Resistor values - Videokarma.org TV - Video

Daniel6co · #1 01-17-2021, 12:22 PM

So I am discovering that I have replaced a bunch of resistors in my 1957 Silvertone Medalist with incorrect values. What Is confusing me is that the parts list identifies some resistors as for example 4.5 ohm and other written out as 4500 ohm... am I crazy or isn't 4.5 the same as a 4500? I am finding that several of the resistors that I replaced which denoted with the decimal point are incorrect, and when the original is placed back in the set the performance keeps getting better. Maybe I should have ignored the resistor value list and just replaced based upon what I actually pulled from the boards? Or am I way off here?

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init4fun · #2 01-17-2021, 01:29 PM

Quote:

Originally Posted by Daniel6co

So I am discovering that I have replaced a bunch of resistors in my 1957 Silvertone Medalist with incorrect values. What Is confusing me is that the parts list identifies some resistors as for example 4.5 ohm and other written out as 4500 ohm... am I crazy or isn't 4.5 the same as a 4500? I am finding that several of the resistors that I replaced which denoted with the decimal point are incorrect, and when the original is placed back in the set the performance keeps getting better. Maybe I should have ignored the resistor value list and just replaced based upon what I actually pulled from the boards? Or am I way off here?

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First off , yes indeed 4.5 ohms is NOT the same as 4500 ohms , and if you made similar mistakes on other resistors you'd best check every one you replaced for being the wrong value . As to what's in the set VS whats on the list , since production changes didn't always make it to the parts list I usually defer to the actual indicated values in the set , and of course only replace those who are out of tolerance .

Hey , no biggie , mistakes happen especially when doing the first few sets , just consider yourself lucky you haven't fried any hard to find parts (coils & such) and chalk this one up as a learning experience ....

Kevin Kuehn · #3 01-17-2021, 01:30 PM

Generally speaking it's best practice to read the value off the old component and replace with same. Unless of course it's obvious that someone was in there previously not knowing what they were doing. Also Sams photo facts were notorious for having typos.

Daniel6co · #4 01-17-2021, 05:26 PM

Thanks guys, yeah this set was pretty much untouched except for a couple replaced caps from way back, im trying really hard to not be that guy we all curse out who owned it last 🤣 I figured out my mistakes and the set is playing really well now! Guess I need to slow down and triple check my work!

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bandersen · #5 01-17-2021, 06:36 PM

4.5K is the same as 4500 ohms. 4.5 ohms is not. Are you looking at the Sams Photofact, Riders or something else ?

Daniel6co · #6 01-17-2021, 07:09 PM

I'm using a sams schematic. In my mind I defaulted when I saw resistors listed at 4.5 and such to mean 4.5k since modern resistor are labeled as such, but as I found out the resistors that are actually in the thousands of ohms are written out. I jumbled it all together in my brain. Thankfully I didn't fry any major components, just had a really dim raster 🤣🤦&zwj;♂️

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Electronic M · #7 01-17-2021, 10:04 PM

Original resistors were labeled in color code, and many new resistors are available with the same color code on them. Taking time to read (or learn to read) color code is worth while if you plan to work on more than one electronic device in your life.

Always try to read the original markings/color code on any original looking part you change...I've neglected to do that early on in my time in the hobby and had Sam's typos bite me in the ass a few times (it's worst when you move residence during a restoration and lost the old parts so you can't figure out what the original was)... you'd be amazed at some of the dumb mistakes people that drew schematics have made.

Yamamaya42 · #8 01-17-2021, 10:33 PM

As it's been stated in many threads, many times, only replace resistors that are out of tolerance, WHAT that range of tolerance is generally up to the tech, I prefer to replace ones that are %15 or more out, some say you can get away with %20, and YES, sometimes there is errors in the SAMs, but this is rare,
and it's always good to replace a few parts at a time, and test to see if you broke anything.

MY method for replacing resistors is to find the target area on the SAMs, locate the resistors there listed, and if they are out of tol, replace, and as Electronic M said, make sure what you are checking matches what is on the SAMs via color code, AND, when replacing, I also measure what I am putting in for extra safety, I want to make sure the new one is correct, ( IE was made wrong or defective )
You can't check and re-check too many times...

Kevin Kuehn · #9 01-17-2021, 10:46 PM

To confuse matters even worse some really old schematics from the 1920's through something like the mid to late 1930's used M instead of K to designate the 1,000's multiplier. If in doubt lift one end from the circuit and measure. At least then you'll know where you need to be in the ballpark.

Electronic M · #10 01-18-2021, 08:03 PM

In most restos I replace resistors last and usually only do it if I'm seeing performance issues or outright malfunction....In that case the marked tolerance of the original part is usually a hard limit (I might tolerate an extra %1-3 if it's burried or connects to something delicate like a coil terminal. I might be more generous if I'm just indescriminantly checking resistors but that is usually my MO.
Marked tolerance varies by application and era. In the 20s and 30s %20 was the most common tolerance and %10 or tighter was for special or precision stuff. The 40s %10 was coming in to dominance, but many TVs had a few %5 in them in important areas. By the 70s %5 seemed to be the standard.
Always watch the original tolerance if you are checking everything for %10 including that one critical %5 that clocks in at 9 then you are missing issues.

I think I have found around 5-7 different Sam's errors (and I know of many more others have found) 2 of which caused me to make sets worse off than what I started with, forcing me to work extra hard to get back to normal. While that's only about %5 of the sets I've worked on, its still enough that I try to ensure that I'm not about to labor under a typo (or the more common undocumented production change) before I change something. The best mistake is the one you realize and stop your self from making before you do it.

Daniel6co · #11 01-18-2021, 09:11 PM

Really appreciate everyone's input here. When I started out with old radios a few years ago I was one of those guys who just replaced caps and cleaned them up. Now I'm always trying to take my next project and learn more and more each time. Schematics were Greek to me but now I'm getting pretty good at following them along and learning to troubleshoot. Vintage tvs have definitely pushed me further and I am really enjoying the knowledge they are giving me.

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