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Old 11th August 2011, 11:58 PM   #1
PJN is offline PJN  United States
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Default Help with ID of film cap

Hi All,

I'm hoping that someone help me understand the designation of a film cap. I'm thinking of upgrading some film caps in a preamp. They are rated for 250v and have the designation 105J printed on them. Does anyone know what 105J means in terms of uF ?

Thanks,

PJN
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Old 12th August 2011, 12:05 AM   #2
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J means something else. As I recall, (a bit rusty nowadays) the 105 should equal 1uF. 104=0.1uF 103=0.01uF 102=0.001uF 101=0.0001uF. Have seen 106 used for 10uF. Doc (either that or its a date code for fifth week of 2001)
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Old 12th August 2011, 07:29 AM   #3
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I don't think there's a formal standard, but some manufacturers code the tolerance with a letter like that. I think "J" is a 5% part. The other possibility is the voltage rating - but if it's already marked "250V", I'd wager the "J" is the tolerance.

Dale
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Old 12th August 2011, 02:14 PM   #4
PJN is offline PJN  United States
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Thanks guys
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Old 12th August 2011, 02:34 PM   #5
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Before randomly "upgrading" caps, you need to know where they are in the circuit. Otherwise you're apt to cause more problems than any improvement you might get. Can you post a schematic? And a picture? Next, it's uncommon for film caps to be marked with the "105" designation for value. Not unheard of, but not common except for small radials. that method is more often used with ceramic caps and silver-micas. Ceramics would be used for bypass and film might be a better choice, or not. Silver-mica can be used successfully in RIAA networks and filters, sounds good, but polypropylene is likely a better choice.
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Old 13th August 2011, 11:53 AM   #6
PJN is offline PJN  United States
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Hi Conrad,

The caps in question are in a cheap Chinese tube preamp that I bought. I've attached a pic. The caps in question are the little brown ones between the yellow 0.47 uF caps. Unfortunately I haven't been able to get a schematic, but from looking at the traces on the board I think that they might be coupling caps. The electros are power supply caps. I was thinking of replacing the 0.47 uF yellow caps with some film and foil caps, and the brown 1 uF caps with a decent quality polypropylene metallized film cap. And leaving the PS caps alone.

PJN
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Old 13th August 2011, 01:01 PM   #7
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Wow, there's barely enough parts on that board to call it a "circuit"! Other than the PS caps, my guess is everything else is polyester (Mylar) and would benefit from being changed to polypropylene. The trouble is that you just don't know what they are now- they might already be polypropylene. The new ones may be larger, especially because you need a decent voltage rating and also if you go with foil types. I'd upgrade the resistors as well, but that's just me. Be forewarned that these "upgrades" could very well give you a harsher less desirable sound. IMO, and it's been a long while since I did anything with tubes, tube amps can sometimes be more sensitive to component choice than solid state.
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Old 16th August 2011, 12:12 AM   #8
glennb is offline glennb  Australia
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Quote:
Originally Posted by PJN View Post
Hi All,

I'm hoping that someone help me understand the designation of a film cap. I'm thinking of upgrading some film caps in a preamp. They are rated for 250v and have the designation 105J printed on them. Does anyone know what 105J means in terms of uF ?

Thanks, PJN
3 digits followed by a letter is a very common designation on leaded film caps.

See Capacitor Codes - Transwiki .

An easy way to remember codes like 105 is write down 10 followed by 5 zeroes. This is the value in pico Farads. eg. 1,000,000 pF = 1,000 nF = 1 uF.

eg. 333 is 33000 pF = 33 nF, 472 is 4700pF, 121 is 120 pF

The letter is the tolerance on the value, the most common are J=5%, K=10%, M=20%
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