5e3 capacitor values

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phsyconoodler
Junior tube assistant
Posts: 3
(3/2/04 4:11 am)
 5e3 capacitor values
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 Can anyone tell me why some 5e3 builds use different filter cap values? My build uses 30x 20x20. I've seen lots of variations.  
Thanks, phsyconoodler
 
jc
I only work on Fender's
Posts: 680
(3/2/04 6:52 am)
 Re: 5e3 capacitor values
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 The higher value filters the AC ripple better so you get less hum and they also provide a better bass response. Fender used the smaller values probably because of cost more than anything.
 
Voxbox
Junior tube assistant
Posts: 64
(3/3/04 6:37 am)
 Re: 5e3 capacitor values
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 Is there a max that can be used, and what is the limiting factor?
 
GroundhogKen
Forum Moderator
Posts: 2305
(3/3/04 9:39 am)
 Re: 5e3 capacitor values
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 A 5y3 really doesn't like to be loaded with more than 33uF. So the first stage (B+) filter shouldn't be any bigger than that.

Ken
 
Voxbox
Junior tube assistant
Posts: 65
(3/4/04 8:30 am)
 Re: 5e3 capacitor values
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 Thanks Ken,
How do you work out the max capacitance from the tube data?
Cheers
 
Craigzbrand
Junior tube assistant
Posts: 81
(3/4/04 7:28 pm)
 Re: 5e3 capacitor values
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 I just built an amp using a 5Y3, and I'm a little embarassed to say that I didn't think out the max input cap value. I used a 47uF for that first cap. I think I should pick up a 33 as Ken suggests, but I am so happy with how this thing sounds, I'm afraid it may change something. Ken, any feedback here on what I can expect by making this change would be GREATLY welcomed!

I guess when you first switch the amp out of standby, there's a pulse of current that can exceed the amount the rect tube plates can withstand, but only for that short interval as the cap charges. After this occurs over and over, the life of the tube is shortened. Have I got that right? Or is the rect. under constant stress during normal operation?

The tube data sheets will give examples of cap input supplies and choke inputs at given voltages, and sometimes there'll be a little footnote given for the circuit designer that tells them "max cap input value can exceed "X" mfd if plate supply impedance is increased to compensate to prevent going over max plate current," something like that. How do I do that, anyone?

The obvious answer is probably "Go get yourself a 33mfd, install it, and forget it!" but for me, the learning continues - Thanks in advance - Craig
 
Jonas Gemini
Hey get your own solder
Posts: 305
(3/4/04 9:49 pm)
 Re: 5e3 capacitor values
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 Craig and everyone else

did you notice a decrease in hum as you increased the cap value?

I am currently using 16uf - choke - 16uf and don't get much hum, but can hear white noise when the amp is cranked.

Will increasing the first cap reduce hum? because I have very little hum when the amp is cranked/\ ?

Jonas


 
Craigzbrand
Junior tube assistant
Posts: 82
(3/5/04 10:59 am)
 Re: 5e3 capacitor values
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 Hi Jonas - no, all I notice is the bass isn't flappy when cranked, seems tighter than my 5E3. Of course, other than both being cathode bias 6V6 amps, they're a bit different, so that makes it really hard to compare. I'll post back later with the results of using a 33mfd. Hopefully, it won't change the response, but it makes more sense to alleviate the stress on the 5Y3. Craig
 
phsyconoodler
Junior tube assistant
Posts: 5
(3/7/04 9:45 pm)
  Re: 5e3 capacitor values
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 Thanks for the info guys,I feel 'informed' now.
 
Craigzbrand
Junior tube assistant
Posts: 83
(3/10/04 2:08 pm)
  Re: 5e3 capacitor values
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 It doesn't play different with the 33mfd input filter that I can tell. Glad I ran across this thread and Ken's advice re 5Y3 max filter value. Thanks! Craig
 
 
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