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Old 24th August 2002, 09:58 AM   #11
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220 H is a capacitor 220pF. They look like the styroflex kind.
I guess they form an input filter. Check to see if one side of this
cap is connected to ground.
If it is, you could temporarly disconnect it, and do a quick test on an
speaker. If they are damaged, you will know.
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Old 24th August 2002, 10:49 AM   #12
2Bak is offline 2Bak  Denmark
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Top one connected to RCA cable shield, but not pcb ground. Second one connected to PCB ground. Should I disconnect both of them before testing with loudspeaker?

"If they are damaged, you will know." .... how?

thanks for nursing me ;-)
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Old 24th August 2002, 12:40 PM   #13
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Start disconnecting the one connected to the cable shield.

You will know the capicitor is damaged when the hauling stops.
(disconnected of course)

I still think you should perform the DC check first!
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Old 24th August 2002, 12:40 PM   #14
2Bak is offline 2Bak  Denmark
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jubii, it plays after having disconnected the top cap 220 H
It plays really like nothing is wrong with it even without the cab. Sweet music.
I'm flying :-)

Which replacements should I look for?
Is 220 H a TCP code?

There are three of these on each side, so I guess I should replace all of 'em.

The reason I didn't perform the DC-check is that I'm afraid to shorten my amp with my multimeter.

I would do this, like you described:

1. make the shortened RCAs and plug them in at input.
2. Connect my test speaker to terminals.
3. power on amp
4. put red multimeter pin on amps red loudspeaker terminal with speaker connected, and the black multimeter pin on amps red loudspeaker terminal with speaker connected
5. measure dc-voltage

is this correct?

Thanks again.
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Old 24th August 2002, 01:16 PM   #15
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I am happy to see the problem is located.
I do not know the exact meaning of the H on the styroflex cap.
My styro's all have a J marking. I suspect it indicates a
voltage range.

So, replacements should be 220pF either styroflex, (I do not like
them, to be honest) or Silver Mica.
Please do not use any ceramic disc type.

Also do not use the amp without them for a long time. Replace
them first.

DC measurement as you describe is OK.

Regards
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Old 24th August 2002, 02:43 PM   #16
2Bak is offline 2Bak  Denmark
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Found some Silva Micas at RS-Component's website I will order...

While I'm doing some soldering on the amp, I'll see if I can find other potential places to change parts hopefully making it sound better. Would like a little more bass control...

For example my four capacitors in the PSU, 10000uf, 50 v could possibly be replaced by new ones. The amp is nearly 20 years old, so they must be tired.
Also I could replace the film caps 1,5 uF for better typer, eg. Mcaps.
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Old 24th August 2002, 06:41 PM   #17
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If you like to change the input capacitors 1.5uF, you might
consider some nice Jensen Paper in Oil. Or Siemens MKV.

Also, if you plan to replace the PSU caps do not simply put more
capacitance in. The stress (charge peaks) could ruin the rectifier
bridge. And the whole amplfier and speakers for that matter.
Be sure you verify the max current for the bridge, before
you change the caps.

You could also decide on adding some nice bypass caps for the
10.000uF's.

Regards
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Old 24th August 2002, 07:01 PM   #18
2Bak is offline 2Bak  Denmark
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I plan stick to 10.000 uFs, 60v, not make it bigger.
Which bypass caps would you normally use for psu electrolyts? What would be the capacitance and voltage of a bypass cap for a 10.000uF?
For my Nelson Pass preamp I found some expensive Caddock resistors, for this power amp I don't believe I can find Caddocks. Any alternative if I wanted to change the power resistors?
Would replacing power resistors from mid 80's make any sence at all?
20 years ago the components of this amp were super, I'm not sure they are anymore...
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Old 24th August 2002, 07:50 PM   #19
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Bypass caps from 2.2uF to 10uF. I would use MKV. Only because
I have quite a few of them. When space is an issue, I would use
siemens MKP or FKP. The nice red ones.

I would not replace the resistors. Remember, you are very happy
the way the amp sounds right now. Especially using expensive
caddock's, holco's or allen bradley's. Lot of people rave about
old (+30 years) allen bradley's. I am not one of them.
I would however check or redo all the solder connections. Also
a carefull inspection of the PCB would not hurt.

If you are looking for a serious upgrade of your set, why not
replace the amp with a nice ALEPH?
You could go really overboard with such an amp. (Component wise, of course)
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Old 24th August 2002, 08:10 PM   #20
2Bak is offline 2Bak  Denmark
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I was planning to build an Aleph 3 to go with my new BoSoZ but I need to investigate more on Aleph 3 costs, pcb's, heatsinks etc before I proceed.
If I go for the Aleph, I will not upgrade this amp, except for these Silver Micas...or maybe even cheaper polystyrenes....

In fact I didn't listen to my BoSoZ yet because of my wiring mistake ;-)
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