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Bell & Howell Oscilloscope Model 34 DeVry Tech

The Bell & Howell Oscilloscope Model 34 was purchased at an auction and then give to me. It was made by Heathkit for DeVry Tech (DeVry University). Below is a photo of the front after I finished electronically going through it.


There was nothing interesting that came up while working on it. Below you can see some before and after of the underside.




Below is the top side. The 2 filter cans were 4 sections of 20mfd for a total of eight 20mfd capacitors. 

Below is the solution I came up with to replace them. It consists of eight 22 mfd on a PCB that is zipped tied to the bottom of the chassis.  




Overall this is a simple oscilloscope and was a simple electronic restore. 

Here is the schematic.

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  1. Joe PugliseFebruary 18, 2020 at 12:51 AM

    Hi Cody, I was given the exact scope from a relative and since I have only basic electronic repair experience, I was wondering if you could possibly point me in the correct direction towards doing some basic diagnosis on the unit? Removed cover and did a visual inspection. Unit is VERY, very clean inside and out. No bulging or burned components or caps. All components look like brand new (I know you can't tell from cosmetics, just saying). All tubes heat-up and glow including the back of the scope tube, however no trace is visible at any intensity. Guess I should start with the caps. Is there anything you would recommend first. Thanks in advance for any suggestions.

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    1. CodyFebruary 21, 2020 at 9:35 AM

      Mine surprisingly worked when I initially powered it up before I began any work. Not a lot of advice I can give to you. If you are familiar with electronics and high voltages you may want to check for B+ coming off the 6X4. My other thoughts would be to check for any voltages missing on the plates.

      Good Luck,
      Cody P.

      Delete
  2. UnknownFebruary 6, 2022 at 9:59 PM

    hey cody! i've got the same model and i'm trying to understand the pinout of the filter cans. I've got a bunch of 450v 22mfd caps for replacement. These shouldn't be in series right? There's only 4 pins on the filter cans so I assume each one holds a capacitance between its corresponding lead and ground, with the cans bolted connection serving as the ground?

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