AB763 Twin filter cap question

[Randall]

A customer's blackface Twin Reverb I am tidying up has 22uf@500v filters where the schematic calls for 20uF@525v. There have been no PS issues with these in there. Would you recommend going up to 525v, or is 500v probably OK? I lean towards leave them in.

[Enzo]

The question to ask is what voltage are they exposed to in use? If the amp is running at 475 volts, then the difference between 500 and 525 volts is irrelevant.


I have to admit, I don't know when I last saw a 525v cap.

[Enzo]

Hey Randall, welcome to the forum.

Just a thought. It is not really good form to post the same thing in more than one section. Pick one, we'll see it.

[Randall]

I have to admit, I don't know when I last saw a 525v cap.

Yes, and therein lies the crux of the question. The amp is running under 475v, so it is getting filed under "if it ain't broke, don't fix it". Thanks again guys.

[Randall]

Hey Randall, welcome to the forum.

Just a thought. It is not really good form to post the same thing in more than one section. Pick one, we'll see it.

Gotcha. I was looking for an answer before I had to pick up parts tomorrow to get the amp out for the weekend, but I stand corrected.

[Leo_Gnardo]

What Enzo said. If that "blackie" Twin is 45+ years old, it's due for fresh filter caps. 500V rating will suit it fine. It's a terrific amp. You'll get many more years use out of it. Don't wait for half-century old caps to fail. It's called preventive maintenance. Also, replace the bias filter cap if that hasn't already been done.

[Randall]

Leo, you misunderstand. These are fairly new replacement caps that someone else already did. I would automatically replace original caps, that's a no brainer. I was just asking who here would yank these replacements and who would not. Personally, I like more robust looking HV filter caps, not the scrawny, probably Chinese ones in there now. Even if the values are the same, I just don't really trust the quality of something half the size of a Sprague Atom. And don't get me started about the absolute heinous connections in this amp. Someone went at it with bailing wire and stucco, looks like.

[Enzo]

Somewhere we have photos of Sprague Atoms - real ones from Sprague, current issue - and they are cut open to reveal the smaller cap that is packaged inside the Atom exterior.

[Randall]

Seriously?!

[Leo_Gnardo]

<Leo, you misunderstand. These are fairly new replacement caps that someone else already did. I would automatically replace original caps, that's a no brainer.>

Okey doke, with that explanation I do understand. Although I haven't seen any recently made caps rated 525V.

<I was just asking who here would yank these replacements and who would not. Personally, I like more robust looking HV filter caps, not the scrawny, probably Chinese ones in there now. Even if the values are the same, I just don't really trust the quality of something half the size of a Sprague Atom.>

For sh!ts n giggles try opening a currently made Sprague Atom. Inside you'll find a lot of stuffing - and a dinky capacitor. Just the kind you want to avoid. They know we pay plenty for quality, and they deliver this dreck. I'm off Atoms now. The old ad read "Don't be vague, ask for Sprague!" No more.

Lots of repair techs & builders are using JJ or F&T now. I get my hi voltage caps in quantity from Ruby (Magic Parts). I don't know who makes them, but the price is right, and I have yet to see one fail.

<And don't get me started about the absolute heinous connections in this amp. Someone went at it with bailing wire and stucco, looks like.>

Stucco!?! Ay caramba! Sorry to hear that. But if it's working & not turning out ultrasonic oscillation & hum... put it back to work. Button it up & get happy. It's Miller time! Or somethin' better if you got it.

[g1]

Could you post pics of "baling wire & stucco" ? Sounds tasty .

[Randall]

Wow, I had no idea about modern Atoms being posers. That really opened my eyes. I've never personally had one fail, but the bigger is better ideal is now on it's head when it comes to caps. But, the bailing wire and stucco quip was just a metaphor for extremely bad work, such as the new filter caps being soldered with globs of the wrong type of solder, and the leads wrapped around whatever was closest without trimming the ends. One stray lead was so close to touching the cap can I can't believe it didn't short.

[Leo_Gnardo]

But, the bailing wire and stucco quip was just a metaphor for extremely bad work, such as the new filter caps being soldered with globs of the wrong type of solder, and the leads wrapped around whatever was closest without trimming the ends. One stray lead was so close to touching the cap can I can't believe it didn't short.

Sounds like Ten Thumbs Tommy & his assistant Knuckle-draggin' Looie had a go at it.

[Leo_Gnardo]

Wow, I had no idea about modern Atoms being posers. That really opened my eyes. I've never personally had one fail, but the bigger is better ideal is now on it's head when it comes to caps.

Randall, Enzo, & other interested parties, I haven't found the capacitor caper yet on MEF but there was a mention just today on Audio Asylum about "Matryoshka" capacitors and it led to a 2010 thread at our friends "The Amp Garage". Some famous brands "with their pants pulled down so we can see what they really got." It ain't pretty. Have a lookee over here if you dare:

http://ampgarage.com/forum/viewtopic.php?t=10653&postdays=0&postorder=asc&start=0