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Messages - henry909

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Amplifier Discussion / Re: Grounding techniques
« on: October 12, 2012, 01:21:09 AM »
I came to this forum looking for info to help solve a grounding problem with an old amp. And here the first thread I find is about grounding. But I am not sure whether I understand enough of the discussion above to figure out how to solve my problem.

Problem: I have an old Kay Model 780 SS amp. It has an old style two prong power cable, i.e., it doesn't have the third ground prong. The amp produces a lot of static and when you touch metal on the guitar , eg., the whammy bar or the bridge, you can hear static clicking through the amp. I suspect that the problem is the lack of ground on the power cable which goes through a grommetted hole in the chassis.

Can anyone give me an explanation of of how to add a ground to the power cable to see if that eliminates or reduces the static? Can I remove the chassis disconnect the old power cable. Then connect the two non-ground wires where the original power cable was connected and then simply screw the ground wire to the chassis?  Thanks.

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Thanks for the replies.

Enzo:

I tried the tests you suggested.  When I put the meter on a100k resistor I get 99.9 (200k ohm setting); when I tried it on the pot again I get 103.3.

Re: The taper. This test is more problematic because the problem with this pot is that the shaft pulls out of the body and I am not sure I am getting the half way point. But at the half way point as nearly as I can find it I am getting 68.4 on one side and 35.9 on the other.

what do you think the value of the pot is based on this info?   Thanks again for your help.

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I have an old RMI 140 solid state amp with a broken pot (the shaft pulls out of the body).  I am trying to find a replacement  but the pot does not have typical marks such as  "A100K".  I tested the pot with a multimeter (dial set to  200k ohms) and got a reading of 101.1.  The only markings on the pot are  "CTS", "USA",  "204-1040",  and "1376927".  Can anyone help identify the value of this pot?  Thanks in advance for any help with this problem.

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