In search of holdoff pot for 2235


Ozan
 

Link didn't come out right in previous post:
Schematic (sheet 4) in https://w140.com/tekwiki/images/3/30/070-4206-00_2235_Service_Manual.pdf shows 50k-ohm for R5921
Page 182, location A-3

Ozan


 

I've found other typos in the Tek service manuals, especially in the parts lists. I have seen several examples of dropped or doubled letters in part numbers (I think it was in a 475 service manual where someone had typed either FD70003 or SAB41113 instead of FD7003 or SAB4113, but I am unable to find the error at this moment), so I would be surprised to find that they dropped the K somewhere.

-- Jeff Dutky


Ozan
 

Schematic (sheet 4) in w140.com shows 50k-ohm for R9521 although part list shows as 50-ohm. From the schematic 50k looks right, 50-ohm change wouldn't make any noticeable change in timing (Thevenin equivalent resistance of R519/R520 junction is is 3.89k).
Ozan


rick
 

can you post a link to a picture of the pot? Is it an RV6 mil-style pot, a mod-pot (which allen bradley sold to Clarostat) or something different. Perhaps someone has something that fits?

--rick chinn

At 05:45 PM 1/15/2021, you wrote:
Due to a freak accident, the shaft of the Variable Holdoff potentiometer broke and I need to replace it. The details are:
R9521 311-2146-00 Res, Var, Nonwir: 50 ohm, 20% 0.5W CM41773
It is a Clairstat p/n.
After doing a number of google searches, I am coming up empty.
Can someone please point me a source of the part?
(I am afraid that because it is so old, it may be NLA anywhere)
Thank you
Best regards
J


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adesilva_1999@...
 

Last night I was trying to locate it on the schematic but fell asleep after a little time! Can you email me a picture of the broken part? If you are in the US, I might be able to help you repair it.


John Hudak
 

I will check with my DMM. I haven't disassembled the scope yet as I wanted to have the part in hand so I could swap out the part and reassemble it and not have it sit on the bench for a week or more till the part arrives.

When I looked in the SM and saw it rated at 50 ohms, it struck me as very odd. 50K seems more reasonable but higher than I would have expected. I need to find it on the schematic. Hopefully that will confirms the value, Looking at how it is used in the circuit should provide the definitive answer.
thanks for the suggestions


adesilva_1999@...
 

It should be 50k. Best is to check the two end tags with a meter. You may have to un-solder the wires.


John Hudak
 

clarification: it is a Clarostat.
Confusion: the Tek SM says it is a 50 Ohm pot which seemed wrong.
Searching I turned up says it is a 50K pot.
https://www.sphere.bc.ca/test/tek-parts/tekpots.html
Can someone clarify?


adesilva_1999@...
 

Try this site: http://www.smcelectronics.com/tekpart.htm

If you cannot find it there, post a photo of the broken parts and we can see if we can give some ideas depending on how it is broken.


 

part number came right up on eBay: https://www.ebay.com/itm/Tektronix-2235-oscilloscope-Variable-hold-off-potentiometer-311-2146-00-50Kohm/124429504441

Of course you could also pickup an entire parts mule for not much more.


John Hudak
 

Due to a freak accident, the shaft of the Variable Holdoff potentiometer broke and I need to replace it. The details are:
R9521 311-2146-00 Res, Var, Nonwir: 50 ohm, 20% 0.5W CM41773
It is a Clairstat p/n.
After doing a number of google searches, I am coming up empty.
Can someone please point me a source of the part?
(I am afraid that because it is so old, it may be NLA anywhere)
Thank you
Best regards
J