Re: 577D1 itching issue - Haven't touched since, currently in storage


 

Hi DW,
I get very nervous whenever I start wondering if I can connect a ground to something that I know is directly connected to the AC line. And I am in one of those 115V countries where I was able to get used to being shocked. I'm so scared every time I have to work on 220V wiring that I will do anything to avoid it. I don't know what your mains voltage is but you are risking a very valuable instrument in search of the answer to something that is only a problem to you.

For instance I have used at least five 577s and the flicker and non-zero offset has never bothered me. I did notice it from time to time on various 577s but since it never affected the operation of the 577 it was simply not important. None of this behavior is unusual for a 577. Because you have mentioned this before, and because I have used so many 577s I thought I could convince you from my personal experience that this is not a problem.

With all the 577s I have owned or used I have seen the flicker many times. Because you mentioned it I finally took a close look at it on the 577 I currently have on my bench. I have been using this particular 577D1 (Storage) for two or three years by now so I know it well. The flicker is there on my current 577 as it has been on all the 577s I think I have used. This is no surprise to me. But this time I measured it so you can compare your results to mine.

I thought setting the horizontal deflection to 0.05V/Div. would give me the best chance to see any flicker or non-zero voltages. I then turned the collector voltage to the 1600V range. With the Variac turned down to zero the trace goes 9 divisions across the screen and it flickers faintly in many spots along the trace. That would be the equivalent of a zero voltage of 0.45V.
With each collector voltage setting this is what I get:
1600V: A line 9 divisions across the screen that flickers faintly in many places along the trace.
400V: A line 1 division long at the 4th graticule. Where that ends there is a flickering faint line 3/4 division long.
100V: A line 1 division long at the 4th graticule. Where that ends there is a flickering faint line 1/2 division long.
25V: A spot at the 4th division, a flickering faint line beginning at the spot and extending half a division to the right.
6V: A spot at the 4th division, a flickering faint line beginning at the spot and extending half a division to the right.

The fact that on four collector voltage settings the line or spot is at the 4th graticule tells me I need to tweak an offset or balance trim pot somewhere inside the 577 to move that spot over to the origin.

I recommend that you explore the many different things you can measure with this fascinating tool instead of worrying about the flickering line at 0V. It took me years to do that. Each time I learned how to measure another transistor or semiconductor parameter with my 577 I became a better circuit designer. The versatility of this instrument is so great that I am probably only familiar a third of half of the things it can do. I'm looking forward to all the things I can still be taught by the 577.

You are very lucky indeed to own such a valuable instrument. I can't wait to find out what you design with it.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of KB6NAX
Sent: Wednesday, January 01, 2020 11:52 AM
Subject: Re: [TekScopes] 577D1 itching issue - Haven't touched since, currently in storage

Happy New Year, DW,

Could jumping a clip lead from Neutral to the wiper with the brush
insulated from the windings be useful to diagnose why the ollector
will not go to 0V or near it? My theory is if this causes the
collector to go to 0V or near it then perhaps I have enough resistance
occurring from the neutral terminal to the first windings of the
variac causing the collector issue I am experiencing, would you agree?
That's a bit risky if you forgetfully turn the variac CW. Better to measure resistance between the first turn of the winding and the neutral terminal.
Deteriorated connections are accompanied by increase in constriction resistance. Like to know what you find.

Arden




--
Dennis Tillman W7PF
TekScopes Moderator

Join TekScopes@groups.io to automatically receive all group messages.