Help with Scroggie sensitive null detector build - UK Vintage Radio Repair and Restoration Discussion Forum

mpegjohn · 28th Jul 2019, 5:20 pm

Dear all,
I have embarked on building this piece of test equipment, designe by Scorggie:
https://www.americanradiohistory.com...ld-1951-05.pdf

Wireless World May 1951 Page 175.

I have built it and am getting a good response on the meter. The feedback control works great.

I have two problems. First is in the frequency selectivity. The tuning control seems to do little.
The frequencies published for the ranges, don't seem to match calculated Wein bridge frequencies.

For example Range E is said to be 1.48KHz - 2.08KHz. My calculations show 2.122KHz -3.183KHz. I am using f = 1/(2 xPI x c x r).

Has anyone built one of these units?

How can I test the bridge network on its own?
I tried a generator across it, and then looking at the centre (point 1) on a scope, but it was flat. Looking at the other side of the 100K I do see a peak of sorts.

Many thanks,
John.

28th Jul 2019, 5:20 pm	#1
mpegjohn Hexode Join Date: Aug 2013 Location: Chichester, West Sussex, UK. Posts: 270	Help with Scroggie sensitive null detector build Dear all, I have embarked on building this piece of test equipment, designe by Scorggie: https://www.americanradiohistory.com...ld-1951-05.pdf Wireless World May 1951 Page 175. I have built it and am getting a good response on the meter. The feedback control works great. I have two problems. First is in the frequency selectivity. The tuning control seems to do little. The frequencies published for the ranges, don't seem to match calculated Wein bridge frequencies. For example Range E is said to be 1.48KHz - 2.08KHz. My calculations show 2.122KHz -3.183KHz. I am using f = 1/(2 xPI x c x r). Has anyone built one of these units? How can I test the bridge network on its own? I tried a generator across it, and then looking at the centre (point 1) on a scope, but it was flat. Looking at the other side of the 100K I do see a peak of sorts. Many thanks, John.