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Old 27th Jul 2020, 1:04 am   #61
bionicmerlin
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Default Re: Marconi 1400 birthday present

Finally I have got back to the set. I have unsoldered the tuner contacts and cleaned the old grease off and got that working as suggested.
I still occasionally get picture distortion on 625 like a sort of twisting and pulling. It sorts it’s self out within 30 seconds then another time it won’t do it at all.
I also find the focus perfect on 625 but not so good on 405. The focus control does nothing. I have checked the pot and resistors in line but they are fine.
I think I have probably gone as far as I can go with my limited knowledge.
The tv well not 100% is certainly good enough for me.
Thanks everyone who helped me and john for supplying the parts I did not have Andy
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Old 27th Jul 2020, 1:18 pm   #62
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Default Re: Marconi 1400 birthday present

The feed resistor to the focus control has probably gone o/c. A very common fault on the 1400 and 1500s.
It's unusual for it to do absolutely nothing when the feed resistor is intact.
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Old 27th Jul 2020, 11:25 pm   #63
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Default Re: Marconi 1400 birthday present

Thank you for the advice. I’m sure I have checked but will double check . Andy
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Old 2nd Aug 2020, 7:36 pm   #64
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Default Re: Marconi 1400 birthday present

I have been using the set over the last few days. The focus is still not working despite changing / checking resistors as per advice. Having said that it’s improved through use.
New problem . After being on for about an hour and a half the replacement tripler failed..
It was red hot and there is blister on the back. In my mind it must have been faulty when I put it in . New old stock..or I think less likely it’s not the correct one and that’s why it failed. (For a 1500)
I wonder what others think as These are getting hard to come by I don’t want to use up my stock damaging another one if it’s my fault. Photo of blister mark.
Andy
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Old 2nd Aug 2020, 9:03 pm   #65
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Default Re: Marconi 1400 birthday present

Hi Andy,
I suspect it's just bad luck rather than being the wrong tripler. Don't forget, even though it was new old stock, it's still 30 odd years old and could have suffered moisture ingress in exactly the same way as capacitors do.

The only difference between different triplers is the number of stages of multiplication giving different EHT voltages. As the EHT was not radically wrong, I can't believe it was the wrong tripler.

I've never found the focus potential on these sort of narrow neck 110 degree tubes makes much difference. There is not much effect on most of the sets I have played with. Maybe when the tube is new it has more effect?

With regard to the softer picture on 405, that looks like more of a tuning issue to me. The actual focus of the tube can't change between 405 & 625. What happens when you adjust the fine tuning ring on the 405 tuner? You should be able to get a much sharper picture on 405 than that!

Apart from that issue, the end results look pretty good!

All the best
Nick
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Old 2nd Aug 2020, 10:54 pm   #66
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Default Re: Marconi 1400 birthday present

Nick .
Thanks for your advice. I was thinking I was unlucky with the tripler just wanted a second option from someone who knows more than me. (So that’s not difficult.)You could be right about the fine tuning on 405. The picture did get better and it maybe me who did slightly move the fine tuning without knowing. It’s at its best setting now..
Thanks again Andy
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Old 2nd Aug 2020, 11:44 pm   #67
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Default Re: Marconi 1400 birthday present

Check to see if the voltage varies on the focus pin 4 of the tube. It may be worth having a look at the tube base especially if it is blue plastic. This often cracks allowing the ring trap to work loose and short out pins of the tube to earth.
It was a very common fault often shorting out the heater or A1 supply. John.
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Old 4th Aug 2020, 11:55 am   #68
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Default Re: Marconi 1400 birthday present

John
I have looked at the tube base and it’s fine. As a double check I went round the pins with a meter. That’s good information for future sets. Also the pins on the tube and socket are not damaged
I tested the voltage on pin 4. When I turn the focus pot. It measures between zero and 360 volts. But does absolutely nothing.
It’s acceptable as it is though.
One other thing I get about 30% of the time Is on cold switch on on 625.is for about 30 seconds the picture is distorted and snakes getting worse .then settles down and is then fine.
Thanks Andy
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Old 4th Aug 2020, 1:51 pm   #69
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Default Re: Marconi 1400 birthday present

Just bad luck with the tripler, and it looks like an aftermarket job, remo or the like.
Greg.
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Old 4th Aug 2020, 6:10 pm   #70
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Default Re: Marconi 1400 birthday present

Just to brighten your tripler failure I must tell you the tale about repeated tripler failure on a Thorn 950 MK2.
It was a long time ago involving an elderly, well not exactly elderly but everyone over 30 seems ancient when your 20! They lived a few doors away from Wimbledon Theatre.

I was called to look at a Ferguson 950 Mk 2, the 20KV version with the five stick tripler.
The tripler was faulty and a replacement new Thorn tripler was duly fitted. Everyone was happy.

Three days later I had a service call to report that the picture had vanished and the set had a certain smell about it. Upon calling the open type tripler had failed again. I checked everything but could find no reason for this. I fitted another tripler FOC from the same batch I had received from BRC PO Box 121 about a week before. Everything was fine and we left on a good friendly basis.

