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Old 19th June 2018, 07:52 AM   #1
jhedlind22 is offline jhedlind22
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Join Date: Jun 2018
Default TU 8200 problem

Today I turned on my TU-8200 and it sparked at CN9. (I learned this after disassembly.) I shut it off, and after some trial and error learned that Q3 is failed. The weird thing is that it appears the sparking occurred at pins 5 and 6 (heater voltage) on CN9. Also D7 has a low resistance from the + pin to the AC pin that connects to pin 6 on CN9.

It appears Q3 is responsible for the B+ left channel.

Another strange thing is that this sparking still occurred while no tubes were in the amp.

The tubes do not appear to be failed based on a crude multimeter check. I can't verify them 100% (no tube checker), but they don't have an internal short. It sounds like something is rattling in one of the power tubes, but it's the one from the right channel.

What normally causes one of those FETS to blow?

Is there a cascading failure I should worry about?

The associated Zener diode (ZD1) and diode (D3) appear to be fine. R51 is reading about half the required resistance, but I haven't isolated it in the circuit yet to verify this for sure.

Oh, and replacement parts. I need the FET at a minimum. When I looked up the data sheet for 02N60Z multiple models were listed. Does anyone know the correct model for this amp?

Does anyone know the correct model for the bridge diode?

The amp has about five months of trouble free use on it up until today. The driver tubes are the originals with the amps. The power tubes are 6550EH with about five months of use.

Thanks for any answers and help you can provide.
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Old 19th June 2018, 01:59 PM   #2
vkung is offline vkung  Canada
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If you need FET, I have replacement parts.Do you have another set of EH 6L6GC ?
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Old 19th June 2018, 03:20 PM   #3
jhedlind22 is offline jhedlind22
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It seems I do need a FET. Q3 has gone bad. Is this common? It also seems D7 has gone bad. I pulled it from the board and there is only 35 ohms resistance between the positive leg and the AC leg across from it. None of the other rectifiers read this low.

I have the set of 6L6 I received when I purchased the kit. They were used very little because I replaced them with 6550s.
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Old 19th June 2018, 11:14 PM   #4
vkung is offline vkung  Canada
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I have the parts in stock. or you can send your PCB for me to cheek for you
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Old 20th June 2018, 03:53 PM   #5
jhedlind22 is offline jhedlind22
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How much for the DB107 rectifier and the FET? What normally causes the FETs to fail? My amp has only about six months of use on it.

The tubes appear to be good by multimeter checks.

What normally causes one of those FETS to blow?

Is there a cascading failure I should worry about?

Jeremy Hedlind
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Old 21st June 2018, 07:03 AM   #6
vkung is offline vkung  Canada
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How much for the DB107 rectifier and the FET? less than $1

What normally causes the FETs to fail? bad tube

My amp has only about six months of use on it.

The tubes appear to be good by multimeter checks. ?? how can you use multi meter to test the tube set

What normally causes one of those FETS to blow? too much current ie bad tube set

Is there a cascading failure I should worry about? I only use new production tube set unless you have a vacuum tube tester
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Old 21st June 2018, 07:48 AM   #7
jhedlind22 is offline jhedlind22
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I ordered a new set of tubes because I am remotely located in Korea and I can't test the tubes on a tube tester here. I know you can't absolutely test a tube with a multimeter but I don't have access to a tube tester here.

How do I order the rectifier and the fet from you?

Jeremy Hedlind
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Old 21st June 2018, 01:46 PM   #8
vkung is offline vkung  Canada
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send your email to info@vkmusic.ca
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