"refreshing" an old Carver amp. - diyAudio
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Old 5th April 2006, 06:23 PM   #1
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Default "refreshing" an old Carver amp.

I am the proud new owner of a Carver PM-900 amp that will serve duties powering a passive subwoofer that I am building.

The amp seems to operate perfeclty so far but I want to make a project out of this too so I thought it would be a good learning expirence to replace some of the capacitors as I know they have a finite life span.

I need to replace one capacitor for sure as it's top is domed. I beleive it is in the regulator circuit (or that's what it looks like from the diagram in the manual).

Then there are the 2 large caps. by the power supply. They are 9000uF 100V units. I have only seen a few with that measurement avail. online.

Can I use a 10,000uF cap. ? What effect does that have on the amplifier?

Now that I type this I realize that I'm less qualified to make these "decisions" than I thought, but I'm handy with a soldering iron!
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Old 5th April 2006, 10:19 PM   #2
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Well, I read some more after a few hours of searching I think I found a post similar enough to mine that it solves my question.

Anyone have any recommendations for an Electrolytic cap. manufacturer?
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Old 5th April 2006, 10:22 PM   #3
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Oh here's a picture too.


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Old 5th April 2006, 11:08 PM   #4
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Yes you can go to the 10,000uF capacitors. I would make sure that they are the same physical dimensions, since it looks like a very tight location. More capacitance (uF) simply means more energy stored and available when needed in the case when a capacitor is used in a power supply application. In timing (another DC application) and signal coupling (an AC reactance application) the size (i.e. in uF) is more critical and arbitrary changes in value are not recommended unless you are aware of the consequences those modifications might bring.
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Old 6th April 2006, 01:07 AM   #5
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Thanks. That's pretty much the conclusion that I had come to.

Now I just need to find some high quality replacements.
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Old 6th April 2006, 01:35 AM   #6
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Stick with the name brands suchas Mallory, Sangamo, Cornell-Dublier, etc (look through a Digi-Key catalog). Highly recommend the "computer-grade" series. My Crown DC-300A is over 25 years old and still has the original Mallory 13,000 uF computer-grade electrolytics.
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Old 6th April 2006, 02:17 AM   #7
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Oh cool. I found a Cornell-Dublier cap for $23ea. My budget allows a bit more than that but if they are respectable I can use the spare change to swap out the binding posts or something
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Old 6th April 2006, 01:07 PM   #8
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Hi Beat_Dominator,
Those caps are perfect. This is a triac regulated supply, so there is a lot of HF transients. You can try bypassing those. May as well change the other, smaller supply caps. There is more than one rail in there (three actually). Therefore you have two more pairs of capacitors to change. These are under harder use and tend to fail sooner than normal.

The only other suggestion I have for you is to make sure your AC connection to the panel is direct with this amp. Other components will not like the current draw off the line when you have it turned up.

-Chris
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Old 6th April 2006, 05:28 PM   #9
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Thanks for the input anatech. When I took out one of the 9000uF caps today I noticed one of the diodes on the board next to it is cracked in half . Good thing I pulled that cap though or I might have missed it.

Looking at catalogs I found this:

Cornell Type 500C computer grade cap. # 500C103U100AE2B

It is a 10,000uF unit but is the exact physical size of these 9000 units. Is that a good one to go with?
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Old 6th April 2006, 07:03 PM   #10
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Hi Beat_Dominator,
I didn't look the cap up, but that is a good brand. As long as the voltage is the same or higher you will be fine. The 10,000 uF rating is within tolerance of the 9,000 uF cap. Regard it as the same thing.

I can't remember what the temperature rating is on the originals. Make sure you get at least the same rating there too (85C or 105C).

Replace the other four supply caps while you are at it. They will have lower voltage ratings. You actually run on the lower rails most of the time, the high rails run earlier parts of the amp circuit.

-Chris
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