Tube Amps / Music Electronics
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|9/3/1997 12:54 PM|
Would anyone know a good source for Allen-Bradley carbon composition resistors? I've found them in Newark electronics, but they have to be purchased in multiples of 50 of the same value.
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|9/3/1997 10:36 PM|
How many of what value do you need?
I have aproximatly 96,000 AB resistors in my
shop and maybe I can spare a few.
|9/5/1997 10:30 PM|
Jason, I'd take Bruce up on his generous offer. You see, A/B is no longer in this business!
I work for the last A/B distributor and last fall was the cut-off for final "lifetime" orders. We have about $10 million worth of stock but unfortunately my company can only sell in volume so there's no point in listing their name.
A/B were the last people making carbon comp resistors, except for a few Far East mfg's that make "super cheapo" styles that will break if you breathe on them...
Although purists will argue about tone quality the mainstream electronics industry long ago moved to carbon film and now metal film technologies. Carbon comps were really poor resistors! They changed value with age, heating and even humidity! The only thing that kept A/B in the game this long was that many military mfg's still bought to old part numbers. The price on these things had gotten to be over 10 times that of a more modern resistor but of course military people have little concept of cost-effectiveness!
Frankly, I don't believe that replacing with carbon or metal film will have any difference on sound. The critical parts are the caps...you have to stick with film styles and NEVER use a ceramic!
Now that I've ruined your day...
|9/8/1997 9:42 AM|
When I measure carbon comp resistors in 30-35 year-old amps, I usually find that their values have drifted up, sometimes well above the upper tolerance limit. It seems that 100K plate resistors almost always measure around 110K or more.
Although Dan Torres has been rapped pretty hard in this BBS (and, yes, his book does have its faults), I do have to wonder if his theory about drifting carbon comps has some merit. He claims that the reason older amps with original components may seem to sound warmer and browner has nothing to do with the TYPE of resistor that's in it; it's just that the preamp gain stages each have slightly more gain and compression due to the actual 110K-120K plate load resistance on them (vs. 100K in the schematic). Supposedly, this "good old" sound can be recreated perfectly well by using modern 110K 1% metal film resistors (along with using 1K8 metal film resistors instead of 1K5.
Any other opinions on this? I would be especially interested in hearing from anyone who believes that carbon comps DO make an audible difference that stems from their inherent physical properties. If this is the case, then what exactly is the sonic effect, and what causes it?
Does the fact that the resistive element in a carbon or metal film resistor is shaped like a helix mean that there's any meaningful inductance (not present in carbon comps) that we can actually hear?
|9/19/1997 1:59 PM|
I believe there IS a difference between resistor types as far as the sound goes.
I had occasion to restore a pair of early 60's Ampeg Jets recently. This was a total electronic makeover. Every part in the amp was replaced except for the transformers, even the on/off switch and the indicator light were changed. One amp got all carbon comp resistors and the other got a mixture of metal and carbon film depending on what I had in stock. Coupling caps were measured on my capacitance meter to be as close to face value as possible. When all was said and done, I felt that the one with the carbon comp resistors had a more pleasant sound. I was hoping this would not be the case for all the reasons mentioned in the previous post. I even tried running them through the same speaker to eliminate that variable. I have seen many old amps where almost all of the CC resistors were off or way off. Now I just clean them all out, and so far has been worth the effort. At least it is with amps worth restoring.
I hope to get another pair of amps in soon to gather more data. I realize this one test is far from conclusive, but there it was for what its worth.
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