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Old 1st Jul 2020, 3:05 pm   #41
Welsh Anorak
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Default Re: Marconi 1400 birthday present

How is the boost voltage? Also is the PL504 getting hotter than expected?
Of course someone could have put the wrong tripler in - it happens!
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Old 1st Jul 2020, 11:11 pm   #42
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Default Re: Marconi 1400 birthday present

If the wrong EHT tray has been fitted it would likely be a doubler which would produce less EHT resulting in excess width. Doubler was used with 16/17" models on the 1400, also 20" and below on the 1500.

1500 tripler in a 1400 and vice versa is not a problem other than the physical orientation, still produces 20kV. 950 tripler is fully compatible also.

Usually an easy problem to resolve and I've nothing extra to add to the other contributions, good luck anyway.

John.
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Old 2nd Jul 2020, 1:05 am   #43
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Default Re: Marconi 1400 birthday present

I havnt had time to do anything tonight .
The EHT tray is the open type clearly showing 5 sticks. I do have spare ones but donít know if they are correct as they are potted with no markings .im sure there is a way to tell Andy
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Old 2nd Jul 2020, 9:49 am   #44
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Default Re: Marconi 1400 birthday present

Quote:
Originally Posted by jayceebee View Post
If the wrong EHT tray has been fitted it would likely be a doubler which would produce less EHT resulting in excess width. Doubler was used with 16/17" models on the 1400, also 20" and below on the 1500.

1500 tripler in a 1400 and vice versa is not a problem other than the physical orientation, still produces 20kV. 950 tripler is fully compatible also.

Usually an easy problem to resolve and I've nothing extra to add to the other contributions, good luck anyway.

John.
Not quite true about the 950. The original is a half wave rectifier type.
Correct if referring to the 950mkII of course though, at least the 20kv 5-stick version.

1500 trays fit to the 1400s without any problems, but the reverse doesn't apply as the tray will be uppermount and too close to the PL504.
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Old 2nd Jul 2020, 9:54 am   #45
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Default Re: Marconi 1400 birthday present

Quote:
Originally Posted by bionicmerlin View Post
I havnt had time to do anything tonight .
The EHT tray is the open type clearly showing 5 sticks. I do have spare ones but donít know if they are correct as they are potted with no markings .im sure there is a way to tell Andy
A 19" or 20" 1400 requires a 3-stick EHT tray. A 5-stick one will give too high EHT which could explain your width problem!

I'd fit a 3-stick tray before doing anything else.
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Old 2nd Jul 2020, 11:11 am   #46
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Default Re: Marconi 1400 birthday present

Hi Brian, you’re correct about the 950mkII tripler but the 19 and 20” 1400s should definitely have a five stick unit fitted. On the 1500 it was only 24” models that were fitted with triplers.

List of tray and transformer combinations here.

John.

Last edited by jayceebee; 2nd Jul 2020 at 11:19 am. Reason: Added link
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Old 2nd Jul 2020, 12:13 pm   #47
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Default Re: Marconi 1400 birthday present

Gosh, in all these years I never knew that! Perhaps because I've only worked on large screen versions, yet plenty of 20" 1500s.

My 16" Courier III has a 3-stick unit, presumably because it's 16" rather than 19" or 20".

Talk about learning something new every day!
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Old 2nd Jul 2020, 12:41 pm   #48
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Default Re: Marconi 1400 birthday present

If an incorrect tray is fitted the results are dramatic. Either masses of width and height with low EHT or an over bright small picture with excessive EHT. J.
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Old 5th Jul 2020, 2:40 am   #49
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Default Re: Marconi 1400 birthday present

Well I have managed to make some improvement. .i have tried fitting a new 1500 EHT tray.the results on 405 are good. . On 625 itís Better but not quite there.
I was reading an article by John law going along with what Nick was saying with the VDR as a possible problem. Also he said it can fail if C113 goes faulty. (100pf 2KV pulse) not that I have one to hand.
I still have poor contrast on 405 I have checked the pot and changed a couple resistors but no joy. Contrast is very good on 625.
I got a couple pictures . I also replaced R70 as Dazzlevision recommended.
Andy
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Old 5th Jul 2020, 9:16 pm   #50
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Default Re: Marconi 1400 birthday present

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Originally Posted by Focus Diode View Post
1500 trays fit to the 1400s without any problems, but the reverse doesn't apply as the tray will be uppermount and too close to the PL504.
Ugh, I got that horribly wrong didn't I? I should have said 1400 triplers fit in 1500s but not vice versa. The 1400 type fits horizontally in both 1400 and 1500 models. The 1500 one fits vertically, downwards in the 1500 and upwards in the 1400.

Think my confusion stemed from fitting a sealed tray labelled, "1500 large screen" to a 1400 that did fit horizontally to the Lopt, as it would have done on a 1500.

My apologies for this incorrect information.

The results on your set looks excellent, but it's clear you've fitted a vertical fitting 1500 tray.

While, of course, being electrically identical the mounting is a cause for concern. The heat from the PL504 will soon burn through the insulation unfortunately.
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Old 5th Jul 2020, 10:20 pm   #51
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Default Re: Marconi 1400 birthday present

Focus diode.
Itís not ideal how it is but it works. Iím sure I can improve on it to keep the wire away from the valve. 1400 trays I find are hard to come by on the other hand the 1500 trays do turn up at radio rallys etc . Same with the droppers.
Iím still thinking the VDR might be worth trying and changing C113
Can anyone advise if C113 is special ,will a 100pf 2KV do . Itísays in the service sheet itís a pulse . I donít have anything to hand anyway.
Still trying to work out contrast problem on 405 Andy
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Old 5th Jul 2020, 11:19 pm   #52
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Default Re: Marconi 1400 birthday present

Hi Andy,
Still looks like you need just a shade more width! I normally find to get a fairly round circle on the test card, I need to pull the width out so the castellations are pretty much just off the screen. So I would probably want a good 1/2 inch extra each side! I assume the width you have is with the control at maximum?

