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Old 21st Feb 2018, 8:45 pm   #21
jayceebee
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Default Re: Marconi 4816 1590 survivor!

Quote:
Originally Posted by Heatercathodeshort View Post
The chassis is interesting, almost a cross between the 980 and a 1500.
And the 960 also, note the capacitor dropper for the heaters.

John.
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Old 21st Feb 2018, 10:01 pm   #22
Heatercathodeshort
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Default Re: Marconi 4816 1590 survivor!

It's a pity that very high quality capacitors were not available years earlier. That would have eliminated the troublesome mains dropper but would have reduced the income of service engineers. I loved droppers!

As I have mentioned before. The main reason for tube failure was down to the preset LT supply pot. It was rated at 220ohm but would creep up in value to over 2k resulting in a 15v rail before hum instigated a service call. By then it was too late. I used to fit a ceramic high quality pot. Problem solved. John.
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Old 24th Feb 2018, 8:06 pm   #23
slidertogrid
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Default Re: Marconi 4816 1590 survivor!

The parts arrived today from Dave (Dazzlevision) that will make the set complete and working fully again.
I am going to get it back on the bench and fit the parts as soon as I have finished the PYE tuner I am repairing for a friend.
I am really looking forward to the little Marconi working properly again after it's near miss.
I would love to take it on a picnic in the summer just as an excuse to run it on a car battery but I will need a digi box and a good aerial. I may get a few funny looks putting up an aerial in the middle of a field...
I only ever saw one of the hybrid sets back in the day they must have been a very uncommon model. It was a set I bought to resell and I was quite disappointed when I took the back off and found it was "an old valve chassis"!
How things have changed I would love one now!
Thanks Dave you are a star and you have made an old telly very happy!

Rich.
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Old 5th Mar 2018, 10:23 pm   #24
slidertogrid
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Default Re: Marconi 4816 1590 survivor!

I had a bit of time to spare today so I thought I would fit the parts to the Marconi. I fitted the 12 volt socket replaced the on off volume control and knob.
The knob on my set looks like it came from a transistor radio it originally came from a pot with a splined shaft. Someone had sawed slots in it to fit the flat on the control on the TV.
Once the set was back together and working I decided to dismantle the original control to see what damage had been done.
The switch contacts are blown to bits, the track that formed part of the switch was also fairly blasted. no wonder the control crunched and crackled!
Some pictures...

Rich.
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Old 6th Mar 2018, 9:14 am   #25
mark pirate
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Default Re: Marconi 4816 1590 survivor!

I bet the original owner must have jumped a foot in the air when he switched it on
I have never seen a pot that badly burned up, I reckon there was quite a bright flash to go along with the bang.
Nice to see it returned to working order, now bearing no scars from it's ordeal.

Mark
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Old 6th Mar 2018, 6:27 pm   #26
dazzlevision
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Default Re: Marconi 4816 1590 survivor!

Glad to see it back in original condition!

I'd check the stabilised LT voltage rail, which can rise due to component drift. If it is high for a long period, the CRT will become low emission.
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