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 Post subject: Resistor replacement
PostPosted: Apr Sun 22, 2012 1:44 am 
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Joined: Apr Sat 21, 2012 9:07 pm
Posts: 5
Hi,
I'm new here and glad to be part of this forum.
I am rebuilding a Sprague TO-3 Cap Tester which was worked on before I received it.
This tester probably goes back to the 1950's era. It has large size resistors, possibly some not original. Numerous resistors are way out of ohm spec's (tested by ohm meter) and ohm values shown by an updated schematic. Only a few wattage amounts are given for specific resistors. If no wattage or tolerance resistor values are given, what replacements do I order? The schematic states that resistors shown with an "S" with it denotes a Range Standard, whatever that means??
This tester provides 750 Volts (need for proper resistor wattage), and being it is a tester (need for proper resistor tolerance) for testing accurately.
Any help greatly appreciated on this matter.


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 Post subject: Re: Resistor replacement
PostPosted: Apr Sun 22, 2012 1:59 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Albuquerque, NM 87123
Can you supply a photo so we can get an idea of the size of the resistors?


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 Post subject: Re: Resistor replacement
PostPosted: Apr Sun 22, 2012 4:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5875
Location: Cleona, PA
This website gives photo size comparison of resistors.

http://www.philcorepairbench.com/resistcompare.htm

_________________
Reece


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 Post subject: Re: Resistor replacement
PostPosted: Apr Sun 22, 2012 6:44 pm 
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Joined: Apr Sat 21, 2012 9:07 pm
Posts: 5
This is a photo of the different size resistors on side of the wafer Selector switch

Image

This photo is of the Meter Range wafer switch

Image

My idea is to place new resistors with wattage the schematic shows, but the other resistors (wattage not given) I would like to keep uniform (say 1/2, or 1 watt) as much as I can to get (say 1% or 5% tolerance) of resistors allowing more accuracy from the tester. Being this is an old tester with high voltage, evidently wattage overrules low tolerance for the resistors. But what is the wattage standard recommended for the remaining resistors :?:
Again, glad for any help given.


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 Post subject: Re: Resistor replacement
PostPosted: Apr Sun 22, 2012 7:25 pm 
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Joined: Nov Sat 27, 2010 6:15 pm
Posts: 4848
The 22K is a 2 ewatt, rest of the little ones 1/2 watts, but I would use 1 watters if I had them. Modern equivalents much smaller.

Most of ;em would have drifted way high, so get them all replaced as well as ALL the caps.


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 Post subject: Re: Resistor replacement
PostPosted: Apr Sun 22, 2012 7:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7656
Location: Minnesota
Most of your resistors are going to be 1/2 watt, larger ones will be marked on the schematic.
It will not be necessary to replace the wirewound resistors as long as they test good, they
will be either good or bad, they do not drift. The range resistors and caps should be 1% or
it will be difficult to calibrate. It looks like some of the resistors and caps have already
been replaced.

Dave


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 Post subject: Re: Resistor replacement
PostPosted: Apr Mon 23, 2012 3:26 am 
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Joined: Apr Sat 21, 2012 9:07 pm
Posts: 5
On the schematic it shows an S after a couple of cap values and after 3 resistor values on wafer switch plate 2F (upper photo), same on some resistors for wafer switch plate R (lower photo). Other caps and resistors on the schematic don't have the S. The schematic denotes S as Range Standard, what does that mean??


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 Post subject: Re: Resistor replacement
PostPosted: Apr Mon 23, 2012 4:18 am 
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Joined: Oct Wed 29, 2008 1:47 am
Posts: 343
Location: Ashburn, VA
The wire wound potentiometer is shot (frayed wires in pic) and must be replaced... Not sure what wattage that would be


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 Post subject: Re: Resistor replacement
PostPosted: Apr Mon 23, 2012 5:44 am 
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Joined: Apr Sat 21, 2012 9:07 pm
Posts: 5
Yes, I have a 50K ohm, 50 watt pot ordered at a good price. The original pot is 50K ohm, 15 watt, evidently no longer made. The new pot should outlast the components in the tester if used properly. Meaning when turned SLOWLY to drain the charge from the cap after test is completed.


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 Post subject: Re: Resistor replacement
PostPosted: Apr Mon 23, 2012 7:19 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 7656
Location: Minnesota
spragueto3 wrote:
On the schematic it shows an S after a couple of cap values and after 3 resistor values on wafer switch plate 2F (upper photo), same on some resistors for wafer switch plate R (lower photo). Other caps and resistors on the schematic don't have the S. The schematic denotes S as Range Standard, what does that mean??



See my last post about the range caps and resistors.

Dave


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 Post subject: Re: Resistor replacement
PostPosted: Apr Mon 23, 2012 1:42 pm 
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Joined: Apr Sat 21, 2012 9:07 pm
Posts: 5
Ok Dave, now I Know what Range Standard means. Thanks.
Also, Thanks to all for your input so I can get this tester back to normal working condition. I appreciate your help.


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