Mike Knudsen wrote:

Nope, you make sense. Maybe not so much demand in the Ham BA world, but over
on radio+phono you'll find purists who want caps to stuff. The problem is,
they already have the original old caps in the radio they're restoring, so they
don't need yours.

Not always...thats why I need more. Often times the original caps have
already been hacked out or are in too terrible a condition for restuffing.
I try to keep some made up ahead of time and where a set like a Zenith
or Philco uses brand specific ones I like to replace with the same. I
considered stuff-n-sell but it really is a time consuming task. I'd
feel stupid trying to sell them at what they are worth dollar-wise in
time...and of course anyone can do their own for free if they really care!

But -- some enterprising retiree may want to stockpile pre-stuffed restored
caps and sell them to other restorers, ready for insertion in the radio. If
so, he'd want yours for starters to build up inventory. Ultimately, he'd take
the old ones in exchange, but meanwhile he needs extras.

Hopefully he'd pay enough to cover the postage :-) --Mike K.

I beg for these things! And of course always pay postage!

-Bill

The capacitance and voltage rating of an electrolytic capacitor is
set by the thickness of an aluminum oxide layer deposited on the
metal foil "plates" of the capacitor. Of course, the bulk amount of
square inches of aluminum plate material also determines the range
of capacitance that is possible with varying thicknesses of oxide.

The electrolyte serves the purpose of making an intimate electrical
connection to the plate. The problem is the electrolyte shows some
tendancy to dissolve the oxide layer. When this happens, the
capacitor's value increases, and its safe voltage rating decreases.
This is why a long disused electrolytic capacitor tends to blow up
when it is abruptly put back into service.

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

The tolerance has nothing to do with manufacturing capabilities, or
price, and everything to do with the highly variable nature of the
oxide layer.

-Chuck, WA3UQV




Mike Knudsen wrote:
In article , "Frank
Dresser" writes:


Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!


This makes very good sense.
I suspect that back in the old days, manufacturers would throw in up to 100%
extra foil plates area just to make sure they at least met the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why toss in extra
material. In fact, shaving it on the low side is just what the front-office
bean coutners probably tell them to do nowadays! --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

The capacitance and voltage rating of an electrolytic capacitor is
set by the thickness of an aluminum oxide layer deposited on the
metal foil "plates" of the capacitor. Of course, the bulk amount of
square inches of aluminum plate material also determines the range
of capacitance that is possible with varying thicknesses of oxide.

The electrolyte serves the purpose of making an intimate electrical
connection to the plate. The problem is the electrolyte shows some
tendancy to dissolve the oxide layer. When this happens, the
capacitor's value increases, and its safe voltage rating decreases.
This is why a long disused electrolytic capacitor tends to blow up
when it is abruptly put back into service.

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

The tolerance has nothing to do with manufacturing capabilities, or
price, and everything to do with the highly variable nature of the
oxide layer.

-Chuck, WA3UQV




Mike Knudsen wrote:
In article , "Frank
Dresser" writes:


Just as speculation, let's say cap manufacturers have learned to make
electrolytic capacitors with good precision at little extra cost. And let's
imagine that setting the target capacitance to 5% - 10% low reduces the cost
of the "active ingredients" by 5% -10%. Well, that would be a nice reward
for knowing how to do the job!


This makes very good sense.
I suspect that back in the old days, manufacturers would throw in up to 100%
extra foil plates area just to make sure they at least met the rated
capacitance. So you would get caps well over the ratings.

But yes, once they got the process down really tight, why toss in extra
material. In fact, shaving it on the low side is just what the front-office
bean coutners probably tell them to do nowadays! --Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

Chuck Harris wrote:

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

-Bill

Chuck Harris wrote:

Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.

Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

-Bill

"Chuck Harris" wrote in message
...
[snip]

The tolerance has nothing to do with manufacturing
capabilities, or
price, and everything to do with the highly variable
nature of the
oxide layer.

-Chuck, WA3UQV


OK, I'll grab some of those old Ducatis and check 'em. I'm
sure they haven't seen a polorizing voltage in at least 25
years, because that's when I bought them as surplus.

Then I'll run 'em up to their rated voltage for 24 hours and
recheck.

I'll see how much extra voltage they take and hold them at
that voltage for another 24 hours.

Just for curiosity, I'll also check the ESR at each step
with my Dick Smith meter.

I know none of this is lab quality procedure, but if there's
any gross changes, I think I'll catch 'em.

Frank Dresser

"Chuck Harris" wrote in message
...
[snip]

The tolerance has nothing to do with manufacturing
capabilities, or
price, and everything to do with the highly variable
nature of the
oxide layer.

-Chuck, WA3UQV


OK, I'll grab some of those old Ducatis and check 'em. I'm
sure they haven't seen a polorizing voltage in at least 25
years, because that's when I bought them as surplus.

Then I'll run 'em up to their rated voltage for 24 hours and
recheck.

I'll see how much extra voltage they take and hold them at
that voltage for another 24 hours.

Just for curiosity, I'll also check the ESR at each step
with my Dick Smith meter.

I know none of this is lab quality procedure, but if there's
any gross changes, I think I'll catch 'em.

Frank Dresser

--exray-- wrote:
Chuck Harris wrote:


Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.


Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

It is all about the electrolyte. The older electrolytes tended to eat
the oxide layer pretty quickly. The manufacturers rated them for a
1 to 2 year shelf life... longer if they were in continuous use.

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

-Chuck

-Bill

--exray-- wrote:
Chuck Harris wrote:


Electrolytic capacitors are self adjusting for working voltage (to
some degree). If they are operated for a long time at 50% of their
rating, the oxide reduces in thickness, and they become higher
capacitance, and lower working voltage. If you try to increase their
operating voltage, they will draw too much current. They will either
adapt to the new higher voltage, or they will blow up from the heat.


Thats very much true with older caps up to about 1970. But later model
caps don't exhibit this 'memory'.

It is all about the electrolyte. The older electrolytes tended to eat
the oxide layer pretty quickly. The manufacturers rated them for a
1 to 2 year shelf life... longer if they were in continuous use.

There have been alot of improvements in the electrolytes, and now the
caps last virtually forever. But the oxide thickness still determines
the tolerance, and as such it still changes with temperature, age and
voltage. Just not as much as it used to.

-Chuck

-Bill

Frank Dresser wrote:

OK, I'll grab some of those old Ducatis and check 'em. I'm
sure they haven't seen a polorizing voltage in at least 25
years, because that's when I bought them as surplus.

Then I'll run 'em up to their rated voltage for 24 hours and
recheck.

I'll see how much extra voltage they take and hold them at
that voltage for another 24 hours.

Just for curiosity, I'll also check the ESR at each step
with my Dick Smith meter.

I know none of this is lab quality procedure, but if there's
any gross changes, I think I'll catch 'em.

Frank Dresser



That would be fine if you are looking to get doused with electrolyte.
A better test would be to measure the capacitance as they sit.
Then reform them with a 1.5K resistor in series with the supply.
Then retake the measurements.

If the cap isn't drawing current during the reform, it means the
maker got the electrolyte formulation right, you probably won't see
much change in measured characteristics. If the cap is drawing
heavy current during the reform, you should see greater differences
in the reformed cap vs the "NOS" cap. ESR should go down, capacitance
should go down, and so should leakage current.

-Chuck, WA3UQV