Skip to main content

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.


  1. 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.

    1. 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.

  2. 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?


Post a Comment

Popular posts from this blog

6J1 Preamplifier

6J1 Preamplifier I purchased this 6J1 amplifier from eBay. The seller was located in China. Below is a my experinces building the preamp. I have not had a chance to give it a full test. I will update this post once I have had that chance.  It took a little over an hour and a half to finish building the kit. The board seemed a little tight for installing everything. The board itself runs on 12AC and from what I can gather it takes the 12AC and runs it through a voltage doubler which then gives the "B+" voltage.The tubes are 6J1's and obviously have 6volt filaments that run in series. I can not find a lot of info on the 6J1. Link to Data Sheet . There is not a lot of instructions. Most everything is in chines and so I cannot read it. I was able to follow down the parts list and figure out what everything was and where everything went. I used a multimeter to check the resistors before installing them because the colors were not easy to interrupt. Overall this is

Philco P933-124 from 1966

I have been wanting an AM/FM tube radio. I found this one eBay fairly cheap and I love Philco products.  The eBay listing said the radio worked as is. Below is how I received the radio. I was very pleased with the packing! The radio was all original from what I could tell and had a great sound. I went ahead and disassembled the radio and replaced the electrolytic capacitors. The radio has a great sound and very sensitive.  Below is the schematic.

Seeburg Digital Control Center

The Seeburg Digital Control Center came into use around the 1970's. This was model DDC1. Seeburg continued the use to the digital control center line until around 1977. The last model used was a DCC42-56. The DCC is used to supply 27 volts DC, -27 volts  DC and -13 volts DC to the jukebox. The DCC has test points on the side to measure these voltages.  Below you can see a DCC3. Once you flip over the DCC you will see two circuit boards. The top board is the data buffer board. Generally you will not have any issue with it. The second board (on bottom) is the power supply board. This where you may have issues. The power supply board is where the DC voltages are created and regulated. Below is the power supply board removed. The first thing I always do when working on a DCC is start by replacing all electrolytic capacitors. Below is the schematic.  In my case as you can see below I had other issues. As you can see transistor Q3120 has been repla