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Old 7th Jun 2021, 10:54 am   #1
BrianAllen
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Default Philips 790A/Mullard MAS4 TI Tuning Indicator?

Please correct me if I am wrong but I believe that the attached pics are of a tuning indicator from the above sets.

Can anyone please confirm that it is and how it operates.

Thank you.

Brian
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Old 7th Jun 2021, 11:15 am   #2
ms660
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Default Re: Philips 790A/Mullard MAS4 TI Tuning Indicator?

Yes, it's the tuning indicator, a moving iron ammeter that indicates the anode current for the IF amplifier valve which will vary according to the signal strength due to the AGC action on the valve which is of the variable mu type.

Lawrence.
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Old 7th Jun 2021, 11:19 am   #3
BrianAllen
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Default Re: Philips 790A/Mullard MAS4 TI Tuning Indicator?

Brilliant, thanks Lawrence.

I could here movement inside the casing, so your post explains all.

Thank you.

Brian
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Old 7th Jun 2021, 11:25 am   #4
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Default Re: Philips 790A/Mullard MAS4 TI Tuning Indicator?

It may be a shadowband or a spot of light that moves on the screen, so there may be a bulb in there.
But as Lawrence says it is probably a moving iron type of movement. The one I had in a GEC BC3550 had an open circuit coil. This needed to be rewound as it supplied the current to the IF valve. https://www.youtube.com/watch?v=WSuzL3Yeni8
Mike
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Old 7th Jun 2021, 11:35 am   #5
BrianAllen
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Default Re: Philips 790A/Mullard MAS4 TI Tuning Indicator?

Noted, thanks Mike.

Brian
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