 am | #38 | |
Heptode
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Re: Yet Another Bush TV22
Quote:
I meant C63 (although R63 was a good thing to check). C63 is the metal canned 16uF electrolytic located on the underside of the chassis, near the front. If it is leaky it could be dragging the HT down and increasing the ripple. Yes, ECL80s seem to multiply. I've got thousands of valves, but most are used Mullard TV types. Every time I need an MOV, Mazda, Cossor or Brimar, I have to get my wallet out... Cheers Andy
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16th Sep 2019, 10:07 am | #39 |
Dekatron
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Re: Yet Another Bush TV22
Hi Peter,
How did you degauss the scanning coils? I remember the method used to degauss the Pye LV20 scan coils was to apply the rather brutish method of hitting the coils with a burst of HT. Bangs and sparks but it solved the problem. An alternative method is to use a fully charged capacitor. Sound on vision and vision on sound is often caused by the RF deck HT supply decoupling capacitor having gone low capacity. The 16mfd capacitor is located on the main chassis near the five pin socket. DFWB. |
16th Sep 2019, 10:36 am | #40 |
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Re: Yet Another Bush TV22
Hi Andy, Oops, sorry Andy. Can't read! Yes, I had renewed all three C61,62,63. The ripple on C63 is huge so I also replaced all screen decouplers in RF deck and C8 and 17.
I just tried 6 different ECL80s this morning. Four were low emission and two usable but without exception they all displayed the frame ripple. Just tried swapping the PZ30 but still no change. Thanks, Peter Last edited by peter_scott; 16th Sep 2019 at 10:46 am. |