Newer schematic for 500-C 7n,nnn serial numbers?

[thornev]

It looks like there are several different resistor values in my 500-C serial number 76944 receiver. R114 and R116 state in the 30001-49999 schematic to be 68K, but mine both read 53K on the multimeter. I'd ordinarily say that the resistors need to be replaced, but not when both read the same value. Too much of a coincidence.

Another example is R113 and R115. Schematic reads 180K, but my two are 73K on a multimeter.

I suppose it's possible that previous owners changed these resistors. I have no way of knowing. But since the last 500-C schematic I can find goes up to only 49999, that leaves out all the 50000-79999 serial numbered units.

Anyone have insights? Thank you.

 

[larryderouin]

Read the Stripes on the Resistors. Also if you are reading them in circuit they all will probably read low as you're reading in the whole circuit. Either read off the stripes, or post pics here, or pull one leg off the circuit and read again.

 

[thornev]

Would someone please tell me the ohmage on the 4 resistors in the attached picture and explain how you read the stripes? I'm unsure about which stripe is the multiplication stripe and I'm not sure about the colors. I get confused between orange, red and and brown, and between silver and grey especially when the colors start to fade. I guess gold appears only as the last stripe which is the multiplier, but I'm not sure which stripe is the multiplier - the outer last or the inner last, or is the stripe on the fatter part of the resistor? Thank you. Thorne

 

[RUmad]

The two in the middle are 470k @ 5%
I can’t tell the colors on the others
Multiplier is the one closest to the tolerance band.

Edit, I take that back. Seeing it wrong. The second from the right is 470k. Not two of em. Kinda hard to see the colors.

 

[larryderouin]

On a 4 stripe the 1st two are numbers. The 3rd is the multiplier and the 4th is the tolerance (5%gold or10%Silver). I assume these are on the 500c. Pull out the picture a little so we can see where they are in the circuit and which tube socket they are near.

The colors are number coded 0 to 9 as follows
Black 0
Brown 1
red 2
Orange 3
yellow 4
green 5
blue 6
violet 7
grey 8
White 9

OR! As I learned it in High School (back in the 60's / 70's)as did a lot of ET's in the Military.
Bad 0
Boys 1
Rape 2
Our 3
Young 4
Girls 5
But 6
Violet 7
Gives 8
Willingly 9
Same numbering but it sticks faster.

This goes for the 1st, 2nd, and 3rd stripes on the resistor from the EDGE IN. The 4th stripe will either be SILVER (10%) or GOLD(5%) in 90% of the cases. Very Rarely you'll see other tolerances with the most prevalent a 1% (BRN) 2%(RED).

5 stripe resistors are not as prevalent as 4 stripe resistors and are read slightly different. I won't go into that here. But the Resistor Color Code Resolver does 5 stripe calculations .

L

 

[larryderouin]

And get a resistance program. I use this one. Resistor Colour Code Solver from abk Freeware. http://myfreewares.weebly.com/resistor-colour-code-solver.html

 

[nj pheonix]

The way I learned it in electronics shop
B BAD BLACK 0
B BOYS BROWN. 1
R RAPE. RED 2
O OUR ORANGE 3
Y. YOUNG. YELLOW 4
G. GIRLS GREEN 5
B BUT. BLUE. 6
V VIOLET VIOLET 7
G. GIVES. GRAY. 8
W. WILLINGLY. WHITE. 9

Probably politically incorrect today
I did remember it for nearly 40 years so it must be worth something.
Honestly lately I use this
https://www.digikey.com/en/resource...version-calculator-resistor-color-code-4-band

 

[nj pheonix]

Oh, btw
They look original to me.
There were documented and undocumented on the flu changes during production

 

[larryderouin]

on the flu changes

Really Andy! We;ve got enough problems with the Asian Flu, Spanish Flu, and now you want to spread FISHER FLU????

 

[audmod01]

You won't likely see them in Fisher equipment, but resistors with no tolerance band are 20% tolerance. I would also mention that the original banding practice in carbon composition resistors had the first numerical band right at the end which indicated that was the band to begin to read from with other bands following in sequence. Some issues are presented by having a body color that is close to one of the standard band colors. For example a redish-brown background or a blue background. It makes determining the band values difficult, especially with age or possible overheating of the resistor. Another color change comes from air contaminants such as cigarette smoke or from cooking oils etc.

