WTH? NOS CC Resistors don't measure anywhere close to stated values!?!

[R.G.]

Several of the stages in the preamp chain can be operating at or in excess of that level when the preamp is overdriven. When using a high output humbucker, even the input stage can get close or even over that level. In some circumstances the output stage is not overloaded and the phase inverter plate resistors might only have a few volts swing. So this is a more complicated question.

That said, I do not think it is the CC resistors that make any significant difference in the sound under those conditions. Not when the tubes are overdriven so hard; they are what control the sound.

It is a complex question, and of course, that invites rule-of-thumb oversimplification - which I did.

The key to my particular oversimplification is the input range of a tube and the voltage coefficient of a CC resistor. For the few brands of CC's that I could find either current or historic specs on VCR, you get to a percent or two of distortion at 70-100V of signal swing. At lower swings, the VCR distortion is proportionately lower.

Every tube has an input range for linear-ish input. This varies from Vgk= 0 down to cutoff. For a 12AX7, this is on the order of 1.5-2V, depending on the actual tube and maker's setup. Exceed this range, or even get close to it in the cutoff direction and distortion skyrockets. In a triode's case, the distortion is at first soft compression of the peaks, which is what VCR distortion from CCs would do. While the 12AX7 can easily get to 70-100V of swing on its plate, if you feed that unvarnished into another 12AX7 grid, the grid distorts long before the signal range for CC distortion is hit.

What happens in most cases (there's that broad brush again!) is that 12AX7 stages amplify the signal up by 20-30 times, then the signal is attenuated back down by things like tone/volume stacks and such. This process certainly can get a 100V signal down to the 1V or so level that can support CC VCR distortion. It gets tricky to balance signal amplification and attenuation to generate a big signal, then attenuate it down to where it's just right for the following triode stage to highlight the CC distortion.

Except in the PI (there's that's brush again!) where the PI needs to generate something like 70-100V signals to drive the grids of output tubes which do have the input grid range to take the unattenuated signal with CC distortion and amplify it.

So yes, I agree - the preamp could do this, but IMHO it's an unusual circumstance, and easily missed or masked by overload on triode gain stages. But on the PI plates, CC distortion can be brought up into easy audibility.

I think the idea of the 'preferred value' system was that a resistor that was out of tolerance for one value fitted straight into the adjacent value. E.g. in the E6 range (+or- 20%) a 220 ohm resistor which came out 20% high is 264 ohms, which fits perfectly as a 20% low 330 ohm (which is the next value in the range). That way, in the old days, they could make a resistor, measure its value and then paint the coloured rings on afterwards. That method would imply an 'even distribution' of values within the tolerance.

Good point. I never ran into it explained that way. Makes sense. I heard "preferred value" explained as "we don't want to stock zillions of values, so figure out how to use just the preferred ones.". But target overlaps makes as good a sense as lowering stock.

[Rob's Radio-Active]

[...]Sure, CC resistors drift. that's to be expected ... but I've never seen them drift down; I've never even heard anyone report that they drift down. I've only seen them drift up, and I've never heard anyone report that they've drifted below 1/3 of their stated value. That seems to be pretty extreme. [...]

I have occasionally seen both CC and CF resistors drift downward--sometimes to less than half their original value.
cheers
Rob

[loudthud]

This is an old thread on the subject of CC distortion:

http://music-electronics-forum.com/t33206/

I posted a distortion graph of CC vs CF and they overlapped almost perfectly. Distortion was dominated by the 12AX7.

[bob p]

This is an old thread on the subject of CC distortion:

Wow, I must be getting old... so old that my memory fails me.

I'm looking at that thread from 2013, and I gave some very good reasons why I don't like using CC resistors in tube amps. Unfortunately, I had forgotten that I wrote that. If I had only been smart enough to read my own post and take my own advice from that thread, then I never would have wasted my time measuring those old resistors and starting this thread.

Now that I'm back up to speed, I can think of many good reasons not to use CC resistors, and very few reasons to use them. And those few reasons to use them are based on rather flimsy assertions.

It's funny that some of the old CC mysticism almost pulled me back in...

Maybe I should just get rid of those boxes of resistors so they'll stop tempting me to use them.

[bob p]

You don't know the half of it. Go find the video of the Tesla in France on the test drive.

Found a link. https://www.reddit.com/r/teslamotors...customer_test/

During the drive, the car complained about charging irregularities, and the salesman told the prospective customers to get out. It then burst into flames.

Talk about burned by batteries!!

Wow. I think they need to update the car's firmware. Instead of complaining about "charging irregularities" the Tesla should tell you to get out of the car and run for your life.

It's funny that the salesman knew to tell this to the customers on a test drive -- but what would have happened if the customers had bought the car and that "charging irregularity" warning was issued on their way home? In that case the car would have just complained about "charging irregularities", the customers wouldn't have known to get out, and then they could have been burned by batteries... just as if they were riding a Chinese skateboard.

I read that the threads in that link that you posted, and someone made a joke about having the car eject the battery core when it senses a fire being imminent. These stories don't make me want to go out and buy a Tesla.

