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Broken bias resistors (Yaqin MC-10L)
Broken bias resistors (Yaqin MC-10L)
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Old 20th March 2014, 07:05 PM   #1
icc87 is offline icc87
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Default Broken bias resistors (Yaqin MC-10L)

Hello there! I'm new here and I've had this Yaqin MC-10L for almost a year now. (the one with bias adjustment holes in the cover)

The other day there were some cracking in the speakers and I saw some white flashing from the tube positioned at V1. So I pulled out my voltmeter and found that the voltage between the bias measurment holes were somewhere in between 50V and 60V(!). I powered down and removed the tubes and cover. I measured the resistor next to each valve and concluded that the resistor at V1 and V4 were dead.

Any ideas to why or how this happened?

I'm thinking of ordering some new resistors, would it be wise to go for some that are 3W or 5W instead of 2W?

Regards
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Old 20th March 2014, 09:17 PM   #2
euro21 is offline euro21  Hungary
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Broken bias resistors (Yaqin MC-10L)
V1 and V4???
These are in different channel!
See the schematic:
YAQIN MC-10L
http://nice.kaze.com/mc-10l_12.pdf
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Old 20th March 2014, 09:24 PM   #3
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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More than likely, if the 10R have failed it is due to Chinese EL34s flashing over inside. Can you confirm the resistors that have failed please?
10R 2W is good for 200mA. EL34s should conduct no more than 150mA as an absolute peak. A larger resistor will mean the valve will destroy itself rather than the resistor.
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Last edited by JonSnell Electronic; 20th March 2014 at 09:27 PM.
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Old 21st March 2014, 07:28 AM   #4
icc87 is offline icc87
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Yes they are indeed on different channels. But I didn't notice the V4 until after the V1, so it might not have happened at the same time.

I'll try replacing the resistors with 2W's then, and pop in some Tung-Sol el34b valves that I bought last fall.

Thank you for your input!
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Old 21st March 2014, 07:32 AM   #5
icc87 is offline icc87
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There's absolutely no current going through the resistors. They're marked NE05 10 Ohm, and I belive they're ceramic.
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Old 21st March 2014, 06:46 PM   #6
patkhan1 is offline patkhan1  Chile
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Search the threads, there are at least 2 on this site with extensive information about the same problem. The same happened to my MC10L, after replacing resistors and valves, it's all good.
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Old 3rd July 2017, 08:44 PM   #7
marty136 is offline marty136
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I had the same problem occur with my mc -10t. did you replace just the bad ones or all. could you please share the spec on the bias resistors? thanks! marty
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Old 4th July 2017, 01:59 PM   #8
icc87 is offline icc87
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I ended up using Akanehm's 10 Ohm 2 W 2 % (RSMF2TB 10R G PB-FREE) to replace all four. They've been working beautifully ever since.
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Old 4th July 2017, 03:49 PM   #9
marty136 is offline marty136
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Default thanks

thanks for the info. i replaced the broken one yesterday with what i could find local and system is working fine. ordering 4 quality units today. going down to 2w is a great suggestion. the other suggestion i got from stereo repair man was to stop using low end chinese tubes. step up to their good stuff or go russian.

happy 4th of july,

peace..
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