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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Tue 06, 2018 8:39 pm 
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Joined: Feb Mon 13, 2017 5:42 pm
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Location: Gualala, CA, 95445
Thanks. Antique Radio Supply has some multiple 20 mF can caps, but they are $38 or so each! Not sure if they are the right physical size.

Looks like the CRT is slightly curved.

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 12:29 am 
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Joined: Feb Mon 13, 2017 5:42 pm
Posts: 111
Location: Gualala, CA, 95445
See:

https://www.tubesandmore.com/products/c ... ectrolytic

and

https://www.tubesandmore.com/products/c ... v-202020-f

I wonder if the measurements are acceptable (a good fit)?

Pricey, but if it is basically drop in and re-connect, it might be worth it.

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 1:08 pm 
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Not sure if they will fit. Best thing to do is look at the dimensions of the new cans then measure the original cans and see if they are nearly identical. If so then check to be sure the new cans have the same tabs as the originals.

If so use them.

If not you will have to do like I did.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 4:30 pm 
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Location: Gualala, CA, 95445
I kind of like the idea of rebuilding them. It might also save quite a bit of money!

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 4:39 pm 
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Location: Gualala, CA, 95445
How did you cut the capacitor cans open?

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 8:33 pm 
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Think I used a Dremel with a small cutoff wheel installed.

I'll get a picture or two tomorrow showing where the cans need to be cut.

Now if the cans were visible from the outside I would have bought new cans, but since they are on the inside I thought why.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 07, 2018 8:50 pm 
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Location: Gualala, CA, 95445
Thanks.

Richard


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 Post subject: Re: OS-8 oscilloscope repairs
PostPosted: Feb Sun 11, 2018 8:15 pm 
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Joined: Feb Mon 13, 2017 5:42 pm
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Location: Gualala, CA, 95445
I got the side of the OS-8 off and can see the power supply.

It looks like it is secured by four small machine screes. If those screws are removed, is the power supply free to come out of the box? Which side?

It would see to be quite difficult to get the washers and nuts back on the screws when re-assembling!

Are there other capacitors that it is best to replace in addition to the two "can" type capacitors in the power supply?

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Sun 11, 2018 8:52 pm 
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Yes all other paper capacitors and if there's other small electrolytic caps replace them too.

That's for the whole scope.
Forget which side I took the supply out of. Whichever side the wires going to the supply allow it to come out.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Sun 11, 2018 9:11 pm 
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Location: Gualala, CA, 95445
Thanks. I like your hat.

Tricky to put the screws back in?

Richrd


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Mon 12, 2018 4:15 am 
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You're welcome and thanks.

I forget if it was tricky for the screws.

Also replace all non-wirewound resistors with 1% metal film resistors wherever possible. Given the chassis of the scope are so compact you don't want to have to go back in later to replace a failed original resistor.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Feb Wed 28, 2018 10:37 pm 
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Location: Gualala, CA, 95445
I may have time to work on the OS-8 soon. Do you recall where you got the replacement capacitors that you put inside the existing capacitor "cans"?

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Thu 01, 2018 1:30 am 
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I got all the parts from Mouser

https://www.mouser.com/

For the electrolytic capacitors use ones with the highest temperature rating.

For non-wirewound resistors use 1% metal film resistors wherever possible.

Also resistors should be as close to the listed value as possible even if it means putting a resistor or two in series or parallel with another resistor.

Paper capacitors use film capacitors for replacement.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Thu 01, 2018 1:41 am 
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Location: Gualala, CA, 95445
Thanks. What voltage film capacitors?

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Thu 01, 2018 3:55 pm 
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rchrdm wrote:
Thanks. What voltage film capacitors?

Richard


You're welcome.

At least 400 volt DC rated.

My suggestion is look for the 630 volt ones since that is a common voltage rating.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Thu 01, 2018 4:24 pm 
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Joined: Feb Mon 13, 2017 5:42 pm
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Location: Gualala, CA, 95445
Thanks.

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Thu 01, 2018 5:54 pm 
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you're welcome


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 Post subject: Re: OS-8 oscilloscope update
PostPosted: Mar Fri 23, 2018 7:55 pm 
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Joined: Feb Mon 13, 2017 5:42 pm
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Location: Gualala, CA, 95445
Progress Report on OS-8

I ended up buying two new "can" capacitors from Antique Radio Supply. I carefully recorded how the components were mounted to the original capacitors, and then cut out the old resistors. They were solidly wire wrapped and soldered on the old capacitor terminals. I bought new, replacement resistors and the new can capacitors just dropped right into the original mounts. The scope now powers up just fine without blowing fuses.

I mounted a fan on the side to keep it cool and replaced the hot incandescent pilot lamp with an LED. I tried to put a fan inside the case, but this did not work that well. I used a small 12 VDC power supply board inside to power the fan.

I think some more work is needed, though.

I removed the jumpers on the back of the scope (except for the top one) and this helped the trace appear properly. Prior to that, it was down at the bottom of the screen and I did not have control over the vertical position.

What jumpers, if any, should be connected on the back of the OS-8 for normal use?

I am having trouble getting a signal to show even with a 2 Volt, 1 MHz input from my signal generator.

I found this web site that describes this scope: http://blogs.telosalliance.com/found-in ... cilloscope

He said the tubes get "gassy." I tested the tubes and they all looked OK. Should I replace them anyway?

I have checked all the tube voltages and some are off. I will be troubleshooting the scope with a knowledgeable friend tomorrow.

Richard

Richard


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Sat 24, 2018 3:19 am 
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ALL non-wirewound resistors must be replaced.

ALL paper caps and ALL electolytic caps not in the cans must be replaced.

I can take a photo of the back of my scope tomorrow showing the connections.


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 Post subject: Re: OS-8 oscilloscope problem
PostPosted: Mar Sat 24, 2018 3:22 am 
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Joined: Feb Mon 13, 2017 5:42 pm
Posts: 111
Location: Gualala, CA, 95445
OK, thanks.

Richard


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