Stacking Filter caps

Echoes

Senior Member
Messages
6,218
I need 22uf 525 vdc caps....if I stack a 2 uf 25 vdc soldered together with a 20 uf 500 vdc will that work to make 22 uf 525 vdc?
 

schmidlin

Member
Messages
5,257
No, it doesn't work like that. Others can elaborate if they want.

My suggestion: stop taking the old Fender schematics so literally and just plug in the 20@500.
 

WaltC

Member
Messages
2,126
the new F&T's are 22uF/500V, as are most of the Nichon/Illinois etc.. Close enough...
 

Echoes

Senior Member
Messages
6,218
Yea, reading capacitance in series/parallel tutorials I would limit voltage to 25 vdc doing it this way...
 

Echoes

Senior Member
Messages
6,218
No, it doesn't work like that. Others can elaborate if they want.

My suggestion: stop taking the old Fender schematics so literally and just plug in the 20@500.
I have 5 - 20 uf 500 vdc caps in there now and there's a noticeable volume drop.
 

cap47

Member
Messages
2,275
I have 5 - 20 uf 500 vdc caps in there now and there's a noticeable volume drop.
Put a 30 uf in it, doesn't have to be spot on perfect and don't obsess over the 25 V difference. I run a 30 uf in my 5e3.
 

Kyle B

Silver Supporting Member
Messages
5,102
I was thinking its the 25 vdc less per cap that's causing the volume drop...
That's not how it works. The voltage marked on the caps is maximum voltage that can be put on 'em before they meltdown.

Connecting them the way you describe would indeed create a 22uF cap, but you would also be putting ~400V across a 25V-rated capacitor. Your research is correct - you do not want to do this.

I have 5 - 20 uf 500 vdc caps in there now and there's a noticeable volume drop
Assuming these are in parallel you have created a 100uF 500V capacitor, which is too much capacitance.

Try a single 20uF 500V - that is within spitting distance of the original cap.

If that doesn't work, then I suggest you look very closely at your workmanship firstly. Generally one would not replace only a single EL cap.. Have you done a complete cap job or other work to this??? I suspect there's more to the story
 

GT100

Member
Messages
3,998
I was thinking its the 25 vdc less per cap that's causing the volume drop...
Dude. this and your original question makes me think you shouldn't be working on your amp.
A cap that is over voltage can explode...

Lloyd
 

Echoes

Senior Member
Messages
6,218
Dude. this and your original question makes me think you shouldn't be working on your amp.
A cap that is over voltage can explode...

Lloyd
I usually drag my amp down to my local amp guy....but' seeing as I now live in the sticks on the border of the end of the world that isn't always possible...

A) I don't have much choice
B) why do you think I'm asking questions and doing Internet research on this issue?
C) I am well aware of how dangerous these caps are...
 

Echoes

Senior Member
Messages
6,218
That's not how it works. The voltage marked on the caps is maximum voltage that can be put on 'em before they meltdown.

Connecting them the way you describe would indeed create a 22uF cap, but you would also be putting ~400V across a 25V-rated capacitor. Your research is correct - you do not want to do this.



Assuming these are in parallel you have created a 100uF 500V capacitor, which is too much capacitance.

Try a single 20uF 500V - that is within spitting distance of the original cap.

If that doesn't work, then I suggest you look very closely at your workmanship firstly. Generally one would not replace only a single EL cap.. Have you done a complete cap job or other work to this??? I suspect there's more to the story
I simply replaced 5 of the original early 60's 20uf 525vdc filter caps with Sprague ATOM 20uf 500vdc.......and I replaced the bias circuit cap from the old original 25uf 50vdc with the same value Sprague cap...

That's it....all soldering is tight and strong .....amp is now about 3/4 of the volume output than before I made these changes...

The reason I was thinking the voltage values on the filter caps was the problem is because THAT is the only thing that isn't to spec.....
 
Last edited:

CDA

Indigenous Donkey
Messages
349
If it's biased hotter you'll lose output power. Cold bias more power. ****** tone. But more power!
 
Messages
1,657
I simply replaced 5 of the original early 60's 20uf 525vdc filter caps with Sprague ATOM 20uf 500vdc.......and I replaced the bias circuit cap from the old original 25uf 50vdc with the same value Sprague cap...
Could've been a bad cap that you installed. Even new caps fail, and you don't know how old those "new" caps were before you installed them.

I would start over. 1) Put the old ones back in (only 12 solder joints), 2) play the amp (according to your work, it should sound like it did before you changed the caps), then 3) discharge the caps, 4) replace ONE cap at a time, 5) repeat steps 2, 3, 4 until all caps have been ruled out.

amp is now about 3/4 of the volume output than before I made these changes...
What issue made you want to change all the caps in the first place? Preventative maintenance? Or was there an issue that we (the readers) aren't aware of?
 

schmidlin

Member
Messages
5,257
I think the OP simply doesn't know the proper questions to ask.

Maybe you should have started with "I just made X changes and now I am at 3/4 power, what do I look for?"

If you want help I suggest:
-Tell us the amp and model#
-Give us your DC voltages on the power tube sockets
-Pics help A LOT

You need to start at the beginning...
 

mark norwine

Member
Messages
17,184
I think the OP simply doesn't know the proper questions to ask.

Maybe you should have started with "I just made X changes and now I am at 3/4 power, what do I look for?"

If you want help I suggest:
-Tell us the amp and model#
-Give us your DC voltages on the power tube sockets
-Pics help A LOT

You need to start at the beginning...
This ^^^^^^

And as long as we're chatting...

I have 5 - 20 uf 500 vdc caps in there now and there's a noticeable volume drop.
Your volume drop isn't because you went from 22 to 20 or any other such notion.

You have an as-of-yet undiagnosed problem, not related to the values of your power supply components.
 

pdf64

Member
Messages
7,940
That's assuming there really is a problem.
It may be that the amp is fine and Echoes has convinced himself that the 500v caps are limiting the output somehow.
It's easily done. I sometimes need to bench check kit just to prove that I was worrying over nothing.
 

Silent Sound

Member
Messages
5,418
How do you know that you're only getting 3/4 the power after the cap job? Have you measured anything, or are you just guessing based on how loud you think it sounded? Your ears can play tricks on you.

Either way, check you solder joints. Look for any loose wires. You may have broke a wire off somewhere where you weren't working by mistake. Did you swap out the tubes? Have you rebiased the amp? Especially when you're just getting started working on electronics, it's a good idea to just do one thing at a time and power the amp back up to make sure everything is still working. Replacing multiple parts at once can lead to a big headache if something doesn't go right. Take your time. Learn from your mistakes. Try not to get in over you head.
 






Trending Topics

Top