The width stabilisation circuit seems to be much the same as both my KB VC4 & Sobell 1000. The VDR in both these sets has a cream body with a blue & black splodge. Is that the same as the 1400?

I did find the data on these VDR's- I'll post a link if I can locate it again.

I'm sure both the relevant caps on the above sets (equivalent to C113) are red tubular things about an inch long. One lead out wire comes from the middle which makes them quite distinctive. I've never seen any other caps like them, but they often appear in line stages so I assume they would be 'pulse capacitors'. I'm sure they are rated at 12KV.

When you say low contrast on 405, is the picture OK but just lacking in contrast or smeary and poorly defined?

The contrast controls vary the fixed bias on the AGC line which in turn varies the gain of the 1st IF amplifier, V3 (and the tuners). It's very high impedance so is very sensitive to leaky caps. C13,C15,C16 could all cause problems.

Most of it is common to both 405 & 625 however. Does the local/ distant control have any effect? Might also be worth trying another EF183 as this could be low gain. It might manage just enough signal for 625, but run out of steam on 405.

The output of the 625 tuner is amplified by the 405 tuner, so V3 has to amplify less on 625 than it does on 405 to give the same overall picture contrast.

I'll see if I can find the VDR data.

Found it! https://www.vintage-radio.net/forum/...80&postcount=8. The second one down in the table E298ZZ/06 has the black & blue markings.

All the best
Nick

Last edited by 1100 man; 5th Jul 2020 at 11:29 pm. Reason: more text added
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Old 6th Jul 2020, 9:20 am   #53
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Default Re: Marconi 1400 birthday present

Hello Andy. I have the correct capacitors 220pf third harmonic tuning, 100pf in the stabilization circuit and the rod VDR [Beige end dot] The capacitors are the later I.F.D. disc type.
I have plenty spare so feel free to let me have your address via PM and I will put them in the post FOC. John.
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Old 6th Jul 2020, 1:59 pm   #54
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Default Re: Marconi 1400 birthday present

John . Thanks for your very kind offer I will PM you now.
Nick . The capacitors you mentioned have all been changed. I have also changed the valve you suggested. I got a very minor improvement.
Now the big difference . The local distance control as you also mentioned. It was fully turned to one end. I fully turned it the opposite end and I now have a good acceptable contact on 405 . It hasnít made any change on 625 . I know pots idealy shouldnít be fully one end but it works.
I will wait to i get these parts from John.
Thank you both and everyone who has helped me so far. Andy
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Old 6th Jul 2020, 4:09 pm   #55
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Default Re: Marconi 1400 birthday present

The local/distant control was only operative on VHF (405) reception - and on VHF/625 communal aerial relay systems.

Its purpose was to set the point at which the vision AGC system started to reduce the gain of the RF amplifier stage in the tuner, rather than the gain of the vision IF amplifier. This was to ensure an optimum signal to noise ratio.

This was set at the factory and adjustment was only necessary when the aerial signals were very strong. Otherwise, on typical aerial signal strengths, you would set it to the point at which the picture just began to show "noise/snow/grain" and then back it off slightly.

In the Thorn 1400 chassis, there is a high value resistor connected to the wiper of each contrast control. It is not unknown for these to go very high value (or even open-circuit), causing very low contrast - with the contrast control having no, or little effect.
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Old 6th Jul 2020, 4:27 pm   #56
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Default Re: Marconi 1400 birthday present

Had that one a few times and not just on the 1400. J.
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Old 7th Jul 2020, 12:45 pm   #57
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Default Re: Marconi 1400 birthday present

When Tag 43 is moved to Tag 44, marked 625 VHF, the local distance control comes into operation on 625 UHF as well. Both 405 and 625 contrast controls function as well.

The set will still work on 405 VHF if the solenoid is disconnected or if a switch is fitted to it, allowing a choice of 405 or 625 VHF.
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Old 10th Jul 2020, 2:12 am   #58
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Default Re: Marconi 1400 birthday present

Update so far.
I have now fitted the parts that John kindly sent me (Thank you). As far as I’m concerned this has sorted the width problem. I will do a little tweaking later as I think I can improve on the picture.i will for curiosity try the old EHT tray again . I will also double check some of the resistors that has been mentioned.
I’m having a bit of distortion and pulling on the picture on 625 switching on from cold that corrects its self after about 30 seconds. I’m thinking it could be the tuner as I haven't got round to cleaning the grease inside the tuner as I was advised to.
Photo on 625 with improved width. Andy
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Old 10th Jul 2020, 10:25 am   #59
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Default Re: Marconi 1400 birthday present

On a 5:4 aspect ratio CRT, such as this 19" one, you wouldn't normally see the left and right hand side test card castellations, as a degree of horizontal overscan is needed in order to make the test card circle truly circular. I suspect there is still a problem in the line timebase.

There is also some video foldover on the left hand side castellation area.

Even so, you have made good progress.
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Old 10th Jul 2020, 8:50 pm   #60
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Default Re: Marconi 1400 birthday present

Thanks Dazzlevision. Iím taking on board what your saying. I will have another look . Not sure I can go much further but I will try Andy
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