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Old 11th March 2012, 11:12 AM   #1
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Join Date: Feb 2008
Default Yaqin 100B fire and spares

My Yaqin went up in smoke last month.
The cause was one of the 180 ohm 3W screen grid resistors on the KT88s.
The standoff from the PCB is enough to allow it to contact the KT88 socket mounting bolt.
Eventually the insulation breaks down, resistor cooks up and melts the heater wire insulation.
Before I'd reacted half the PCB had burned away and the room was full of rather toxic smoke from burning PVC insulation.
Both HT + heater supplies survived so I tried to find a replacement PCB.
Not an easy task but this guy
hiendking hiendking [highendking"at"gmail.com]
sent one to France for 100 USD including P+P. He's a gem and strongly recommended.
The amp's up and running again, quite a tribute to the power transformer!
So, Yaqin owners, take the lid off and check those resistors.
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Old 12th March 2012, 11:56 PM   #2
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Join Date: Sep 2007
Quote:
Originally Posted by evetsfrance View Post
My Yaqin went up in smoke last month.
The cause was one of the 180 ohm 3W screen grid resistors on the KT88s.
The standoff from the PCB is enough to allow it to contact the KT88 socket mounting bolt.
Eventually the insulation breaks down, resistor cooks up and melts the heater wire insulation.
Before I'd reacted half the PCB had burned away and the room was full of rather toxic smoke from burning PVC insulation.
Both HT + heater supplies survived so I tried to find a replacement PCB.
Not an easy task but this guy
hiendking hiendking [highendking"at"gmail.com]
sent one to France for 100 USD including P+P. He's a gem and strongly recommended.
The amp's up and running again, quite a tribute to the power transformer!
So, Yaqin owners, take the lid off and check those resistors.
Sorry to hear about your troubles. I've had my share with this amp as well. Would you by chance have a picture to share of the damage the resistor caused you could share with us??

Cheers,
Bob
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Old 13th March 2012, 08:46 AM   #3
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Join Date: Feb 2008
You are looking at the two KT88 sockets and you can see the 180 ohm 3W screen grid resistor is touching the socket mounting bolt (arrow).
It has, presumably, arced then melted the heater wiring insulation. The heater wiring then caught fire.
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