How Much Difference Can 10 OHMS Really Make???

[Nostalgic Distortion]

Howdy everyone!!! So I’ve got a quick, mostly hypothetical question for you..

This f-ing gem is my Ampeg J12-D, I picked it up a couple weeks ago (In much worse shape than you see here) for $100 from a local guy..

Originally I bought it because it still had its original tubes & I know what the stupid 6KB11 & original 7591’s can sell for, sometimes a hundred bucks a piece!!!

I thought worse case scenario I’d get my money back on those alone, but then I plugged it in after getting it home and clean I plugged it in long story short, I like it & now I wanna keep it!

However as you can see it needs some love!!! I’ve already replaced the cord, Etc., & now I’m about to turn my attention to the filter can & turret board.

Heres my question...

If you look to the right of the board you’ll see a couple 10W resistors. The one further to the right is a 1K, and the one to the left (the one that looks like a leftover roach from a Cheech and Chong movie) is 140 ohms.

Now 140 ohm 10W resistors are not super common theses days but they can be found. Now on hand I have some Ohmite 10W resistors that are almost perfect but unfortunately no 140 ohm’s...

I do have a 1K and I have a 150 ohm resistor. So could I safely get away with using these??? Now again I likely won’t end up doing it unless the general consensus is that it is completely safe, but I was kinda wondering how much difference an extra 10 ohms on this resistor would make....

 

[ehdwuld]

The resistor is there to step down voltage across some other components
changing the resistor size, changes that voltage
it would not only sound different
the lower voltage may cause something downstream to fail

You can get a higher wattage but same size resistor for pennies

Do that

 

[Nostalgic Distortion]

Yeah, I had already ordered a couple 10W 140 ohm cement resistors. They cost me $3 for two of them & I’m hoping they get her tomorrow...

 

[JMP/HBE]

10 Ohms can be the difference between a perfectly fine amp and an amp thats fried depending on application.

 

[Nostalgic Distortion]

Well as I said it was a mostly hypothetical question...

I actually had already ordered some 140 ohm resistors when I’d asked it..

Actually aside from the can capacitor that amplifier has been completely re-capped, the right resistors have been installed, Etc...

It’s currently working & sounding much better than before! When I got it I thought the tremolo circuit was pretty decent, now it’s absolutely beautiful!!!

 

[Nostalgic Distortion]

[No message]

 

[Nostalgic Distortion]

Not sure why that picture is so small but I’m happy with it!!!

 

[AlexR]

There is always a tolerance with components. The 140ohm resistor which wes in there could be anything up to 10% variable when new - unless they were specially picked for low tolerance (which is more than 10 ohms). Also age and use can make them drift further.
Obviously you try and get the closest you can.......and you can always check with manufacturer voltage specs for the closest points to where your component sits.

 

[devastone]

Measure the 150 ohm resistor, the 140 ohm probably has a +/- 10% tolerance, so could be anywhere from 126 to 154 and still be in spec. I would bet the 150 is in that range, even if it is just a hair out it will be fine. Some people freak out over this stuff, but the reality is, these components have big tolerances, and it is close einough, it is certainly not going to fry anything unless there is something else wrong.

 

[Nostalgic Distortion]

Measure the 150 ohm resistor, the 140 ohm probably has a +/- 10% tolerance, so could be anywhere from 126 to 154 and still be in spec. I would bet the 150 is in that range, even if it is just a hair out it will be fine. Some people freak out over this stuff, but the reality is, these components have big tolerances, and it is close einough, it is certainly not going to fry anything unless there is something else wrong.

This was actually one of the first things I tried. I was kinda hoping it would measure up a bit low, perhaps in the 143-145 ohm range?

Unfortunately both of the 150 ohm resistors that I had read out at pretty much exactly at 150 ohms...

Really this entire topic came up because I was trying to do my best at keeping the big ugly, 10W cement resistors off the circuit board board, hoping to be able to use the much nicer looking Ohmite’s instead...

So the question had absolutely nothing to do with the amplifier’s sound, or the quality of the component. It was purely because the offended my sensitive aesthetic sensibilities...

 

[AlexR]

Well, that is pretty sensitive to be sure.....especially given its something you'll never see unless you're replacing a component (which could be never again for you).

I don't know about the properties of cement resistors, but they seem to be common in high wattage applications.....maybe a good reason for this don't you think??

 

[Nostalgic Distortion]

Well, that is pretty sensitive to be sure.....especially given its something you'll never see unless you're replacing a component (which could be never again for you).

I don't know about the properties of cement resistors, but they seem to be common in high wattage applications.....maybe a good reason for this don't you think??

Exactly...

 

[devastone]

Well, the 150 would work, but apparently not aesthetically pleasing... Should be able to order a few 150s in the kind you like and measure them to find a value that is close.

 

[Demanic]

Exactly...

Lol, it's almost like worrying about how spark plugs look.

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