Levell TG66 Meter Not Zeroing - UK Vintage Radio Repair and Restoration Discussion Forum

DMcMahon · 1st Oct 2022, 4:13 pm

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

frsimen · 1st Oct 2022, 5:43 pm

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

Radio Wrangler · 1st Oct 2022, 7:19 pm

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

DMcMahon · 1st Oct 2022, 7:26 pm

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

Tim · 1st Oct 2022, 7:27 pm

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.

DMcMahon · 1st Oct 2022, 8:25 pm

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

1st Oct 2022, 4:13 pm	#1
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	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 Attached Thumbnails

1st Oct 2022, 5:43 pm	#2
frsimen Heptode Join Date: Jan 2011 Location: Croydon, London, UK. Posts: 773	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

1st Oct 2022, 7:19 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,874	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 __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

1st Oct 2022, 7:26 pm	#4
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	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 Attached Thumbnails

1st Oct 2022, 7:27 pm	#5
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	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. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

1st Oct 2022, 8:25 pm	#6
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,603	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