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Old 22nd Nov 2008, 10:52 pm   #1
Alan Stepney
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Default Spot wobble

Does anyone recall which was the last set to employ spot wobble?

The last one I can remember working on had a toggle switch on the back to switch it in or out, but I dont remember the make or model.
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Old 23rd Nov 2008, 12:25 am   #2
dazzlevision
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Default Re: Spot wobble

Hello,

I think the most recent that I can recall is a KB early dual standard (VC1 chassis) and some models featured a "line eliminator" circuit.

Regards,

Dazzlevision
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Old 23rd Nov 2008, 8:55 am   #3
Mike Phelan
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Default Re: Spot wobble

Was the one with the switch an Ekco? I'm sure they started that idea.
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Old 23rd Nov 2008, 9:02 am   #4
dazzlevision
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Default Re: Spot wobble

Yes Mike, Ekco fitted spot wobble to several of their sets in the 1950s. There was a toggle switch above the CRT "bulge" on the back cover. The circuit involved a small sub chassis fixed to the CRT support brackets, using a single Mazda valve (8-pin base) and a coil around the CRT neck. The valve formed an oscillator working in the low MHz region (IIRC).

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Old 23rd Nov 2008, 10:25 am   #5
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Default Re: Spot wobble

Yes, I had an Ekco with it. The effect wasn't good. I'm surprised that they went to the expense of including it. I think it was the T231, same as in Petertheorgan's recent thread.

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Old 23rd Nov 2008, 10:43 am   #6
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Default Re: Spot wobble

The trick with spot wobble was the setting up and coil position. The idea was to elongate the spot in a vertical direction very slightly. There was a preset amplitude pot on the Ekco sub chassis [6L18 triode]that had to be adjusted very carefully to obtain this. The problem was patterning on the screen due to radiation from the oscillator circuit into the I.F. A trimmer was provided to off set this. It did work very well but as customers never complained about the line structure with 405 line pictures, even 21" models, there seemed little point in the added expense as Peter suggests. They could see no difference with the switch on even if pointed out to them...I think the Ekco T164 [15" 1951] was the first to use it and the last was either some versions of the KB VC1 chassis as suggested by Daz or the Nera projection set around a year later.
I think the KB supplied a 'ripple' current to the tubes first anode rather than a seperate oscillator and coils. After such a long time the memory tends to loose its magnetism...
Regards, John.
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Old 23rd Nov 2008, 11:05 am   #7
Alan Stepney
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Default Re: Spot wobble

The one I recall with the switch, would have been an Exco.
I never felt that the effect was worth the effort of pressing the switch, let alone that of designing and adding the circuit required.

I just wondered which other makers tried it and who was the last to discontinue it.
KB,it seems.
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Old 23rd Nov 2008, 12:11 pm   #8
ukcol
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Default Re: Spot wobble

I seem to remember a White Ibbotson set from the distant past that used spot wobble. Anyone any idea what model that may have been?

It would have been long before the KB of course.
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Old 24th Nov 2008, 12:04 pm   #9
ENGLISH VICTOR
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Default Re: Spot wobble

The Ecko 231 was the last model I saw spot wobble on. It operated between 10-13MHz. depending on the channels operating in your area. Everything John said is as I remember it. My opinion was that it was rarely ever used, I did not like it because it seemed to make the picture a little fuzzy. While the CRM171/2 was in good shape the picture quality was fantastic, sharp, bright and well interlaced while at the proper viewing distance the line structure was not visible so why slightly soften the picture.
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