Hi vince666,
I'm in the process of attempting to transition a bunch of equipment from a couple of decades of cold storage to daily use as my main system, so I was also reading what Grapplesaw & others were saying about forming/reforming capacitors.
This evening I read your restoration thread with interest, especially how your equipment sounded so disappointing on the
first try, but so much better the 2nd time around? Believe it or not, I found a couple of technical white papers about the electro-chemistry behind the aluminum electrolytic capacitors that discuss the exact scenario that you had described earlier.
Check out this paragraph I took from a Cornell-Dubilier paper:
View attachment 62172
Q: Did you catch the "reluctance to charge the 1st time" comment, followed by the excess leakage current? Obviously, a circuit where the voltages aren't where they are supposed to be due to the above will not operate/sound right -- especially if the capacitors are being used to couple the music signal between stages. NOTE: The 'smaller' the coupling capacitor, the more of the bass frequencies are blocked?
(Refer to Cornell-Dubiliar .pdf file attached to the end of this post for more info on cap forming/reforming.)
In a different paper there were a couple of photos associated with how the surface of the aluminum is etched during forming in order to provide up to 200x more surface area. Of course, more surface area = more capacitance. Check out these micro-photographs:
View attachment 62173
(Refer to EPCOS .pdf file attached to the end of this post for much more info...)
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Guess what? If you tunnel deep enough to where all the people that actually design/develop/manufacture electrolytic capacitors hang out, it's neat to see that some of the weird/voodoo
subjective behavior that
we observe our old & complex audio equipment do...can actually be explained using their
objective scientific papers. (!)
Good for you to state in public exactly what you heard the first time...a little time passes...and then the 2nd time you listened it seemed to have magically healed itself? In other forums I've seen people being ridiculed for what they heard & reported...but in the back of my mind I was thinking that anyone sharp enough (patient enough/disciplined enough) to completely tear down that Telefunken deck and successfully put it all back together...if they said it sounded bad on the 1st try, but seemingly fixed itself on the 2nd try? I gotta believe them! :0)
You know, we tend to lose sight of the fact that we aren't trying to restore old, simple cast iron skillets. (Although there are people that do just that.)
A lot of the equipment that we are interested in restoring were literally 'state of the art' when they were made. And due to the limitations of that generation's test equipment, designer's knowledge, lack of powerful computer simulation tools, and even competitive pressure to get new stuff out into the marketplace asap, some of these very technical machines were only partially-baked when released.
Such is the nature of the beast. Given the above, some of our favorite toys were finicky/hard to fix when they were only 4 years old...much less 4
decades old. (!) Imagine if you & I were putting together something as complicated as that Telefunken today -- and somebody asked us how is it going to behave in the year 2065? We would laugh out loud at how absurd the question was. :0)
The point I'm trying to make is that for the love of music we are trying to revive really complicated equipment decades after (most of) the original designers figured that these boxes would be in the landfill instead of the living room.
What a hobby. I just wanted to listen to some of my favorite tunes that are no longer being played on the radio...one thing leads to another...and now I find myself studying electrolytic capacitors at a level I would have never, ever predicted. Go figure. :0)
Cheers --
3D
PS -- Congrats on seeing that huge project through to completion. Man, whoever spec'd that huge motor to drive a cassette deck must have really had a thing for low wow & flutter - impressive!
