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Old 11th January 2010, 04:34 PM   #1
urmoo is offline urmoo  Estonia
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Default Some more beginners questions about SSE

Seems, that it is not possible to edit earlier posts, so I start here new one with a bit wider subject.

Supplemental capacitor, is it OK to use 300 uF 400V cap? Another thing, probably stupid question- is it possible, that using supplemental cap improves signiffically sound quality? I could swear there is mutch more bass than earlier, without this cap...

STB switch is installed, lets see, if it will blow away rect. , for now everithing is OK.
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Old 11th January 2010, 06:44 PM   #2
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300uF is quite large. Is this an electrolytic cap? If it is rated for 400V *AC* line use, then it should be fine up to 560VDC or so. If it is just a normal 300uF 400V cap, then you are pushing the limit (depending on your actual B+, of course).

I found the putting a nice big film cap there made mine more "punchy" as well.
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Old 11th January 2010, 07:42 PM   #3
urmoo is offline urmoo  Estonia
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Yes, It is electrolytic cap, marked as 400WV 300uF with +/- polarity. B+ is actually around 450-460V, so not so good for cap, I guess... If it works near limits, should it warm up or is there other symptoms I should look for? Is 300uF OK, or will it start to give me somekind of troubles?
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Old 11th January 2010, 08:09 PM   #4
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The only concern I would have regarding a large capacitor would be the current rush at power on if you are using solid state rectification. A CL-90 thermistor should help there. Otherwise tube rectification should provide a soft enough start.

Correction: If you B+ is 450v your capacitor should be rated for 500v to be safe. If your running with 400v caps with 450v I'd expect cap life to be minutes and not hours.

Last edited by whitelabrat; 11th January 2010 at 08:13 PM.
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Old 12th January 2010, 12:52 AM   #5
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If it works near limits, should it warm up or is there other symptoms I should look for?
As I recently found out, sometimes the first indication that something is wrong is a BANG! A capacitor that big stores a lot of energy if it developed an internal short, it could explode rather violently. I would recommend disconnecting it immediately. See post #149 in this thread:

Posted new P-P power amp design

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Is 300uF OK, or will it start to give me somekind of troubles?
300 uF may make life difficult for your rectifier tube. I would look for something close to 100 uF. If it is intended for DC voltage it should be rated for 500 volts or more. If it is an AC cap it should be rated for 370 VAC or more.

If you happen to have two of your 300 uF 400 V caps they can be wired in series to make a 150 uF 800 V cap. Put a 100K to 470K resistor in parallel with each cap to equalize the voltage.

Quote:
Another thing, probably stupid question- is it possible, that using supplemental cap improves signiffically sound quality? I could swear there is mutch more bass than earlier, without this cap...
That is the reason that I recommend their use. It lowers the effective impedance of the power supply, so that more of your sound energy goes toward the speakers instead of going back into the power supply. I have found that a polypropelyne film (motor run) cap works better than a big electrolytic in this regard.
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Old 12th January 2010, 09:24 AM   #6
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Thank you for your replys! Your answers are proof, that If you dont know exactly what you are doing, then its better to ask for a advice Cap is disconnected and I will go to search for another one.
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Old 12th January 2010, 05:04 PM   #7
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Just to be on the safe side- does the connections look like this?

Click the image to open in full size.
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Old 13th January 2010, 12:18 AM   #8
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Quote:
Just to be on the safe side- does the connections look like this?
Yes, thats right
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Old 13th January 2010, 03:01 PM   #9
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Thank you for saving me from explosion Now caps are installed, and as result the sound is unbelieveably improved- excellent got even better! To be a rookie has some advantages- so many things can surprise

One more question. I use CFB pretty seldom, but today, after finishing installation of caps, I tested all functions of amp. Everything was OK, except CFT- switcing ON and OFF does not make any difference. I checked wires and solderings, they seem to be OK. Bad thing is, that since last time I used CFB I have done some replacements (Volume pot), then 5AR4 started to arch- short connection somewhere (dissapeared after disconnecting and connecting wires) and I have no slightest idea when CFB dissapeared (or perhaps it is constantly ON?). Is there any simple way to find out where CFB gets lost? I have a multimeter and dont affraid to use it
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Old 19th January 2010, 07:56 AM   #10
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Hmmm, OK, I will try to rephrase the question. Is it possible, that CFB has gone because some el. components are blown up (C12 and C22 for example)? If yes, how to check?
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