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 Post subject: Knight VTVM 83 F 120 won't cooperate! Now Calibration help!
PostPosted: Feb Mon 25, 2019 3:54 am 
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Location: Sugarloaf PA.
Does anyone know what model this is? I'd like to see if I can find the schematic and user info on bama.edebris.com/manuals If it's not on there, does anyone have a schematic for this? I'm new to vacuum tube volt meters! So, I turn it on , switch it to resistance, grab the cable (not touching the lead tip) and the meter goes back and forth :?:


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Knight VTVM.jpg
Knight VTVM.jpg [ 86.55 KiB | Viewed 1367 times ]


Last edited by ychris on Apr Fri 10, 2020 6:53 pm, edited 3 times in total.
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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Mon 25, 2019 4:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3526
Location: Seattle WA US
It took Allied a long time to decide they needed to give their kits model numbers...... Anyway, schematics for two early knightkit VTVMs lacking model numbers are available here:

http://www.nostalgickitscentral.com/all ... _test.html

You will have to figure out if either applies to your meter.

<edit>
Your meter appears to lack jacks for plug-in test leads. I haven't seen any Knight VTVM models with permanently wired-in test leads. Could this have been an economy model, put out for one of the electronics schools ?

Good luck.
-Chuck


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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Mon 25, 2019 9:03 am 
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Joined: Jun Sat 09, 2007 8:14 am
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Location: Florida
That VTVM appears to be the same as one I bought on eBay ten years or so ago. I never found a model number and wound up tracing it out to come up with a schematic. It's basically an ordinary VTVM with added circuitry for the capacitance scales. The probe on mine comes apart; with a basic straight-through section for AC, Ohms, Capacitance, and a removable part with a 10 meg resistor for DC.

It operates the same as any common VTVM [the capacitance mode is used the same as is done for Ohms (short to zero, open for full-scale, etc.)].

RRM


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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Mon 25, 2019 12:42 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
You can always draw your own schematic, and we could help you from there. Or you can spend $35 and get a working one at a flea market. :). Or even less, at a swap meet or hamfest.

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https://www.bbtvtestequipment.com


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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Mon 25, 2019 6:52 pm 
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Joined: Jan Mon 17, 2011 8:57 pm
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I think it is the “83 F 120” model shown in the 1955 Allied catalog:

http://www.alliedcatalogs.com/html/1955-140/h090.html

Note that in the 1955 catalog, they use the old style front faces. By the 1957 catalog, they were using the newer looking face, and added a connector where the on/off switch is, among other changes, and renamed it “83 Y 125”. The 1956 catalog is missing from that site, but I suspect that would be the year your model is from.

1957 “83 Y 125”:

http://www.alliedcatalogs.com/html/1957-160/h197.html


Edit: Found the 1956 catalog on American Radio History’s website. That VTVM was the new version. Interestingly they were calling it the “83 F 125”.

So I’m guessing your VTVM was only made for a few months as they transitioned from the old face style to the new one, circa mid1955-early1956.

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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Tue 26, 2019 1:44 am 
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:shock: Okay, it does not have a circuit board, the tubes are 6AL5 and 6SN7, it does have the removable 10 meg tip.


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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Tue 26, 2019 2:13 am 
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That seems to match up with the 1955 version (83 F 120).

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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Tue 26, 2019 3:47 am 
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Yep, It seems to be a 83 F 120model, and all I can find was this schematic. Does anyone know of a more clear schematic that's available :?: If not, this will have to do :!:


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knight_83-120_vtvm_sch.jpeg_1.jpg
knight_83-120_vtvm_sch.jpeg_1.jpg [ 143.75 KiB | Viewed 1254 times ]
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 Post subject: Re: Knight VTVM model??
PostPosted: Feb Tue 26, 2019 4:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Seattle WA US
While Electrotanya's website is a pain to use because of the advertising/sales material imbedded in it, the schematic is a good scan. Unfortunately the schematic is presented in inverted mode, white lines on a black background. If you don't know how to deal with this send me a pm.

-Chuck


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 Post subject: Re: Knight VTVM model??
PostPosted: Mar Sat 02, 2019 10:02 pm 
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Can anyone point me in the right direction as far as a calibration procedure on this 83 F 120model ? If I switch to capacitor check, the needle goes somewhere about the middle, if I switch to resistance, the needle doesn't quite go where it should after installing a new "C" battery in the circuit. When I try and zero the meter and max the meter by touching the leads together and then opening them up, then checking say a 150 ohm resister, the needle is off a little (might read 170 ohms) and if I adjust it to say 150 ohms it doesn't go all the way back to fully open or if I short the leads it does't quite make it all the way back to zero.


