UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

waran2005 · 2nd Mar 2023, 1:42 pm

Thanks Tony, great advice about the rust removal process for the handle machine screw, I will look into getting that done. I also didn't realise that they are pinned in place, I tried to remove one and gave up thinking it must be seized, so decided not to pursue any further.

Well, I have made some more progress to my VCM, I fitted the new op amp board, replaced most of the electrolytic capacitors, although I have one left to do on the power board.

Refurbished knobs fitted, valve panel refitted. It all works really nicely, but I've not progressed with the calibration as there is still a discrepancy of 1.5 mA on the 30 mA range, 100 and 10 mA read equally, so something is not quite right, further investigation required, although I have checked those resistors once already.

So it is working, oh, and the B9A valve socket needs replacing, not a major issue as I can use the adaptor I refurbished the other day that came with it, a sort of mini side project.

Anyone have any idea regarding the discrepancy for the 30 mA range, apart from the shunt resistor?

2nd Mar 2023, 1:42 pm	#43
waran2005 Tetrode Join Date: Feb 2020 Location: Cardiff, Wales, UK. Posts: 65	Re: AVO VCM 163 Meters Thanks Tony, great advice about the rust removal process for the handle machine screw, I will look into getting that done. I also didn't realise that they are pinned in place, I tried to remove one and gave up thinking it must be seized, so decided not to pursue any further. Well, I have made some more progress to my VCM, I fitted the new op amp board, replaced most of the electrolytic capacitors, although I have one left to do on the power board. Refurbished knobs fitted, valve panel refitted. It all works really nicely, but I've not progressed with the calibration as there is still a discrepancy of 1.5 mA on the 30 mA range, 100 and 10 mA read equally, so something is not quite right, further investigation required, although I have checked those resistors once already. So it is working, oh, and the B9A valve socket needs replacing, not a major issue as I can use the adaptor I refurbished the other day that came with it, a sort of mini side project. Anyone have any idea regarding the discrepancy for the 30 mA range, apart from the shunt resistor? Attached Thumbnails