Update: 2nd life for a 575 / capacitor condition facts


Joe
 

Hello,
as I had initially planned my objective was to exchange all and every "suspicious" capacitor and these selenium rectifiers. Right now I have got a basically well operational instrument, but not yet calibrated as I am still looking for other suspects.

My findings (results read from a Chinese component checker):
1. Bumble Bees: all 10 - 35% off nominal value, VLoss 1.0 - 2.8%
2. High Voltage capacitors (1kV, 3kV, ...): VLoss 1.5 - 2.0%
3. Good-All capacitors: 5 - 12% off nominal value, VLoss < 1%
4. Black Sprague capacitors: 15 - 30% off nominal value, VLoss 1.2 - 2.4%
I have tested that Chinese instrument against a Siemens metal casing precision capacitor of 90.000 pF 0.5% first and it gladly agreed to the printed on values ;-)

So I believe it was very well necessary to retire ## 1,. 2. and 4. whereas these Good-All seem to be still strong.

Next I will have a look how well the seleniums perform. Let's see!

Regards, Joe


Brenda
 

Hello Joe,

I use a capacitor checker from Mr. Carlson's Lab, and that works very well. As far as your list of capacitors goes, I have had very good luck with Good-All capacitors! I have checked many of them and they were doing very well with no leakage. However, I have yet to find 1 Bumble Bee that is not leaky. I still test those but most likely they are replaced. High voltage capacitors, well, my checker can test them for leakage, but if the are the disc type, those should be fine. I have found the the Black Sprague capacitors goes, there are 2 different colors. And in my experience, the black caps with the yellow writing tend to be very leaky while the ones with the red writing don't have the leakage issues. I have one of those Chinese testers myself, does a rather pretty good job for a go-no go test!

Seleniums on the other hand tend to scare me. It's only a matter of time before those will fail, and I had one blow out that nasty smoke and believe me, was not pleasant to deal with. My whole house reeked for a long time before it cleared out. I actually have a conversion kit pulled from an old 531 scope sitting around somewhere, but I don't know if that would work with a 575. That is one piece of Tektronix equipment that I would love to have.....for a reasonable price that is.

Brenda


Joe
 

Hello,

right now I assume I have examined almost all possible suspects (capacitors) in the 575. In addition to my above discussed list above here are test results for black body "Sprague 160 P" capacitors stamped with red letters, rated 0.047 µF rated 400 V DC. There are three individuals that have been checked:

No. 1 measured 0.062 µF, V Loss 1.8 %
No. 2 measured 0.067 µF, V Loss 2.2 %
No. 3 measured 0.062 µF, V Loss 2.1 %

No question, these capacitors now have been retired! It is time to reassemble the instrument and post some photos soon.
Well, then I will need the to build the VTCT adaptor. And there are even some more "boat anchors" sitting on my bench, waiting to be taken care for: A 585 and a 565.

Regards, Joe