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Output stage emitter resistors
Output stage emitter resistors
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Old 17th August 2019, 08:27 AM   #71
danny_66 is offline danny_66  Belgium
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Quote:
Originally Posted by Bensen View Post
Interesting paper Danny,
To bad those Isabellenhuette resistors are that expensive. €6 each. That would mean over €100 for my current amplifier.
They're also available in large SMD package (3W) from Distrelec for about 1-2€

Regards,
Danny
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Old 14th September 2021, 05:05 PM   #72
jason123x is offline jason123x  United States
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Default Pioneer VSX-523-K Emitter Resistor Types

Hi folks,
I'm new here and I would appreciate the help. I saw a long thread regarding resistor types on the Emitter stages, and I still don't know the answer.

I have a blown channel on my Pioneer amplifier. Some of the bad components were 0.47 Ohm Resistors (See Schematic and photos)

I'm trying to identify the type of these resistors to replace. I see some coating on the leads of these. Can anyone tell me what these are??
Label on schematic is 0R47(2), I'm assuming 0.47 Ohm @ 2W

They look like metal oxide. Do they have to be flame proof, coated, .. ??
Thank you
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Old 14th September 2021, 05:30 PM   #73
Mooly is offline Mooly  United Kingdom
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Output stage emitter resistors
Yes, 0.47 ohm. They do look like either metal oxide or wirewound type. If they have blown then the output transistors are almost certainly zapped as well. The resistors would not fail on their own.

Flameproof is part of the design brief. Often this is done because non flameproof types can burn and smell when they fail which of course can cause alarm to a customer.

It is your call what to fit although normally for this application we just use something of suitable rating and type.

https://uk.farnell.com/tt-electronic...219195?st=0.47

https://uk.farnell.com/multicomp/mck...903761?st=0.47
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Old 14th September 2021, 05:42 PM   #74
jason123x is offline jason123x  United States
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You are correct, both amplifiers were blown, resistors blown, caps popped,..

Thank you very much. I cracked one open, and it looks like it has film type material inside (solid ceramic like material)

I'd never seen coating on the leads of axial resistors before, so I'm not sure if that's critical? is it non-arcing ?
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Old 14th September 2021, 07:02 PM   #75
Mooly is offline Mooly  United Kingdom
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Output stage emitter resistors
I've seen the lead coating many times in general servicing but never really thought much about it tbh. I don't think there is much significance in it tbh. It is pretty common even in 0.25 watt ratings of carbon film resistors.

They are not critical at all beyond having to be 'low inductance' but given that 0.47 ohm means only a turn or two of wire they are automatically low inductance anyway.

I would advise you to use a DBT (dim bulb tester) when initially powering up the amplifier as it can save blown devices if there is a problem anywhere.
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Old 14th September 2021, 07:55 PM   #76
wrenchone is offline wrenchone  United States
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The lead coating is generally seen on parts that are formed for stand-up insertion. It can prevent adjacent parts from shorting together if they are bent over somehow.
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Old 14th September 2021, 08:09 PM   #77
jason123x is offline jason123x  United States
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Quote:
Originally Posted by Mooly View Post
I've seen the lead coating many times in general servicing but never really thought much about it tbh. I don't think there is much significance in it tbh. It is pretty common even in 0.25 watt ratings of carbon film resistors.

They are not critical at all beyond having to be 'low inductance' but given that 0.47 ohm means only a turn or two of wire they are automatically low inductance anyway.

I would advise you to use a DBT (dim bulb tester) when initially powering up the amplifier as it can save blown devices if there is a problem anywhere.
Thank you.. great idea on the DBT!!
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Old 14th September 2021, 08:11 PM   #78
jason123x is offline jason123x  United States
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Right on.. these are definitely installed standing-up. I just can't seem to find a resistor with that coating pre-applied. Is it something I can do to a regular resistor?

Wire jacket over it would do the trick, or does it get excessively hot?
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Old 15th September 2021, 05:08 AM   #79
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by jason123x View Post
Hi folks,
I'm trying to identify the type of these resistors to replace. I see some coating on the leads of these. Can anyone tell me what these are??
Label on schematic is 0R47(2), I'm assuming 0.47 Ohm @ 2W
Yes, it is 0R47 2W. It is better to use non inductive resistor here. Because inductance here can reduce phase margin so it reduce stability. I use metal film resistor.
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Old 15th September 2021, 06:07 AM   #80
Mooly is offline Mooly  United Kingdom
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Output stage emitter resistors
Quote:
Originally Posted by wrenchone View Post
The lead coating is generally seen on parts that are formed for stand-up insertion. It can prevent adjacent parts from shorting together if they are bent over somehow.
Thanks, I had never thought 'why' before

Quote:
Originally Posted by jason123x View Post
Right on.. these are definitely installed standing-up. I just can't seem to find a resistor with that coating pre-applied. Is it something I can do to a regular resistor?

Wire jacket over it would do the trick, or does it get excessively hot?
Does it really need it ? Once fitted they are a permanent fixture. Don't worry, just get some 0.47 ohm 2W and get them fitted

They do not get hot in normal use.
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