• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Sharing Meter with Switch

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Maybe someone thought it has some form of non linear resistance like a fuse that really does.

Nah, leave it in circuit. You could always try some blind A/B testing with your friends but I really don't think anyone or any measurements will tell a difference. That is as long as the wiring isn't six feet long🙂

Cheers
Matt
 
Just for info, I have a rather nice GE(UK) meter with the UK's government crows foot stamp on the scale that I inherited from my grandfather. It is a 25uA movement! Pretty impressive. It was new in its box. The terminals were shorted with a wire wound round them for postage/shipping but it also has two back to back germanium diodes across the terminals. I would date it around 1955-6. The diodes protect the movement from excessive voltage. Funny thing is that when the movement is returning to zero it generates enough back EMF to turn on one of the diodes. The movement returns to zero really slowly. Possibly has thousands of turns of wire way, way thinner than a blonde one.

Cheers
Matt
 
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Progress. I was already monitoring the current through each GM70 with a PIC and INA122 op amps....the light went on and I tapped the INA122 output for the meters...duh!
Works great and no switching noise.
 

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