Apple 1 Capacitors

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Clint's picture
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Apple 1 Capacitors

Has anyone got any photos of the original capacitors on the Apple 1 ?

I am specifically interested in the ceramic and the 47pf Mica.

Thanks
Clint

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Re: Apple 1 Capacitors

hello Clint,
pm sent...
sincerely speedyG

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Re: Apple 1 Capacitors

Why not here? We also need this information Smile

Gabriele

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Re: Apple 1 Capacitors

asbesto wrote:
Why not here? We also need this information Smile

Gabriele


Hello asbesto,

of course you may get that informations too. vview the related pages listed at:
http://www.harrowalsh.de/APPLEBOX/APPLE1/appleboxapple1Indexpage.htm

i just can´t repeat here entire webpages....
and i have published this link here in another thread several weeks ago....

sincerely speedyG

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Re: Apple 1 Capacitors

Sorry Smile Thank you! ^_^

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Re: Apple 1 Capacitors

hello asbesto,
don´t mind...
you probably just missed that thread...
sincerely speedyG

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Re: Apple 1 Capacitors

Clint wrote:
Has anyone got any photos of the original capacitors on the Apple 1 ?

I am specifically interested in the ceramic and the 47pf Mica.

Are you interested in the "classic" ceramic capacitors or the plastic film ones used in the NTI version? I'm planning to build a NTI version and I'm investigating the latter.

Clint's picture
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Re: Apple 1 Capacitors

I am interested in the Pre NTI version.

I would like a picture of the writing on the ceramics.

I now have a set of the Phillips electrolytic.

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Re: Apple 1 Capacitors

Clint wrote:

I would like a picture of the writing on the ceramics.

I queue up for the same info but concerning greenish NTI caps Smile

BTW, concerning big Sprague caps, anyone knows what alternative values would work in place of 2400uF and 5300uF? For voltage, any equal or higher value is fine but for capacity?

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Re: Apple 1 Capacitors

For the electrolytics caps, you can use higher capacity.

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Re: Apple 1 Capacitors

aurel6814 wrote:
For the electrolytics caps, you can use higher capacity.

this is only partially valid....
for the big electrolytic capacitors a stepup to the next higher value is O.K. ,
so you may use instead of 2500 µf => 3300 µF
and for 5300 µF you may use instead => 5600 µF or the more common 6800 µF.

But you should not use higher values....
the reason:
when powerup happens - this capacitors draw high current while loading up to default voltage and
this "spike" could kill the rectifier diodes, if you use for example double high values like
4700 µF and 10.000 µF.

The chance to use other values depends to the function the capacitor has to fullfill.

For example using higher values for the filtering capacitors ( the ceramic ones with 100nF ) or sometimes noted as
0,1 µF or other common notation 104 . Using there higher values drop efficiency for filtering the noise away from the
powerlines
.

Same is valid if the capacitor is used in frequency dependant filters
( like the ones besides the 74LS123 ( or 74123 ) and close to the crystal ....
the change of those values will have direct effect to pulse duretion ( at the 74123 )
and damage the correct timing

- or the inability to operate at the determined frequency ( at the crystal ).

so a change od values is not realy permitted in general.... it realy depends to function and location....
sincerely speedyG

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Re: Apple 1 Capacitors

I did some quick measurements and calculations and spec sheet scanning.

It takes about 30 milliseconds on my Mimeo to charge the 5300 UF cap to roughly 11 volts. Doing the calculations gives a current of roughly 10 AMPs averaged over those 30 milliseconds.

The A14F rectifiers that I am using are normally rated to 1 AMP, however they are rated to 50 amps for a one cycle surge (60HZ) and 4 amps for 8.3 msec

Because of the way the specs are made, it appears that the stock 5300 UF cap exceeds the rectifier's ratings, since the charge takes more than 1 60 HZ cycle (16 milliseconds). On the other hand, the 50 AMP rating would seem to indicate that there might be some margin left in the design, since we are only charging at 10 AMPs, not the full 50.

This is an interesting exercise and one I would take seriously, if I were designing new equipment, but something that probably isn't going to cause you trouble, unless you far exceed the original values.

regards,
Mike W.

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Re: Apple 1 Capacitors

This was my primary concern, but given that voltages involved are relatively low and in the NTI version 8 x A14F seem to be used, do you think it could be safe to even double the caps value?
The A14F has peak surge current rated at tens of Amperes.

Edit:
ops... didn't note that Mike W. already provided an answer Smile

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Re: Apple 1 Capacitors

Hello Mike,

thanks for adding the results from your research......
the thing i mention about is rather more not the fact of one single "loading cycle"....
this happens each time the computer is switched on ! So we are talking about a repeating event !
this surely won´t cause damage with the first several "power ups"... but what happens in fact is
that the limits are repeatingly exceeded if too large values of the caps are inserted and each single
exceeding causes "micro damage" (*)within the diode and such small damages don´t heal but sum up by time ...
... and that shortens life of the device rapidly....
a diode that might last for 5 to 10 years in "normal use" will fail sooner after probably 1 or 2 years
if the values are exceeded that far.....
why do the consumers always believe that electronic devices have eternal lifetime ? That´s not true....
- using wrong values was for years a common trick to shorten down "time of life" for such devices
and you can do that by exceeding electrical limits or for capacitors for example also by exceeding
surrounding temperature.... if you want reliable electronics you should keep within electrical limits.....
..... everybody doubting about this should "google" the topic about obsolescence and learn careful about that topic...
of course with the stuff at google you won´t be able to get details like explained here by me, but it at least explains about what i´m talking about... the rest can be researched by scientific examinations on the physics of electronical devices within universities....

(*) small changes in the siliciumoxid transient areas

sincerely speedyG

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Re: Apple 1 Capacitors

As you say a higher voltage will work fine, and you can use a larger capacitance value, but not too large.

Its a common misconception that throwing the largest value capacitor will make for a better power supply, this works in theory, but in practice the larger the Cap the more the power diodes have to supply higher current to charge the caps. Peak current in the power diodes can double or triple as the capacitor size climbs, this is OK if you take this into account in your design, by replacing both the diodes and the transformers.

I remember as a radio trades apprentice thinking just this. Build a power supply, rated at 5V, 3A, use 5A diodes to be safe (as this turns out this was 1977 and used an LM323 regulator). Pick a transformer with 8V with a 3A secondary. Throw in the biggest electrolytic I could find and within an hour the transformer was near critical mass, with a surface temperature too hot to touch. One of the engineers working with me chuckled and reduced the main filter electrolytic to a much smaller value and the problem was solved, 4,700uF from memory.

The resultant voltage out waveform doesn't need to be super smooth, as long as the lowest point in the waveform is around 2V above the output voltage of the regulator the regulator will provide a nice smooth 5V DC out.

I wouldn't go more than 2X the capacitance in the original WOZ power supply circuit.

Cheers, Martin...

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