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Old 19th May 2008, 07:04 PM   #1
Mywing is offline Mywing  Italy
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Default 400A: caps and spareparts

I ask who has been involved in restoring of a 400A his views and opinions on the various brands of electrolytic capacitors used to replace the old ones... Who has used Nichicon, Panasonic, Mallory, Elna and other brands could tell me impressions and opinions?

Then, I also would to know where I can buy some spare parts as the power on-off switch, a fuse cap and fuse holders.
Thanks for help.
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Old 20th May 2008, 08:13 PM   #2
Netlist is offline Netlist  Belgium
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Nino, does the amp work fine?
I ask because if it doesn't, I'd rather fix it before changing caps and other parts just for fun.
If it's working fine, no hum or noise, crackling or sparking , I see no reason to change caps.
If you can't resist the urge, go ahead but I am unable to provide info on Italian suppliers.

/Hugo
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Old 20th May 2008, 09:00 PM   #3
Mywing is offline Mywing  Italy
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Hi Hugo,
my 400A, as I described in another thread, works, but not fine.
It sounds hard, harsh, dry, woody, above all into mid-high and high frequencies... It's unearable for my tastes. I don't believe this is the real sound of the 400A.
Some mates (and Nelson too) suggested me to replace all the electrolytics, fuse holders and check the bias current...
Anyway I can purchase the caps in an overseas online shop (not necessarily in Italy...) I would only know a good very supplied seller.
Cheers,
Nino
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Old 20th May 2008, 09:13 PM   #4
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Did you just get the amp? Did you check the dc offset voltage
and bias after it has warmed up for an hour or so?
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Old 20th May 2008, 09:27 PM   #5
Mywing is offline Mywing  Italy
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I checked the bias in accordance with the instructions of Nelson: after an hour from switching-on the heatsinks' temperature should be 45-50 degrees. And it is right.
Cheers
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Old 20th May 2008, 09:35 PM   #6
Netlist is offline Netlist  Belgium
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Well, if Nelson said to change the caps, change the caps. He above all knows the Threshold best.

I tend to recommend Farnell as a reliable supplier.

/Hugo
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Old 20th May 2008, 09:49 PM   #7
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This kind of situation makes me nervous. We're asked to comment on modifications to a circuit that may or may not be working properly.
I see no reason not to replace caps, assuming that you are handy with a soldering iron and have access to decent parts.
From your e-mail:
--I gather that you're unsure about what voltage rating to buy when buying replacement capacitors. The answer is to buy a part that is rated for (at least) the same voltage as the part it is to replace. It should be printed on the part.
--I've got a schematic for this amp, but not it's not immediately accessible. There aren't any modifications I'd suggest under the current circumstances.
--You ask about increasing capacitance. In one place it sounds as though you're talking about the main power supply caps. In another you mention 22uF and 39uF caps, which are most certainly not power supply caps. It's hard to make recommendations without knowing what the capacitors do.
--I have no earthly idea what sort of power switch (or any other part) Nelson used in those days or where to get them...assuming that they're still being manufactured.
Your best bet will be to find someone who is at least somewhat experienced in electronics to help you. If you're determined to go it alone, I'd suggest that you begin by reading the other repair threads here that relate to your amp. Read all of them all the way through before attempting anything on your amp. It's best to go slowly so as not to make mistakes that could make things worse than they already are.

Grey
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Old 20th May 2008, 09:59 PM   #8
Zen Mod is offline Zen Mod  Serbia
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looking at attached pdf file - you'll see that 400A doesn't have mucho caps ........ but certainly have few worth changing and/or upgrading

if cap on input isn't your fave , change it with some polypropilen thingie ;

also - cap in feedback net (470uF) - put there some Elna Silmic or similar quality one , bypass it with nice little one - 220~410nF , polycarbonat or 'pilen,whatever

two 10uF jobbies ( up and down,,near rails ) - put , if nothing better , two little Wima's of 4u7/63V in parallel ,instead of one 10uF elko .

all other caps - under 100nF - replace them with mica or styroflex

main reservoir caps - have you anyone near you - with ESR meter ?

if you like to play safe - replace them with some computer grade caps, up to 3 times in capacity (maybe you'll need to increase mains fuse afetr that , but just slightly ; think about NTC in line with mains , if that part isn't already there .

bypass main reservoir caps with 1uF / whatever

edit:

I forgot to attach file

author of scan - look at file properties
Attached Files
File Type: pdf threshold_400a.pdf (51.0 KB, 89 views)
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Old 21st May 2008, 03:54 PM   #9
Mywing is offline Mywing  Italy
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Thanks for inputs guys.

Grey,
Quote:
Originally posted by GRollins

--You ask about increasing capacitance. In one place it sounds as though you're talking about the main power supply caps. In another you mention 22uF and 39uF caps, which are most certainly not power supply caps. It's hard to make recommendations without knowing what the capacitors do.
Grey
Sorry for trouble, I wrote 22.000 and 39.000: here in Italy and continental Europe . is for your , into numbers.
So I had write 22,000 and 39,000. Pardon, was been my fault...
Another thing:
do you think is it a good choise re-wiring some old inside cables or is at lost time?
Nino
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Old 21st May 2008, 04:07 PM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Mywing
Thanks for inputs guys.

Grey,

Sorry for trouble, I wrote 22.000 and 39.000: here in Italy and continental Europe . is for your , into numbers.
So I had write 22,000 and 39,000. Pardon, was been my fault...
Another thing:
do you think is it a good choise re-wiring some old inside cables or is at lost time?
Nino

you know what ?

I decided to help you with that bad amp - just send it to me , and I'll do proper disposal ........ it's old and even when new it wasn't great amp .......



if you see that insulation look old and brittle , and - if you see excessive oxidation on bare ends of cables - then replace them - with proper ( or audiofool type) ones .....

I forgot to tell you - regarding power switch - I can't really help you with that ....... I'm living in Serbia ........
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