Larry is right about measuring resistors in circuit. They seldom read as marked when measured that way due to parallel paths through other circuits connected in parallel with the one you are measuring. The best way is to disconnect one end of a resistor in question. If a resistor is especially difficult to read and the band colors are faded, it may be an indication that the resistor has gotten so hot it has changed the color of the bands badly. Look for problems in the circuit in which it is located for conditions that could cause excessive current through the resistor.

Most of the resistors of the type you illustrated in the picture you posted are seldom off value by any appreciable amount. Fisher used good quality resistors that seem to be better than most. They are a type of film capacitor. Carbon composition resistors have the sharply delineated ends. The Fisher resistors usually have the redish-brown background and have somewhat ball shaped ends. The resistors that tend to change the most are carbon composition high values - those approaching 100K ohms and higher.

Joe

 

[fred soop]

It also helps to know the standard values. If your guess on the colors is not a standard value, then it is more likely to be wrong. The values in the above photo appear to be 68K, 180K, 470K, and 33K.

Note that there are 2 types of 5 stripe resistors. 1% resistors will have 3 digits, a multiplier, and a tolerance. Some resistors, MIL spec I think, may have a yellow stripe as a 5th stripe. This has nothing to do with the value.

 

[Tim D]

The way I was taught many years ago was:

B BAD BLACK 0
B BOYS BROWN. 1
R RACE. RED 2
O OUR ORANGE 3
Y. YOUNG. YELLOW 4
G. GIRLS GREEN 5
B BY. BLUE. 6
V VICTORY VIOLET 7
G. GARDEN. GRAY. 8
W. WALLS. WHITE. 9

Sounds like a WWII diddy. I was also learning it in High School Electronics, so they needed to keep it "G-rated". The High School teacher was an old AF guy from the 50's. The guys only understood tubes, so back then I had some tube basics. I took 3 years of the stuff in HS. Actually, had to self-teach myself solid state from books during that period. Built a Fender tube amp from scratch with a diagram. I had to buy the trannies though.

 

[Tim D]

I recently checked every single resistor in my KX-100 amp and any that read low, I then disconnected one end and remeasured to retest out-of-circuit. Here's how I did it.

1. Made a spreadsheet from a parts list from the service manual of just the resistors. Used the diagram in the service manual and the color code to find the correct resistor in the unit.

2. Converted the resistance value for each to the color code to make each one easier to identify. (This became another column in the spreadsheet.)

3. Measured every resistor in-circuit. (And the measured value became another column (or two if there were right and left channel twins). If any read significantly below what was expected, then I disconnected one end of the resistor and measured again. I ended up finding about a half a dozen out of spec resistors this way that I replaced in my KX-100. Note that disconnecting one end of the resistors can be a pain, but with patience you can do it.

Many resistors can be read in-circuit because there are no other paths across the resistor. In general those that read close to their intended values can be measured this way. I was able to measure more than 75% in-circuit. You will invariably find some that read low in-circuit and that can be for one and/or two reasons. Those are:

1. There is another circuit (or circuits) in parallel with the resistor and you are reading the combination resistance of the resistor and other components. AND/OR
2. The resistor is just plain bad.

After you measure each one you can then compare the intended value with the measured value to determine if the resistor is too far out of tolerance. While doing this you can visually inspect each to see if they look cracked or heat stressed and can then put notes in the spreadsheet to replace them later.

NOTE: As a second activity I (later) measured the voltage across each one and calculated the power dissipation based on ohm's law. I ended upgrading the wattage on a couple of the resistors because they were dissipating enough that I thought it worth while to add a safety factor. (The voltage and power became additional columns in the spreadsheet.) I did this all in an afternoon. This might be a good rainy day activity. Be careful of the high voltages though.... Safety first!

 

[thornev]

Andy - "flu" ???

I'm glad I'm not the only one who cannot read those resistors.

Tim - I have 149 resistors in my 500-C. How many do you have?

 

[Tim D]

Thorne,

There's about 75 resistors in the KX-100/X100B.