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Zero Cool 18th June 2011 08:39 PM

Precision Atten for Tek SG505
I find the variable output control on my SG505 to be to course and hard to adjust precisely. part of it is due to Tek's use of a fiberglass rod for the control shaft. there is a degree of torsional flex combined with the stiction of the control make it hard to adjust in small increments.

I want to build an external precision attenuator using a 10 turn pot. coarse adjustment would be made with the 505's control and then slight additional attenuation using the external control to zero in on the exact level.

What value should the pot be?

dinos8746 19th June 2011 09:31 AM

It is not so easy. Theoretically, you must replace the variable R1518 (TEK part number 315 1403 00), with a multi turn pot, of the same size and the same value of 5Kohm. But be careful, because it is behind the (fragile) step attenuator. You must find a way to place it, in the right position and connect it with the flexible shaft and also to preserve the on - off switch on the back of the R1518. All the work refers to A12 board (main board).

Zero Cool 19th June 2011 02:39 PM

Oh no i didn't mean i wanted to replace the INTERNAL control i want to build and external attenuator box that would connect between the output of the SG505 and the device under test.

dinos8746 19th June 2011 04:34 PM

This way you alter the impedance of the SG505, which is crucial for proper measurements. Even with DUT with high input impedance there will be a mistake in the absolute level. I wouldn’t recommend such a modification.

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