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 Post subject: I-177B Tube Tester
PostPosted: Mar Fri 09, 2018 5:28 am 
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Joined: Apr Fri 14, 2017 3:03 am
Posts: 52
Location: Dallas, Texas
Rebuilding I-177B tube tester and have question regarding the replacement of the below bad resistors. Are the below resistors 2-watt with the exception #43 and #45 they seem to be 1/2-watt. Thanks

Loc # Val Tested

#40 - 1.2K - 1.483K
#41 - 15K - 14.24K
#43 - 180K - .01 ohms
#45 - 5.1k - 0.1 ohms
#78 - 30k - 23.37
#79 - 51k - 27.05k

p.s. I did see reference to a 8-watt resistor on the schematic, but have not got to that resistor yet.


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Fri 09, 2018 5:51 am 
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Joined: Sep Wed 04, 2013 2:23 pm
Posts: 680
Location: Atlanta, GA
You're going to get some good advice from many folks, I'm sure. Let me just ask IF you disconnected one of the ends of each resistor before you measured them? If not, do it all again and make certain what you think needs to be replaced, really does need to be replaced because it's out of tolerance. I've been down that road before and learned hard lessons... Spool resistors? Careful!! I've learned that working on an old radio is one thing, and a tube tester is another. I take whatever I want fixed/calibrated to someone I trust... and I don't trust myself! :lol:

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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Fri 09, 2018 12:59 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 1210
Location: Sunbury, Ohio 43074
My advice is ... proceed with extreme caution. I would absolutely advise against replacing resistors wholescale in a tube tester. As noted, before you even consider doing so you need to disconnect one end of them to measure them with assurance that they are not being shunted by something. How accurate is your meter, and what is the tolerance of the resistor being tested, are other factors to consider.

Take your #53, #45, #78, and #79 for example ... resistors seldom, or in my experience never, decrease in resistance with age.

A second consideration is some of those resistors *may* have been selected at manufacture to bring the instrument into calibration. I'd replace the capacitors, clean the switches, and then see if it calibrates properly before starting on resistor replacement unless you have tested them as indicated above. Even then, if they are within a few % of stated value, I'd leave them alone unless replacement is indicated during calibration.

And as also noted, if any of them are spool resistors, the only thing that is likely to go wrong with them is that a wire will break where it's connected. They are simply a length of selected wire on a bobbin and while I suppose they could short or open internally, it's quite unlikely unless the tester was abused somehow.

just my $1.33 :)

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He who dies with the most sheer tonnage of ancient test gear, wins!


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sat 10, 2018 10:53 pm 
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Joined: Apr Fri 14, 2017 3:03 am
Posts: 52
Location: Dallas, Texas
Took the #40 resistor out of the tester today it should be 1.2K it tested at 1.512K way over specification. I do understand that the unit has a calibration procedure and that can account for differences in resistance. However, what I don't understand is how can the calibration account for that value being that far off. The reason I pulled the cover and embarked on this process is that I have a tube that read bad ran it on my buddy's two tester's turns out the tube is good. Also, the line calibration seems to wander too much.

My original question was what is the wattage of the resistors in the I177-B and what I received back responses do not do anything and do the calibration. My thought is replace the out of spec resistors and then calibrate. Any thoughts. Thank you.


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sun 11, 2018 12:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10506
Location: Latham NY
I have used and repaired 177 tester for years. I don't recall seeing any wattage values listed in any service lit. Post a pic of the resistor and maybe we can make an educated guess. If the tester does not work right the first thing I do is take readings of the plate, screen, grid bias and signal voltages and go from there.


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sun 11, 2018 12:35 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11553
Location: North of Mpls, Minnesota
The spool resistors should have the value written on the end of the spool, they usually do not match the schematic and are matched to the unit.

Dave


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sun 11, 2018 12:44 am 
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Joined: Apr Fri 14, 2017 3:03 am
Posts: 52
Location: Dallas, Texas
I would post an image of the resistor but my camera on my phone is busted. The resistor Brown, Red, Red, and Gold 1.2K resistor not sure if its a 1, 2, or 3 watt. Is there a place where I can view the parts list for a I-177-B. Thanks.


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sun 11, 2018 1:10 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 11553
Location: North of Mpls, Minnesota
http://www.mzentertainment.com/pics/tes ... matics.JPG

http://www.radiomanual.info/schemi/Surp ... 7_1945.pdf

Dave


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 Post subject: Re: I-177B Tube Tester
PostPosted: Mar Sun 11, 2018 6:12 am 
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Joined: Apr Fri 14, 2017 3:03 am
Posts: 52
Location: Dallas, Texas
Thanks most are 1-Watt with several 1/2-Watt


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