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 Post subject: BK 675 Tube Tester alterations
PostPosted: Oct Wed 07, 2020 10:48 pm 
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Location: Mesa, AZ 85206
Hi Folks

I am starting to spiff up the BK 675 I got a few months ago.

I have tons of original documentation, but no schematic/parts list.

The only schematic I could find was at BAMA, but it could be of better.

anyone out there have a good copy and parts list?

Thanks!

Steve

Edited: see following post


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 Post subject: Re: BK 675 Tube Tester alterations
PostPosted: Oct Fri 09, 2020 9:50 pm 
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Location: Mesa, AZ 85206
Now that I am taking a really good look at this piece, it becomes clear that there have been alterations.

I had started replacing the electrolytics, and initially thought I could figure out what went on the now "empty" lugs of the terminal strip that still have evidence of old wiring (yellow arrows)...but, nothing was easily visualized.

The clipped wires on the transformer may have been factory (also arrowed).

It is possible that this unit was modified to bring the grid emissions control potentiometer out the front panel which mine has (which others have described)...I have documentation that describes that being done on later models...but the schematic I have is earlier and doesn't jive in many ways...particularly in the grid emissions control circuit.

So, it is possible that this unit was updated, control moved, and wires re-routed....there is some discoloration (another arrow) that suggests that might be the case.

If anyone has one of these guys, I would appreciate some help in the way of pics or descriptions that might let me figure this out,

As it stands, I will have to delay further work on it until I have more clarity.

Thanks!
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Steve


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 Post subject: Re: BK 675 Tube Tester alterations
PostPosted: Oct Sat 10, 2020 5:23 pm 
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Location: Mesa, AZ 85206
OK..Here's the answer.

After a few hours of digging, I re-read the calibration instructions for the BK 650, and realized that the ASM-7 kit had been installed with the recommended alterations. This kit fine tunes the gas sensitivity.

To help others, I have revised the attached 675 schematic to reflect those changes. The attached should pertain to any 675 with this modification.

Hope this helps someone in the future...perhaps this will be a search return for the next person.

sorry about the edits...trying to get the attachment right...

Steve


Attachments:
BK 675 Schematic with ASM-7.png
BK 675 Schematic with ASM-7.png [ 428.57 KiB | Viewed 292 times ]
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 Post subject: Re: BK 675 Tube Tester alterations
PostPosted: Oct Tue 20, 2020 12:53 am 
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Joined: Mar Sun 20, 2016 11:04 pm
Posts: 784
Location: Mesa, AZ 85206
Well, with the help of Mike Higgins, I have cobbled together a working schematic and am documenting the changes that have taken place over time with this tester. I am also documenting on the schematic voltages and test points.

I talked to B&K today...no dice; they have no access to a clean, complete schematic...So, I "bumped" here hoping someone might emerge with a lead.

In searching, I found posts from radious about his/her experiences, and I have PMed them, but to date no response and no recent posts....hope they are OK with all the COVID stuff.

When I am done, and the piece is working, I will ship it off to BAMA as well...I have much original documentation.

BTW, on the pics you can see green goop on one of the terminals...three of the lamp sockets were covered in it, and removing the bulbs was a chore because the green goop stuck the contact in place so I could not push the bulb in...wonder if that goo was factory or after...

Steve


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 Post subject: Re: BK 675 Tube Tester alterations
PostPosted: Oct Sat 24, 2020 8:53 pm 
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Joined: Mar Sun 20, 2016 11:04 pm
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Location: Mesa, AZ 85206
Even though another post is working on the Gm issue, I wanted to post here my "final" schematic that details what I have learned, and the details of replacing the selenium rectifiers with silicon rectifiers and achieving the correct 140V output. If one looks at the other post, I changed them to to be certain that the old seleniums were not affecting the screen voltages in invisible ways that were affecting Gm readings.

This is just for information for the next poor soul who wants to take one of these on....

It is just an odd duck...the card system is a nightmare....

Steve


Attachments:
675 schematic position 1 for a 6L6 .jpg
675 schematic position 1 for a 6L6 .jpg [ 517.28 KiB | Viewed 139 times ]
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