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Old 1st Oct 2022, 3:13 pm   #1
DMcMahon
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Default Levell TG66 Meter Not Zeroing

I assume the TG66A Oscillator meter needle should be at the left hand side of the meter display but the nearest it gets with the mechanical adjustment screw fully in one direction is as per Photo 2, Photo 3 shows the meter needle position with the adjustment screw fully in the other direction.

So am wondering if this is a fault and if so the likely reason.

The unit arrived with no mains lead and the mains connector on the unit was a large Bulgin which I ripped out and purchased a IEC C9 connector to fit in its place then to use with a kettle type mains lead. But the C9 connector is currently hiding somewhere so not able to power up to see if the meter needle moves when signal is present.

David
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Old 1st Oct 2022, 4:43 pm   #2
frsimen
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Default Re: Levell TG66 Meter Not Zeroing

Hello David,

I think it is fine, the zero position is the 0 on the red dBm scale. The unit shown on the Radiomuseum site as well as the pictures in the Levell advertisements show the pointer in the same position.

Paula
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Old 1st Oct 2022, 6:19 pm   #3
Radio Wrangler
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Default Re: Levell TG66 Meter Not Zeroing

Note that they've helpfully coloured the DB scale on the meter in red, and also the dB offsets on the output switch in red, to show that they are tied together.

0dBm means 1 milliwatt into whatever impedance the instrument is designed to match.

It dates back to telephone systems where 1mW into a standard phone earpiece was considered the standard level. In a 600 Ohm system it's about 775mV RMS

David
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Old 1st Oct 2022, 6:26 pm   #4
DMcMahon
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Default Re: Levell TG66 Meter Not Zeroing

Thank you Paula, after posting I did wonder if I had jumped the gun and come to incorrect assumption.

I then made time to study the manual and it very clearly states to adjust the meter pointer to 0dBm with power removed, which it easily adjusts to. So as you say it should be fine, later need to get it powered up and see if it actually works.

David
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Old 1st Oct 2022, 6:27 pm   #5
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Default Re: Levell TG66 Meter Not Zeroing

I used to have one of those, when I was a lad( well 20 any way)an earlier all silver one, “aquired” from one of the college throw outs. This might have had a +/- 9 volt supply derived from 2 PP9s. I also remember making a mains supply for it, as batteries were expensive even then and ( due to my ADHD) was worried I might forget to switch it off.
I found the frequency was surprisingly accurate when measured with a borrowed frequency counter. I too seem to remember the arrangement with the meter pointer.
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Old 1st Oct 2022, 7:25 pm   #6
DMcMahon
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Default Re: Levell TG66 Meter Not Zeroing

The TG66A version is mains / battery (4 x PP9 for 33V +/-10% operation), the TG66B is battery with option of Levell PU33 power unit for mains operation.

David
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