Artificially aging an amp by using off-value components

[VacuumVoodoo]

Aleks, I know it sounds wrong, but I have dried out over a hundred old orange drops and chocodrops that had spent 30-40 years in non-A/C storage in Houston, a very humid climate, and that gets them back in spec about 90% of the time. It takes about 72 hours at 225 deg F in a convection oven to do it.

I measured them before and after drying them out and there is no doubt that the values do come down quite dramatically in most cases.

If it's not humidity what else can it be?

Well, I must honestly say I don't know. I never try to resurrect dead components or that have drifted beyond spec limits. They all go to the nearest recycling plant.
I might attempt to bake and re-impregnate a leaky cardboard from a water damaged old Fender, but that's really as far as I will go. A new eyelet board is cheaper and faster to install in most cases.
Most film caps are supposed to be hermetically sealed, if they sucked up some humidity it means the sealing has become compromised. I suspect that even if You bake them dry as bone in the desert, they'll suck up humidity again sooner or later.
We'll see what some capacitor data mining will produce.

[rdjones]

Aren't many caps -20%, +50% tolerance to begin with ?
So they could be off by quite a bit and still be "in tolerance".

rd

[VacuumVoodoo]

Aren't many caps -20%, +50% tolerance to begin with ?
So they could be off by quite a bit and still be "in tolerance".

rd

Electrolytics, yes. That's the most relaxed specs, you can get +-10% electrolytics for a price.
Film caps can be had as tightly spec'd as less than 1%.

[martin manning]

Film caps can be had as tightly spec'd as less than 1%.

But more often they are 20%, which in terms of the shift in the frequency of the -3dB point in an RC filter nw is about a flat third, musically speaking.

[Reeltarded]

Flat third? That sounds like a minor difference.

[martin manning]

I nominate Miles for this week's Rim-Shot award.

[Reeltarded]

If nominated I will not run and if elected I will not serve.. but I will attend the big dinner.

[VacuumVoodoo]

Film caps can be had as tightly spec'd as less than 1%.

But more often they are 20%, which in terms of the shift in the frequency of the -3dB point in an RC filter nw is about a flat third, musically speaking.

Martin, are you serious? +-20% caps in frequency selective and voicing circuits?
Coupling caps in LF high pass - max 10%
Caps in Bass tone control: max 5%
Caps in mid & treble tone controls and other voicing filters max 2.5% but preferably 1%
All resistors 1%
Potentiometers selected to 5% or measured up and accompanying components adjusted accordingly.
Otherwise I wouldn't be able to build two amps that sound and feel almost
identical.

[martin manning]

I'm thinking old parts in vintage amps (like the ones DR was trying to "restore") here. They were no better than 20% except for things like bias resistors, which were 5%.

[VacuumVoodoo]

Aha, that's a different pair of galoshes.

[David Root]

Sorry I should have mentioned I was dealing with old Sprague 6PS and 220/225 orange drops, and CDE & El Menco/Arco chocodrops, all of which are +/- 10% tolerance, not 20%. Mostly 600V, with some 400V, mostly chocodrops.

Naturally I try to use closest to spec, when I get to the marginal ones, back in the oven most likely.

[martin manning]

After looking at a bunch of schematics and pictures of vintage amps it appears that 10% was pretty standard for tolerances of both resistors and caps, with 5% for resistors in a few locations (PI plate loads and bias circuits).

[Structo]

Not sure if this was mentioned but, say you do use off spec parts.

Although modern components don't drift in value anything like vintage parts did, what happens when your off value parts do drift?

I have heard of many stories about guys that bring their beloved Tweed amp into a tech for a cap job or other work only to complain how it sounds after the work is done.
Of course we have seen the "cap jobs" that some ignorant techs do that entail replacing all the film caps with orange drops.......

But I suppose if you took a very good sounding vintage amp and measured each component and built a clone with those values, it might sound good but............ it might not.

Also worth mentioning is the fish paper circuit boards that Fender used back in the day that would become slightly conductive with age.
How does that fit in the play book?

[Wallbanger]

Wow, if a component I used changed value by a significant amount by baking it dry I certainly wouldn't use it. There's something WRONG with it, it's going to condition to normal (relative) humidity levels and change values, or fail from corrosion. I'd be most worried about shelf life due to moisture exposure. Unless I was selling to people that listen by looking at component values/types/colors etc. instead of closing their eyes and playing my amp. I don't. If someone asks me what BRAND of caps I use, I immediately know they are FOS and are a plonker. Thats fine and I respect them and their wallet. I answer them respectfully and tell them what makes them feel good. The TRUTH is, the hand lotion they used before they picked up the guitar matters more.

Psst, new caps work better! You should test those old od's on a piece of equipment that can supply the rated voltage, i.e. not an esr meter.