The AM Forum

Hi,
Working on an old tube tester, bringing it up to better working condition, so I can calibrate it.
It went out of cal in 1961!

Found two of these old “6 dot” caps in it.
The  Hickok 539B factory parts list says the red C5 is a 470pf, 500volt, and Google found me the decoding rules for the old red cap that agree.

However, the tan cap is a Cornell-Dubilier type 1, and Google did not come up with anything that matched it.
it is not in the 539B parts list, but there is a 2700pf ,1kv Mica in the 539C parts list.

If it is paper, is there any reason I can’t replace it with a Mica?
I pulled it out  and put the cap on the tester, it reads 2800pf

So should I just give up trying to find the secret decoder ring for the tan cap, and just replace it with a 2700pf , 1kv mica?
73
Frank
KJ4OLL

Do the dots look somewhat like arrows? I think you could find an old handbook with the code.

I used to have a 'cheat sheet' for those little guys...

I scanned a page to PDF from the 1945 Allied Radio Data Handbook that explains the color codes for mica capacitors.  Hope this helps you sort it out.  GL.

Thanks Very Much! That chart decodes the tan cap!!!!!

You're Welcome.  Glad it was helpful.

2700pfd 10% 500v 

That's what I calculated. But I didn't want to take all the fun out of the troubleshooting.  I suspect the value is not extremely critical for that application.

By the way, the conversion factor from uuf (micromicrofarad) to pf (picofarad) is the same formula that we use to convert cps to Hz.  I was always comfortable with uf and uuf,  pf is OK,  but I find nf (nanofarad) confusing.  Just getting old, I guess. 

I agree about the nf being confusing.
The HP 4262A LCR meter displays in nf, I had to make up a conversion chart, taped to the front panel, nf---mmf---pf

2700pfd or 2700uufd equals 2.7nfd

http://www.radiodaze.com/vintage-component-color-code/

Radio Daze in NY has a nice color reference chart for resistors, caps, etc.

Just Radios also has a pf / nf conversion chart on their web site.

I did not mean to imply that the conversion from pf to nf was difficult; so for me a conversion chart is unnecessary.  But when I started working with these things, cps, uf, and uuf were the common terms; pf makes sense instead of uuf, but nf is confusing only because I am unaccustomed to using that notation.  NF makes my head Hertz.

I would normally think of 2700 uuf or pf as .0027 uf, not 2.7 nf.  As time goes on I will probably be more comfortable with it, but I really don't see the need for the nf notation in capacitors.  Maybe because they are physically smaller than in the past, nf makes labeling them more practical.  But when working on a circuit I always have to mentally convert from nf to uf or pf to understand what is going on. 

Mental block of the aged, or the onset of senility, one or the other????