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Old 22nd Jan 2021, 1:24 am   #81
beery
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Default Re: My newly found Marconi 707

Hi Ed,
I've found this dual pot from the scrap set.
It is not actually a Morganite part, unlike the one in my HMV 905, but still an original EMI fitted part.
It is a little rust at the back, is a bit squeaky and the brass shaft is encrusted with rust from the knob and shaft adapter that were fitted to it.
However, both sections work OK electrically.

I would rather you don't ask for it until you have had a go at fixing the one in your set first. In any case if can get the original working it will probably be more reliable as your set has not seen the damp that my spare pot has seen.

Cheers
Andy
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Old 22nd Jan 2021, 2:22 am   #82
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Default Re: My newly found Marconi 707

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Hi Ed,
I've found this dual pot from the scrap set.
It is not actually a Morganite part, unlike the one in my HMV 905, but still an original EMI fitted part.
It is a little rust at the back, is a bit squeaky and the brass shaft is encrusted with rust from the knob and shaft adapter that were fitted to it.
However, both sections work OK electrically.

I would rather you don't ask for it until you have had a go at fixing the one in your set first. In any case if can get the original working it will probably be more reliable as your set has not seen the damp that my spare pot has seen.

Cheers
Andy
Hi Andy,

Spent this eve looking at this pot. As you can see the outer shaft has snapped along where the C clip would attach to. (As mentioned it was bent!) The surface area looks quite small to attempt to epoxy it - I wonít be able to re attach the C clip! Both Read good though.

I could attempt gluing the shaft but concerned it will have a weak point with the C clip tight around it.

What are your thoughts?

Would you have a shaft from a dud pot which could be sacrificed to repair this one!
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Old 22nd Jan 2021, 7:30 am   #83
tony brady
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Default Re: My newly found Marconi 707

Hi Ed, I've been following your restoration with great interest.

what I would do is drill both parts out on a lathe and fit a pin up the centre and use a little loctite. it will be far better than trying to glue it.

there seems to be a hole in the shaft already - does that go all the way through?

cheers
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Old 22nd Jan 2021, 8:52 am   #84
beery
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Default Re: My newly found Marconi 707

Hi Tony,
This is a dual concentric control, so the central hole is for the inner shaft. As such it can't be pinned . This is the sort of job that could be done with a lathe, but it would be tricky to make a new shaft, look how thin the metal is at the point where the break occurred.

Hi Ed,
It looks like that pot is the same type as my spare. Some of the pots EMI used were from the US and this might be one of those. I don't have many of this type and I certainly don't have any other dual pots of this type, except the one I mentioned earlier.

I think you definitely qualify for my spare! I'll send you PM.

Cheers
Andy
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Old 22nd Jan 2021, 8:56 am   #85
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Default Re: My newly found Marconi 707

Hi again Ed,
As I've never taken this make of dual pot apart before, I'm curious to know how you got the inner shaft out, or is that broken too?

Cheers
Andy
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Old 22nd Jan 2021, 10:16 am   #86
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Default Re: My newly found Marconi 707

Hi Tony,

As Andy has mentioned this is a dual pot, with the inner shaft hole being for one of the dual variable controls - so unfortunately I doubt I could drill this one out. A restorer friend suggested soldering it, but I donít know.

Hi Andy,

Thank you very much! I will respond now.

Iíve uploaded some photos here of the inner shaft and itís fixings. Appears to have another C clip with two brass(?) moulded points to hold the back cover on. I would dismantle further but donít want to destroy it more, as I think squashing those two little brass points is a one time thing, it wonít hold together afterwards!


Such a shame as itís actually perfectly good working order. Must have been bent up in its early life.
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Old 22nd Jan 2021, 10:17 am   #87
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Default Re: My newly found Marconi 707

Hereís a closer photo with light
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Old 22nd Jan 2021, 1:23 pm   #88
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Default Re: My newly found Marconi 707

To add to the collection, some photos I took (HMV 904).

In this case I had to make a new broader wiper, since the little washer had long come off the wiper V-lug and the track was badly scored.

Steve
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Old 25th Jan 2021, 10:28 am   #89
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Default Re: My newly found Marconi 707

Silver solder would make a solid join but it would fill the groove - is this the outer circlip? If it is you could make up a ring with fixing screws or even just glue a washer in place.
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Old 25th Jan 2021, 12:30 pm   #90
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Default Re: My newly found Marconi 707

I could have a go at turning one, but it will be a pain in the bum so only PM me the sizes if you can work out how to get the old one off the paxolin disk- is it riveted on, and could a replacement just glue on if a turned-down shoulder was provided on the shaft?

