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 Post subject: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 4:41 am 
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Joined: Apr Thu 10, 2014 3:29 am
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Location: Oak Harbor, WA 98277
I’m working on a 1920’s Readrite Model 400 tube tester currently. I’m having a moment and am not quite interpreting part of the schematic adequately. Anyone care to throw me a bone?
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What exactly is going on here?

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21 years of reading 2 inch thick booklets of aircraft schematics and this guy has me stumped.


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 4:47 am 
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Plate Cap, perhaps? It's tied to the "Red" bus, which connects to all of the plate connections on the sockets.

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PC.jpg
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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 5:02 am 
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Joined: Apr Thu 10, 2014 3:29 am
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Location: Oak Harbor, WA 98277
That would make sense, but I believe this to be the cap lead in this application.

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I should note, that when I opened it up, there was only the one lead going to the Plate bus.


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 5:14 am 
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Andrew Cummings wrote:
That would make sense, but I believe this to be the cap lead in this application.

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That connects to the blue bus/grids. It's the grid cap lead. Follow it to the extreme right, then up to the "blue bus"...

EDIT: Looking closer, the connection to the 12K resistor could be a binding post for bringing in the HV ot the plates...

EDIT II : Or a ground, with the power coming in on the lead marked "primary"

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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 5:26 am 
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Ad shows only one clip lead.....

http://www.americanradiohistory.com/hd2 ... e%20400%22

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USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 5:49 am 
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Not germane at the moment, but some adapter schematics for the 400:

http://www.americanradiohistory.com/hd2 ... e%20400%22

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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 5:59 am 
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Joined: Apr Thu 10, 2014 3:29 am
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Location: Oak Harbor, WA 98277
Thanks for the links, I did not have that info.

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Thats the part I’m struggling with, there was no 12k resistor. Only the 5k wire-wound in the battery compartment going to the + terminal of the ammeter.

Obviously does not mean that it was correct in being that way.


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Fri 21, 2019 6:12 am 
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Joined: Jan Tue 10, 2012 8:39 am
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It seems to be a picture of a solder lug or similar. Something that goes over a post or screw and gets clamped or screwed down. I doubt that it's a plate cap. But it's something on the end of a wire.

I think it's to test the battery. The 12k resistor goes to the battery and the meter indicates its condition.


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Sat 22, 2019 4:36 am 
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Joined: Apr Thu 10, 2014 3:29 am
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Location: Oak Harbor, WA 98277
Possibly, I remain unsure about that part of the schematic and there was nothing inside the unit to reference.

What I am sure of is that for such an old tester, it reads comparable to my I-177. The ammeter is a tad finicky though, you have to hold it at angle to get a reading.


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Sat 22, 2019 8:30 am 
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Greetings to the Forum:

I believe that symbol means "Connect to Pac-Man Video Game". :D

Regards,

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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Sat 22, 2019 11:58 am 
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Pretty restoration. I think I've got one of those in the collection waiting for me.

As to your meter being erratic, you might be able to fix it. Possible that there is "crud" in the movement... you might be able to clean it out with just a sliver of paper. I'd avoid using compressed air.

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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Sat 22, 2019 4:09 pm 
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Here's a drawing for an ad that shows a second lead with a contact of some kind. I lean towards it being a plate connection but the 12k resistor would certainly affect the readings. So maybe a grid contact.

https://www.radiomuseum.org/r/readrite_tube_tester_400.html


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 Post subject: Re: Tube tester schematic help
PostPosted: Jun Sat 22, 2019 5:42 pm 
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Joined: Apr Thu 10, 2014 3:29 am
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Location: Oak Harbor, WA 98277
khutch wrote:
Here's a drawing for an ad that shows a second lead with a contact of some kind. I lean towards it being a plate connection but the 12k resistor would certainly affect the readings. So maybe a grid contact.

https://www.radiomuseum.org/r/readrite_tube_tester_400.html

Well I’ll be.

I saw that image but didn’t catch the lead sneaking out if the power cord grommet. Easy enough to build, but I’m not going to mess with it unless I find an actual need for it I think. I have no real tube data for it and already have calibrated testers so I think this will end up in the display case. Interestingly, there was no cut lead or evidence on the terminal of that lead ever being present. Fun project though.

Barry H Bennett wrote:
Pretty restoration. I think I've got one of those in the collection waiting for me.

As to your meter being erratic, you might be able to fix it. Possible that there is "crud" in the movement... you might be able to clean it out with just a sliver of paper. I'd avoid using compressed air.

This ammeter is in a crimped shell, it would be major surgery to open it up I think. Probably not worth the risk to the meter. If I find a substitute ammeter of the correct size and range, I’d consider swapping that in and keeping the Readrite labeled original tucked away for historical purposes.

If it’s going to see more than occasional use, I will need to reconstruct the piece of fiberboard the “push” button is on. It has long ago lost its firmness and not longer springs the button back up properly.


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