Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jordan86 on April 17, 2020, 06:25:47 pm
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Newbie question...
DO BYPASS CAPS NEED TO BE POLARIZED? A lot of the kits appear to use polarized. My gut says they don't, (like a treble bleed circuit in a guitar) but again, I'm a newbie.
I am ordering my first amp kit here soon. Mojotone Princeton Kit. It seems to use real solid parts, so I'll do it mostly stock with a few tweaks. Probably with a 12" baffle and the Allen TO20. Maybe Paul C mod. I've also been reading about dropping the value of most of the cathode bypass caps in the Princeton to tighten up the lows. I'm somewhat of a noob, but I've been watching a lot of Uncle Doug's videos. The smaller bypass cap value seems to dial back muddiness and the gain just a touch?
4.7uf seems to be a good value (opposed to stock 25uf) but I'm having trouble finding those in like the 50-150v range that are electrolytic, polarized, and have axial leads. Hence my question.
Other Q's...
1) Is there a particular brand you guys like for cathode bypass?
2) Do they have a big effect on tone?
3) Who's your preferred online retailer?
4) I'd gladly welcome any input on that values of 4.7uf vs like a 2uf or 8uf.
THANKS IN ADVANCE!
Edit: Upon further review, it looks mr hoffman himself sells 8uf/150v Spragues and 4.7uf/100v Nichicon. Will those work alright? My understanding is the bypass caps see less than 25v.
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Right here in Doug's parts, scroll down
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any brand flavor is fine, maybe not 1000 for a $, otherwise I use anything.
Ecap is not necessary, just preferred, a 4.7uF non-polarized might get salty.
have 3 ea common 1uF - 25uF, most "V1" tubes have < 3vdc at cathode, most tubes prior to PI, <10vdc, so double and round up to common.
then gator clip, play, next........
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> DO BYPASS CAPS NEED TO BE POLARIZED?
NO.
But useful values for audio range 1uFd on up. In this range, electrolytic caps are by far the cheapest type, and work fine for decades.
Non-polar electrolytic costs a little more for no benefit.
Paper and plastic film caps will work fine, are not polar, will last several lifetimes, but a 20uFd film is BIG and COSTLY (even at low voltage).
20uFd 15V e-caps (polar) are a dime apiece in mass production and work fine. (Yes, if you need less than a full crate the price is higher, for picker-labor and because the store never sells-out a broken case.)