?Exactly. High-gain plugins (Type B, D, etc) were seeing hum on the calibrator. The resistor made the bottom ranges usable.
In the 535 Mod Summary, it's Mod #1412, effective S/N 5001.
Dave Wise
My "S/N 75" 535-535A prototype needs this mod.
________________________________
From:
[email protected] <
[email protected]> on behalf of keantoken via groups.io <keantoken@...>
Sent: Thursday, March 25, 2021 9:28 AM
To:
[email protected];
[email protected]Subject: Re: [TekScopes] 0.25R resistor in calibrator ground
I noticed the same resistor, also open, on my 561B! On Thursday, March 25, 2021, 11:18:00 AM CDT, cmjones01 <chris@...> wrote:
I've just noticed something odd about the calibrator outputs on my
535A scope and 127 plugin power supply. They both have a 0.25R
resistor in series with the calibrator socket's ground connection. The
reason I noticed is that the 127's resistor is open-circuit, so
connecting the calibrator to another piece of equipment left the
ground disconnected, with the expected symptoms.
I couldn't find any information in the manuals as to why this resistor
is there. Why is it? To avoid ground loops?
Chris
