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I have a Herald (made in Japan) tube phono preamp I want to restore and use. It had a bit of hum so I am replacing the big PS caps, but there are two others I want to replace. They look like paper caps with a value of (it says) 0.0004 written on them. I want to replace with a more modern cap (I am pretty sure these carry an audio signal)but what values would work? I have some .02uf mylars on hand.In the picture they are the two rectangular reddish-brown caps, upper middle. They have a 1kV rating and appear to have polarity - silver dot?
Not sure if this number, molded into the covering of the cap, is in picofarads.
Any advice welcome.
Follow Ups:
The caps in question are silver mica and very rarely fail. If you want to replace them, they are 400 pico farad. I would however replace the other caps as they are paper in oil and are guaranteed to be bad. Good luck with your project, Harry
These things were marketted under quite a few different brand names. Those caps that you mention are all micro farad (uF) values. I think Sprague 716P's wopuld work just fine as replacements. These preamps are not very high quality, so you may never be happy with the sound. Good luck,
I suspect you are right about the quality. I thought if I tweaked them a little, they would sound better. No big investment.
The brown caps are pico farad caps. I would leave them be. The other oil caps are a more likely upgrade target as described in my post above.
This might help.Best,
CAC
Thank you for the link - that is useful info. These caps aren't like that - no color dots, just one silver dot, and they read 0.0004 uf. A small value. Maybe I'll just leave them in.
The guys over a "tube/DIY" could probably give you the answer you seek.
Thanks. Did that, along with corrections.Pete
Vintage Voltage Expo - Denver
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