[Richard]

It would be really bad if the car was parked in the garage.

[bob p]

That sort of thing happened to a friend of mine.

The 1994 BMW R1100RSL motorcycle was recalled because it could burst into flames if it was allowed to idle while standing still. The exhaust was located too close to the ABS fairing. My bike had the ABS fairing bubble from the heat damage at a stoplight. My friend's bike burst into flames while it was idling in his garage, and started the garage on fire. He lost the garage. BMW issued a recall that never fixed the problem -- they just issued plastic stickers that owners were supposed to attach to the bike, warning the operator not to run the motor while standing still. German engineering.

[Enzo]

One of my local pals was over and asked how they came up with the standard values sequence for resistors. SP I showed him the value chart. At 20%, the range of each standard value just meets the range of the next one. No point in having 20% 2.7k and 2.8k resistors. When the 2.7k might easily be 3k to start with. On to the 10% chart, and the range is half as wide per value, and there are twice as many of them, the new values added right where the 20% ranged touch. And so on, through 5%, 1%.

I was inventorying resistors here last night. Good mindless work. I am bagging my drawers. So it was a good opportunity to check them, and also toss out the little short leaded clipped off things that are decades old from my youth. I found very few 20% resistors, but I did have a lot of 10% ones hanging on. I set my meter out and found a bunch way out of tolerance, and pitched them. But in some batches I found them to be right on. I don;t know if they are AB or Ohmite or what, but I have some nice 2% resistors that are just a hair fatter than usual and have somewhat rounded ends. The color of the body is darker and has a greenish cast. Whatever they are, in any drawer i found them, they are all dead on still.

Also found a bunch of odd values at 1% and 0.1%. And some odd Sage 8250 ohm 3%.

[Dave H]

One of my local pals was over and asked how they came up with the standard values sequence for resistors. SP I showed him the value chart. At 20%, the range of each standard value just meets the range of the next one. No point in having 20% 2.7k and 2.8k resistors. When the 2.7k might easily be 3k to start with. On to the 10% chart, and the range is half as wide per value, and there are twice as many of them, the new values added right where the 20% ranged touch. And so on, through 5%, 1%.

There's a clue in the names of the preferred value series. E6 series is for 20% resistors where only 6 values per decade are required to cover the range. E12 is for 10% where 12 values per decade are required. E24 for 5% with 24 values per decade and so on.

Resistor Values

[eschertron]

It's funny that some of the old CC mysticism almost pulled me back in...
Maybe I should just get rid of those boxes of resistors so they'll stop tempting me to use them.

Mark the boxes "Hold for Pandora", and set them back on the shelf

[SoulFetish]

printable E24 series resistor labels

A few of people have mentioned doing some inventory and parts organization, so I though I'd include these labels I made a couple of years ago.
At the time I was trying to work on projects while being buried in "parts" hell. I don't know if there a more frustrating waste of time than putting the whole project of hold to spend 10+ minutes picking through a pile of components looking for a --fill in the value-- resistor.
(Well, maybe right up there would be when I can't find a tool that I literally just put down. I mean, I just had the thing in my hand... I didn't go anywhere. Where could it possibly go? Can they fly? !! )

In any case, the tool thing still happens to me from time to time, but the resistor thing does not. A couple of years ago I spent two days straight taking inventory, organizing, labeling, and (most importantly) getting rid of shit I didn't need. Part of that was making these printable labels with color codes for E24 resistors that can be used on envelopes and parts drawers. The way the values were divided up was based the inventory of resistors I had at the time, but should still work out okay for most. (The resistors around 1-1K5 happen to be on there twice because they take up two drawers.) If you want to set it up a little differently, you can edit the eps file I've attached. Let me know if I've made any errors, I did this a while ago but I can fix it quick and throw it back up.

E24 Resistor Labels.pdf

E24 Resistor Labels.eps.zip

[Enzo]

I finally finished doing mine. I found in some drawers there were a few 20% resistors, and most were within 5%, but I found some seriously drifted 5 and 10% ones. All the 1% and tighter precision ones were still dead on. So now I have a large empty drawer unit, and a couple boxes of manila envelopes. But all those old resistors with clipped off leads or twisted soldered ends are gone. Had some old one that were not even the common shapes: two watters an inch and a half long, that sort of thing.

And my god I have a million 1 meg resistors.

[bob p]

Enzo, did you ever close your shop? I seem to remember you saying that you were closing it and moving to smaller quarters. I'm wondering if you're still working or retired, and if ever parted with most of your stuff. I would think it's pretty hard to do that. I'm a hoarder at heart.

[Enzo]

I closed the shop quite a while ago, but it still sits here as I piddle away sorting through things. We are nibbling away at it. Doesn't help that I have been fighting off a low energy phase the last month or so. Sometimes I am sharp, other times I have trouble focusing. Hey, I am old and worn out.

I need to get the wife over here with her camera so I can bite the bullet and make ebay my job for a while. Not that they were here, but I finally took most of my guns to the gun shop. They sent my model 1911 off to a smith for an assessment, it needs a little work.

[J M Fahey]

......