Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 21, 2017, 05:55:14 am
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This morning I was to the electronic components shop (the only one in my town) to purchase some components for my AA764 project
I asked for 25uF 100V capacitors to be used as cathode bypass capacitors but they were not available, they had only 22uF and I got it
At home I was looking for the 25uF capacitor at the RS online shop and they had some (from 2€ each till 5.40€ each), but
the spec I've read say that they have (-10% +50%) or (-10% +75%) of tollerance (depending on model)
I know that e-caps tollerance % is large and reading that they can arrive till +75% & -10% made me think I can use the 22uF that I've find instead
of those 25uF indicated on the schematic
Which is your opinion about ?
Thanks
Franco
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I think as long as the 22uf has adequate voltage rating for where you are using it that you will never be able to hear any difference at all between 25uf and 22uf.
At least, I have never been able to hear any difference. I wouldn't hesitate to use it.
With respect, Tubenit
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Thanks Tubenit
Franco
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How much uFd do you *need*?
In many cathode-cap applications, anything 10-15u on up is all the same. But in the old days a "10u" cap could be 5u and wind up a little shy in the bottom octave. Old-US values went roughly 2:1, though the next step up might be 25u, so that was the number on the old schematic. Today we find tighter tolerances, many more available values, 1.4:1 steps, and this would be a 22u. Though if you are unsure, more is often better, so you could get 27u.
Again with my dog-porch. I calculate that I need good-wood beams 1.9" deep. (Small dogs.) I know lumber varies in strength so I might specify 2.2" any-wood. I go to the lumber yard and discover that they only go down to 'by 3', which is today really 2.5" +/-0.05". $3. I go over to the cabinet maker and he will cut me some real-good wood to my exact 1.9" size. $20. I go back and get the mass-produced "too big" sticks. The dogs don't care if it is "too strong".
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Haha! Nice analogy PRR. I like that!
I've swapped 22uf's into 25uf spots on numerous things and heard zero difference. I'm building a vibro champ right now, and one layout calls for 10uf on a cathode, and the other layout calls for a 25uf.. I have both, and I'm going to run some experiments there, and I'll let you know what I think personally.
That being said, the other three 25uf's are all getting 22uf Suntans I got from TubeDepot a while back :icon_biggrin:
-Brett
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> one layout calls for 10uf on a cathode, and the other layout calls for a 25uf.
Marshall used 0.68uFd. That is different.
In the usual Fendery stage, anything over 5uFd is probably all the same, especially for guitar. But 25-22u hardly costs more.
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OK :thumbsup:
Franco