Mica Capacitor (Domino) ID question

[Wharfcreek]

Working on an old Baldwin amp, and there's a domino cap in the input stage that I'm not quite sure about. I looked it up based on an old post that Tom Bavis had made whereby he posted a link to a chart that Allied Radio had formulated some years back. Here's the problem; I'm not sure if I'm reading things properly, but as I see it, either the chart is off, or my Capacitor tester is wrong....or I'm just misinterpreting things.

According to the chart, upper left corner in a 6-color cap, if 'white', means it's a mica cap. Mine is white. My next color (position A) is 'yellow', and per chart that is a '4'. Next color (upper right or position B) is Red, which chart calls a '2'. Then things get 'sketchy'. The lower row seems to read from right to left, and 'skips' position 'C'. Moving to position 'D' (lower right) it appears that this 'multiplier' in this case is 'black' or 1. Given this to be a uuf chart, this reading should be = to pico farads. So, putting my capacitor tester into it's proper range, the cap reads as a .462nf. (my meter reads this cap in the 2nf range). So, that would be equal to a 460pf cap. Yet the chart seems to indicate that it should be a 42uuf (pf) cap. Hence my question. Should not the chart show the multiplier as being a 10 instead of a 1...which would make the 42uuf X 1(multiplier) actually be a brown....or maybe my brown just faded to black after all these years...?

Pic to come shortly..... Thanks, WC

 

[wa2ise]

I see a purple dot on the upper right, and that would mean a "7", and thus, with the other dots, 470pF.

The multiplier dot looks brown to me. which puts it in 100-999 range.

 

[gadget73]

I'm with him. I see 470pf as well. That would be a sensible value too, given what you measure it at.

 

[Wharfcreek]

So basically what I saw as 'red' is really 'purple'...and what I saw as 'black' is really 'brown'. Well........like I said, maybe I was just reading it incorrectly. The Cap Tester did show it as a 462pf cap......so if it's value should have been 470 per the color code, then I guess it's close enough for practical purposes.

BTW, I finished the amp about 30 minutes ago.....and I'll post a few pics tomorrow.

Thanks guys! Tom D.

 

[gadget73]

I suppose the question ought to be, what does the schematic ask for? Its possible that it *should* be 47 and has gone flukey. Those mica caps are usually fairly stable, but they can and do go bad sometimes. I don't have anything that will read them myself, so I usually have to infer if they are right based on how stuff acts. Mostly I deal with little values in tuners, so if the tuner is way off, it stands to reason that its because the cap is off.

 

[Wharfcreek]

Hey Thain,

A good question as to 'what does the schematic call for?', but unfortunately the schematic actually omits a value on this particular component. I should mention that the schematic was actually drawn up by Paul (Secret4mula on AK) and he did so by dissecting a working amp. However, I'm guessing that when he ran into this Mica cap, he had no way to measure it, nor did he take the time to research it's value. So, his schematic shows it, but no value assigned to it...which is why I was asking about it in the first place. Funny, but the 'purple' still looks 'red' to me, as the the brown that I think looks black. But, I don't look at these caps often enough to actually become 'tuned in' to the color scheme. But, the amp is done and working, so I guess all is well. Thanks for the help ......... Tom D.

 

[gslikker]

If the multiplier is 1 this means "one zero", so equivalent for number is 471. This means 470 pF not 47 .

 

[Wharfcreek]

That clears everything up! Now it all makes sense, and it's consistent with my measurements. I was kinda hoping that would be the answer........so, I REALLY appreciate the explanation. Thanks gs! Tom D.