Searching for lower cost filtering for 2203

[hesamadman]

Im looking for a possibly cheaper alternative to the 50/50 cap cans for a 100watt 2203 using 6L6's. I was hoping to build a small board on the side using smaller/cheaper single 50uf caps. I can only find 47u/450v. Any suggestions?

[John]

Stack 2 100uf/350volt caps? That'll give you 50uf/700 volt per stack. Not sure it'll be cheaper in the long run though. Almost certainly will take up more space.

[hesamadman]

I was going to say 100u. I always forgot how voltage rating works with caps in series and parallel. Series = add voltage? Is it the same with parallel?

[hesamadman]

It looks like I can get Cornell Dubilier Aluminum Electrolytic Capacitors - Snap In 100uF 400V 20% for about $2.51. These should fit onboard. Much cheaper than the $8 JJ cap cans.

[John]

Series doubles the voltage, but halves the capacitance (assuming equal cap value - otherwise it's the calculation you use for || resistance)
Parallel is the sum of the capacitance, voltage stays the same. So a 50 & 50 || will equal 100 uf, but won't double the voltage.
Don't forget to use the balancing resistors across each cap if you're putting them in series, they ensure that each cap gets roughly equal voltage.

[John]

It looks like I can get Cornell Dubilier Aluminum Electrolytic Capacitors - Snap In 100uF 400V 20% for about $2.51. These should fit onboard. Much cheaper than the $8 JJ cap cans.

In a 100W amp, you'll need to put those in series then, to give you enough voltage rating. Don't forget (which I'm sure you already know) on startup your voltage will probably surge.

[John]

Oh, one more thing: I'm not sure what perfboards are rated for voltage-wise, when it comes to arcing over the little pads? Sluckey or PRR probably knows. I googled that a while back because I was trying to make my cap board a bit more compact (compared to turrets) and shied away from it based on some replies I "read on the internet". 

[hesamadman]

The schematic I am using has a bit more filtering than some models.


http://www.davidsonamp.com/sm/images/JCM800mastervolumeM2203-100W.gif


The caps on schematic ARE 100u. They're already in series and have the balancing resistors. Some models have the CT filtered and some do not. This one does. I would imagine based upon this schematic that the 100u/400v caps I posted above should be more than enough. I will still use the 50/50 caps for two sections. This should cut cost in half.

[hesamadman]

Which now brings up a question in my mind. Why is there a centertap? If it is a bridge rectifier?

[hesamadman]

The basic question is, should be able to replace these 4 dual 50 caps with four 100u/400v caps correct?

[Willabe]

It looks like I can get Cornell Dubilier Aluminum Electrolytic Capacitors - Snap In 100uF 400V 20% for about $2.51.

Snap in caps are harder to work with than leaded caps.

I like the Mallory EE series radial caps. There about the same price with leads. Hi temp, hi ripple, low ESR, long life, small size.   

I get them from Mouser or DigiKey?

[sluckey]

The basic question is, should be able to replace these 4 dual 50 caps with four 100u/400v caps correct?

yes

[hesamadman]

Thanks Sluckey.

I like the Mallory EE series radial caps. There about the same price with leads. Hi temp, hi ripple, low ESR, long life, small size.   

I found some 350v ones for $2.50. Should still be sufficient. But what about this weird section connecting the B+ and CT?

[Willabe]

I found some 350v ones for $2.50. Should still be sufficient.

Yes, 700vdc, should be plenty.

Which now brings up a question in my mind. Why is there a centertap? If it is a bridge rectifier?

But what about this weird section connecting the B+ and CT?

The caps on schematic ARE 100u. They're already in series and have the balancing resistors. Some models have the CT filtered and some do not. This one does.

http://www.davidsonamp.com/sm/images/JCM800mastervolumeM2203-100W.gif

That's to force dcv balancing on the 2 caps. This way both caps see the ~same dcv. This keeps 1 cap from doing most of the work and/or seeing more dcv than it's rated for. It's not for filtering the CT.

Stacked filter caps would otherwise use a pair of R's (often 220K), 1 in || with each cap to force the balancing of dcv across each cap.

Connecting the CT to the junction of the 2 series caps does the same thing but saves 2 R's.

Also, you will get a higher dcv hooking up the CT to the stack then grounding the CT and using balancing R's with the same PT. So you can't just swap them at will. Gerald Webber (Kendrick amps) used to call it an 'economy voltage doubler'.

[sluckey]

It's very important that you get the proper power transformer for this project!

http://el34world.com/Transformers/files/BRITISH-Plexi-800-100W-PT.pdf