Resistor Question?

tube-a-lou

Addicted Member
Hi all,
I've been working on a 1953 Fender Deluxe amp and it had in the amp originally
250K resistor's about five, I was able to find 240K and put them in. Now I found a stash
of what looks like the original resistor's that Fender used way back when but they are
270K's. What if any will a difference in sound be?


5B3 (1).jpg
 
Not sure what the sound difference will be, if any, but the tolerance on equipment of this era was typically 10% for the resistors. If so, this means +/- 25K against the original value of 250K, or an 'in tolerance' span of 225K to 275K. The 240's are actually quite close, within 4%, so why change?
 
The look of the amp, worth more if it has the original parts in it or close to it. The guitar
world is different than the audio world!
 
The 270k for the plate loads will slightly increase gain and distortion. In the paraphase section it may cause a more unbalanced phase invertor, again more distortion.
 
measure the 240Ks, and the 270Ks, use the ones that are period correct for
value preservation and closest to 250K. then document it for when you sell
to someone more fussy than you about period correctness and will scream
when he finds out it's not an original 250K.
 
And onother practical consideration: Consistency of tubes.

I may have mentioned before that these days it is not seldom to find a spread in same number tubes of some '- 30% to + 30%. That makes a few percent change in resistance value of lesser consequence.
 
If I go by the schematic the 250K's are by the first preamp tube and the second phase
inverter tube both are 6SC7 tubes.
 
It's tough to see from the pic. They just look like carbon comps. How do they test.
Being how noise and distortion aren't necessarily the enemy here, perhaps you should just leave them
 
Hi all,
I've been working on a 1953 Fender Deluxe amp and it had in the amp originally
250K resistor's about five, I was able to find 240K and put them in. Now I found a stash
of what looks like the original resistor's that Fender used way back when but they are
270K's. What if any will a difference in sound be?


View attachment 1186739
If you are replacing the originals with carbon comps of the same wattage, only a techie who is a Fender junkie would realize that you switched from 250k to 240k. There should not be any difference in sound from the amp as you are within the tolerance factor. So, why worry? Be happy! regards.
 
Hey Lou,,, Its possible the stash of resistors you found are as old as the ones in the amp... Also very possible they are out of value as much as the originals... If the 240K and the 270K are both in value (which I doubt), they are more than 10% different... If it were me and I wanted to swap resistors, caps, etc in a vintage amp that had value because its untouched and has original parts,,, I would use modern, close tolerance parts and save the originals for a future owner,,, or just leave it alone, if you really want it exactly as Fender made it!!!!
 
True, the amp was restored in the late 80's and all the original 250K resistors were all
changed to 220k resistor's. I found a few of those 270K resistors that look liked the ones
Fender used back in the 50's I measured them and they measured between 269K to 280K.
In the mean time I found Allen Bradley 240K's resistor's which are in there now. It's really
a bit in my part of experimenting with amps and different sounds.
 
I have swapped out old parts for new shiny parts, only to find the old crappy parts have the mojo....mostly liking carbon comp resistors and old blue molded Ajax signal caps for Fenders. I've tried many electro's for the power supply dog house and didn't notice a difference... my 2 cents....
 
Those Blue Molded and Yellow Astron's have a following more so for the Blue Molded they are
said to hole up well though the years and sound good.
 
The Blue molded fender caps are almost always good. In fact, I don't think I have ever tested a bad one.
The yellow Astron's are 50/50 though. Those Red paper label caps are almost always bad .
The dominoe mica cap is almost always good and very good sounding.
I don't think the value is hurt too badly replacing Carbon Comp resistors with Carbon Comp, even though the newer ones are smaller than those early ones in your amp. If you want them to look closer to the original ones you could use 1 watt. The carbon comp do sound the best though if they are not noisy.
Wholesale replacement with metal film and orange drop caps does hurt the value and tone quite a bit.
 
You didn't specify which model board it has. So I have to assume it's either the 5A3, 5B3 or 5C3 because after that, they re-designed the amp and used different tubes and therefore different parts.
The plate resistors in a phase inverter are somewhat critical as to their matching abilities. Looking at your photo and following the Fender assembly diagram, those two resistors look like they have no tolerance (4th) band. So they are +/-20% or 200-300k Ohms. I would use the 240k's you have but hand match them using an ohmmeter to as close as possible. Even if the parts were 5%, that would still be 238-262K Ohms, so the 240ks would work as long as they are at least 238k. This won't adversely affect the sound.
 
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