Defective Avo vcm 163 gm meter substitution - UK Vintage Radio Repair and Restoration Discussion Forum

LA9CHA Thorvald · 9th Apr 2024, 7:32 pm

Hello again, I have a avo vcm 163 that needs a replacement gm meter. My plan is to use an op-amp amplifier pcb, using the original input signal from the vcm to the meter and use a 100uA meter. I think the op-amp input circuit must be similar to the gm meter load resistance (I beleave about 1,5Kohm but is not sure as the meter coil is broken an can not be neasured. Are there any precaution regarding the output from the op-amp driving a replacement meter? I have a circuit (maybe made by Martin, Decatron), and I have earlier made a replacement for the ma/v meter on a avo mk3. So far this has worket out fine. Hints and advices are most welcome!

9th Apr 2024, 7:32 pm	#1
LA9CHA Thorvald Pentode Join Date: Dec 2019 Location: Egersund, Norway Posts: 208	Defective Avo vcm 163 gm meter substitution Hello again, I have a avo vcm 163 that needs a replacement gm meter. My plan is to use an op-amp amplifier pcb, using the original input signal from the vcm to the meter and use a 100uA meter. I think the op-amp input circuit must be similar to the gm meter load resistance (I beleave about 1,5Kohm but is not sure as the meter coil is broken an can not be neasured. Are there any precaution regarding the output from the op-amp driving a replacement meter? I have a circuit (maybe made by Martin, Decatron), and I have earlier made a replacement for the ma/v meter on a avo mk3. So far this has worket out fine. Hints and advices are most welcome!