You know what I'm about to write....About another three weeks later, yes another service call to report this time that the picture had vanished and the whole house smelt of Pxx.

This time it was a stink bomb special. I rang the bell and waited for the customer to answer. I could smell the stink in the porch! They led me to the offending cause of the stink and yes of course the tripler had failed in a spectacular way. It had really put a top hat on it this time. Their big black Labrador looked at me as if to say, 'At first they blamed that stink on me!'

The lady of the house as only those incredible types that survived the blitz in WW2 could, described the sorry saga, the way the stink had crept through the entire house and had actually seeped into the street!

She ended the tale with the best finale ever! 'It stank the whole house out, even our bedroom. The smell of Pxx put us off and we couldn't 'av no relations..'

A third tripler was fitted from yet another delivery from BRC but this time there was hope! They were the new solid type and after many months the 950 was still working without any more tripler failures.

The open type on the whole were not that unreliable so I suppose I may have got hold of a bad batch but they were all replaced by that fantastic service organisation known as BRC together with the remaining ones from that unfortunate first delivery.

Does anyone remember the EHT 'Trays' trapped by their leads in the back doors of the Ford Anglia vans used by DER?

memories never forgotten. John.
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Old 4th Aug 2020, 8:17 pm   #71
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Default Re: Marconi 1400 birthday present

Thanks john for sharing your story .what some happy fun times you had. It just wouldn’t happen today. I have gone back and looked at a good few threads of your days in the trade ,again great story’s. You should write a book Andy
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Old 5th Aug 2020, 8:06 pm   #72
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Default Re: Marconi 1400 birthday present

You've no doubt done this already, the boost voltage should be checked for, if my memory serves me correctly, no more than 720V on 625-lines.

A case of repeated tripler failure was once traced to the width control being set at maximum, this resulting in excessive boost voltage. It was obvious over set to mask a decreasing width problem.

If you have an "open" type tray to hand it's possible to replace the individual stick rectifiers with mini EHT diodes, can't recall what type, perhaps someone could advise?
They are small enough to fit inside the the thin rectifier sticks.
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Old 5th Aug 2020, 8:54 pm   #73
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Default Re: Marconi 1400 birthday present

Quote:
Originally Posted by Focus Diode View Post
You've no doubt done this already, the boost voltage should be checked for, if my memory serves me correctly, no more than 720V on 625-lines.
That's a very good point. I know Andy has been having width problems -as in there isn't enough of it! So it's possible the width control is at maximum to compensate.

Quote:
If you have an "open" type tray to hand it's possible to replace the individual stick rectifiers with mini EHT diodes, can't recall what type, perhaps someone could advise?
They are small enough to fit inside the the thin rectifier sticks.
The Selenium sticks will have quite a significant resistance, so I would imagine that replacing them with diodes would give much higher EHT.

It's a project I've been meaning to do for a while- rebuild a Thorn 2000 tripler with BY182 diodes and see if it actually does give high EHT. I think the whole thing would have to be potted to prevent arcing across the small diode body.

I think actually it's the capacitors in these units that cause more problems than the sticks! Certainly that's what's failed in my 2000 tripler.

Cheers
Nick
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Old 5th Aug 2020, 11:32 pm   #74
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Default Re: Marconi 1400 birthday present

Yes I do have the width set at max. It’s more of a problem on 625 .
How do I check the boost voltage my inexperience is kicking in now.
Thanks Andy
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Old 9th Aug 2020, 9:12 am   #75
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Default Re: Marconi 1400 birthday present

The boost capacitor is C105. The voltage is measured at this point. Adjusting the width control varies the voltage.
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Old 9th Aug 2020, 5:52 pm   #76
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Default Re: Marconi 1400 birthday present

The reason the picture is not so highly contrasted on the 1400 series is the use of the Mazda 6F28 video output valve. Thorn took over Mazda and no longer wanted to use Mullard valves. The earlier 900/950/970 employed the PFL200 with it's incredible gm of 21m/a per volt.
This compared with the much lower gain, 12.5 m/a per volt for the 6F28 results in a much lower video amplifier performance. It's OK but could really do with a bit of spare to play with. The advantage is the 6F28 is a very reliable valve, certainly when you compare it to early versions of the PFL200.

To eliminate sync crushing on 625, remove R44 [10K] and C40 [.1uf] and replace with a single .003uf cap. This will allow you to set the contrast a little higher without the wobbles! This mod calmed down many a 1400 supplied with a good UHF signal in Wimbledon. John.

There is too much sync coupling on UHF with the original components.
Regards, John.
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Old 10th Aug 2020, 1:13 am   #77
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Default Re: Marconi 1400 birthday present

Thanks both of you for the advice. I will check the boost voltage. That diagram makes it obvious It I tend to think I just had a bad trippier. I have been using a open type one out of a scrap set . After a hour it’s hardly warm.
John thanks for your info on the valves I will do that mod you suggested as soon as I get a chance Andy
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