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 Post subject: Re: Knight VTVM model??
PostPosted: Apr Sun 05, 2020 9:26 pm 
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Hey everyone, I'm back at this vtvm and I can't get it to work right! I'm able to get zeroed, but then I can't get my res/cap adjustment to go to infinite. I've double checked my recap job and resistors I replaced, also I checked the 2 tubes and everything looks okay! What could I be doing wrong? Could I have a bad meter? The meter does like to stick a lot! When I connected the Japanese 1MA meter, I do get the full range.


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DSC01937.JPG
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DSC01938.JPG
DSC01938.JPG [ 147.97 KiB | Viewed 639 times ]
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 Post subject: Re: Knight VTVM model??
PostPosted: Apr Sun 05, 2020 9:30 pm 
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Here Is the new Japanese 1MA meter.


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DSC01940.JPG
DSC01940.JPG [ 149.43 KiB | Viewed 639 times ]
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 Post subject: Re: Knight VTVM model??
PostPosted: Apr Sun 05, 2020 9:37 pm 
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The schematic for the Knight 83 F 120, thanks to Chuck and Vince!


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knight_83F120_vtvm.jpg
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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Sun 05, 2020 10:12 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 4019
Location: Florida
Here's how I test meter movements.

I use a little calibration klooge I made up years ago. It consists of a nine volt battery, a switch, binding posts, a 10K pot (ten turn but ordinary will do), and a 1K resistor. The pot is across the battery and the 1K resistor is connected to the wiper. This gives a max output of 9V @ 9 ma. If you use a 1.5 volt battery the max out is 1.5 volts and 1.5 ma. I mounted everything on a board with a piece of Masonite for a front panel.

To check a movement you connect the output of the klooge to the movement in series with a DMM. Start with the voltage set to zero and slowly increase it. This lets you observe the swing and check full-scale current.

RRM


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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Sun 05, 2020 10:28 pm 
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Retired Radio Man"]Here's how I test meter movements.
To check a movement you connect the output of the klooge to the movement in series with a DMM.
Like this? You mean my VTVM suspect meter?


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scribble.jpg
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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Mon 06, 2020 12:31 am 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
Here's a writeup I did on testing meter movements. It goes through all the how's and why's, and shows how to using either a variable power supply, or a fixed one. SAFELY test them. Pretty much the same as what's posted above but with a long winded explanation if you are curious as to WHY it's done the way it's done, so you don't burn out the meter under test.

https://www.bbtvtestequipment.com/testing-a-panel-meter

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Last edited by Barry H Bennett on Apr Mon 06, 2020 1:49 am, edited 1 time in total.

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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Mon 06, 2020 1:15 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 4019
Location: Florida
ychris wrote:
Retired Radio Man"]Here's how I test meter movements.
To check a movement you connect the output of the klooge to the movement in series with a DMM.
Like this? You mean my VTVM suspect meter?


Yes but with a DMM set to current in series with the analog movement so you can monitor the current. Be very careful to start with the voltage set to zero. You can use a 1.5 V battery to lessen the maximum current to 1.5 ma. That will be safer in case you forget.

RRM


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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Tue 07, 2020 12:41 am 
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Like this? I'm going to have to get a 5k pot, I don't currently have one. :D


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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Tue 07, 2020 1:06 am 
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Joined: Nov Wed 30, 2016 7:35 pm
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Location: Sunbury, Ohio 43074
It doesn't have to be a 5k pot ... anything close will work. Check out the link I sent you above and you'll maybe see a little clearer what it is you're attempting. I didn't get my drawings done yet, but yours is fine.

You might want to increase the 100 ohm a bit until you see what range you're in .... you can always lower it later if needed. Protecting the meter under test is what you're after.

_________________
Preserving the hist. of electronics, one boat anchor at a time! :)
https://www.bbtvtestequipment.com


Last edited by Barry H Bennett on Apr Tue 07, 2020 1:07 am, edited 1 time in total.

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 Post subject: Re: Knight VTVM model 83 F 120 won't cooperate!
PostPosted: Apr Tue 07, 2020 1:07 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 416
Location: Missoula, MT
Some of those big plastic meter faces will build up a static charge and screw up the needle motion. Try wiping the plastic with a dryer sheet or a microfiber lens cloth.


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