I don’t want to fit it for you - I have messed up someone’s stuff on here once, which was once too often.
M
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Old 27th Jan 2021, 6:08 pm   #91
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Default Re: My newly found Marconi 707

Thanks all for the comments about the pots. Andy has now sent me the spares one to fit so spent the afternoon doing this.

The radio portion of the set is now alive and kicking and receiving well, I thought I would move my attention onto the vision side of things.

I replaced the 2 domino capacitors feeding the grids of the timebase and proceeded to apply power. I was gifted with strong line whistle, and could hear the frame timebase purring away, but wasnít getting any raster on the tube.

R41 started burning up and eventually went open circuit. A quick power off, and a search for the shorted cap started. I had already replaced C23, but I think Iíve found the culprit. The shorted cap was behind the brightness/contrast pots, both C3 and 4 were both under 500 ohms, but the location on the schematic had nothing to do with R41 anyway. Thereís very few original caps left now, so even though the short is cleared Iíll be cautious. Iíll come back to this.

R41 is now replaced so now itís time to work on the TV side of things. Iíll post some updates when I get something on the tube!
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Old 27th Jan 2021, 6:23 pm   #92
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Smile Re: My newly found Marconi 707

To add about R41 going up in smoke, C64 and 65 were changed a while ago... who knows!
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Old 27th Jan 2021, 7:39 pm   #93
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Default Re: My newly found Marconi 707

I would be inclined to get the damaged one repaired as well, silver soldering will work but the circlip area would need to be turned off as would the other rough end. An aluminium rod can be inserted to prevent solder blocking the centre hole and keeping alignment,. then the circlip groove can be turned back. It would loose a couple of mm in length.
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Old 28th Jan 2021, 3:34 am   #94
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Default Re: My newly found Marconi 707

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I would be inclined to get the damaged one repaired as well, silver soldering will work but the circlip area would need to be turned off as would the other rough end. An aluminium rod can be inserted to prevent solder blocking the centre hole and keeping alignment,. then the circlip groove can be turned back. It would loose a couple of mm in length.

Hi Stephen, once Iím back in my London workshop, I might be able to rebuild the shaft, or defo give a good attempt at repairing it.
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Old 30th Jan 2021, 10:59 am   #95
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Default Re: My newly found Marconi 707

Hi Ed,
Now you should know that to be indoctrinated into the world of prewar tellies you have to be able to complete the following verse:-
"A mighty maze of mystic magic rays..."

This video of my set should help you answer that one and hopefully give you some encouragement. I know that these restorations can get a bit daunting once the scale of the work sets in. I was halfway through the restoration of my set when I learnt that we had a baby on the way! I'm sure you will get there in the end. The fact that you have already had first light from the tube that proves it is a good one means that you have a good basis for a lovely set.

Enjoy:-
https://youtu.be/b1vT0IVBQTg

Cheers
Andy

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Old 30th Jan 2021, 1:04 pm   #96
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Default Re: My newly found Marconi 707

Ecellent!

A mighty maze of mystic, magic rays
Is all about us in the blue,
And in sight and sound they trace
Living pictures out of space
To bring a new wonder to you
The busy world before you is unfurled -
Its songs, its tears and laughter, too.
One by one they play their parts
In this latest of the Arts
To bring new enchantment to you.
As by your fireside you sit,
The news will flit,
As on the silver screen.
And just for entertaining you
With something new
The stars will then be seen. So...
There's joy in store
The world is at your door -
It's here for everyone to view
Conjured up in sound and sight
By the magic rays of light
That bring Television to you.

But not the only television song to learn. There's also "Here's Looking at You" although the recordings of it are a bit fragmented.

ďHere's looking at you
From out of the blue
Don't make a fuss
Just settle down and look at us...Ē
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Old 30th Jan 2021, 11:49 pm   #97
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Default Re: My newly found Marconi 707

These songs drive home the special 'magic', 'thrill', and 'wonder' aspects of television in the 1930s - which I think still motivate restorers today!

Steve
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Old 31st Jan 2021, 8:51 am   #98
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Default Re: My newly found Marconi 707

Spot-on Steve.

Peter
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Old 31st Jan 2021, 3:35 pm   #99
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Default Re: My newly found Marconi 707

A fragmented "Here's Looking at You"

https://youtu.be/GMVY91qHBdg
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Old 31st Jan 2021, 6:59 pm   #100
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Default Re: My newly found Marconi 707

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A fragmented "Here's Looking at You"

https://youtu.be/GMVY91qHBdg
The operator at the console taps one of the big meters with his fingers, I wonder if i's the famous gallons per minute gauge?
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