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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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16th Nov 2022, 12:25 pm | #1 |
Tetrode
Join Date: Feb 2020
Location: Cardiff, Wales, UK.
Posts: 65
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Mk3 VCM additional resistor
Hi all,
During my repair of my Mk3 VCM I have come accross a resistor that I'm unable to identify on the circuit diagram. It is a resistor fitted accross R28 and R29 of the meter switch and so will be in circuit for the 25, 10, 2.5 mA and (test) mA/V positions, not the 100 mA positiin? As far as I am aware it should not be there, it reads around 1k, colours are old / faded so difficult to exactly identify the original value. Is anyone aware if this is an AVO modification, it appears to have been there for some time and appears to be an identical type as used on R1, the 3.9 Ohm resistor, so looks original. Any help appreciated, now would be the time to remove it if it's not meant to be there. Thanks all. Waran. |
17th Nov 2022, 9:17 am | #2 |
Octode
Join Date: May 2009
Location: Linkoping, Sweden
Posts: 1,463
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Re: Mk3 VCM additional resistor
There are a few errors in most AVO VCM schematic diagrams and in the Mk III there is an error with the Inner-Outer Slope switch, a resistor is missing in the circuit there, if you compare with the Mk IV you can see that resistor. That resistor is 750 Ohm in some testers and 1000 Ohm in some.
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Martin, Sweden |
19th Nov 2022, 12:27 pm | #3 |
Tetrode
Join Date: Feb 2020
Location: Cardiff, Wales, UK.
Posts: 65
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Re: Mk3 VCM additional resistor
Hi Martin,
Brilliant, thank you, that makes a lot of sense. It didn't occur to me to check the schematic of the MK4. Kind regards, Waran. |