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Nakamichi PA 5E class A Stasis amplifier hum problem
Nakamichi PA 5E class A Stasis amplifier hum problem
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Old 8th February 2018, 07:21 PM   #21
classAchap is offline classAchap  United Kingdom
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Quote:
Originally Posted by Sixtron View Post
30 years old components should give me a reason :-)
No it isnít a reason, itís an urge.

Quote:
Originally Posted by Sixtron View Post
You think it is safe to remove this cables like you say and turn the amp on ?
Yes - if you understand what your doing itís perfectly safe. Have a look at the circuit, if you can understand what Iím suggesting you do, you can assess safety yourself. Please donít do it if you have ANY doubt at all.
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Old 8th February 2018, 07:37 PM   #22
classAchap is offline classAchap  United Kingdom
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Originally Posted by Mooly View Post
The 247 Vac has to be a measurement error or a faulty meter or a bad connection.

If you really did have that AC voltage present then there would be a hole in the ceiling where the caps just exploded through.
Of course there isnít 247 Vac across the caps - but this is what he says and it isnít entirely inconsistent with o/c caps is it?
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Old 8th February 2018, 08:27 PM   #23
Sixtron is offline Sixtron
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My opinion is that the multimeter is so sensitive that it measures the little spikes from the rectifier as AC voltage or the spikes are bigger and something is wrong.
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Old 8th February 2018, 08:50 PM   #24
classAchap is offline classAchap  United Kingdom
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Originally Posted by Sixtron View Post
My opinion is that the multimeter is so sensitive that it measures the little spikes from the rectifier as AC voltage or the spikes are bigger and something is wrong.
Well, thatís what we want to find out isnít it?

And Mooly is quite right, big caps can go off like small grenades, a colleague of mine was deafened for several days when one went off on his bench - it was one hell of a bang. So be warned - they donít like it upíem!
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Old 8th February 2018, 09:07 PM   #25
Sixtron is offline Sixtron
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Thank you, i knew it. This new one's have a protection valve. Maybe this should help to don't explode ?

I will try first the trick with the 10 Ohm hum brake resistor. Some people had success with it.
I have to order them. The circuit from my amp makes it easy to install them i think. Here i found a link to the pdf of the amp: http://www.creapromedia.fr/lesdocs/nakamichi/pa5.PDF
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Old 8th February 2018, 09:13 PM   #26
classAchap is offline classAchap  United Kingdom
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Originally Posted by Sixtron View Post
Thank you, i knew it. This new one's have a protection valve. Maybe this should help to don't explode ?

I will try first the trick with the 10 Ohm hum brake resistor. Some people had success with it. Here i found a link to the pdf of the amp: http://www.creapromedia.fr/lesdocs/nakamichi/pa5.PDF

Ok Sixtron, I hope it works for you, let us know - and yes, I have already downloaded the PDF.
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Old 8th February 2018, 09:26 PM   #27
Sixtron is offline Sixtron
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Thank you. Of course i let you know.
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Old 9th February 2018, 04:39 PM   #28
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Meanwhile waiting for the 10 Ohm resistors and small capacitors (i change them also) i have made the test to disconnect the four cables.
Measured voltages:

Left DC 64,7V Right DC 64,5V
AC over both 281V, even if i remove the power cord.

Cables connected:
60,6V and 60,4V
AC 267V

Btw. i had discharged the capacitors after this procedure with an oven lamp.
Bias i had already set before to 40mah like instructions say.
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Old 9th February 2018, 05:44 PM   #29
classAchap is offline classAchap  United Kingdom
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Originally Posted by Sixtron View Post
AC over both 281V, even if i remove the power cord.

Cables connected:
60,6V and 60,4V
AC 267V
What is the a.c. voltage you measure across C401, a) with the meter common connected to ground and b) with the meter live connected to ground.

What are the same measurements across C402 - that is, a.c. across the cap measured both ways.

You canít have 281V a.c. across a pair of 80V capacitors - not if theyíre in working order.
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Old 9th February 2018, 06:00 PM   #30
Sixtron is offline Sixtron
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c401 136v AC opposit 0v AC
c402 135v AC opposit 0v AC
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