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Old 27th December 2019, 10:07 PM   #1
Cifte12AU7 is offline Cifte12AU7  United States
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Default TU 8600 Red Plating

I have a TU-8600 300B amp with all of the upgrades (transformers, resistors, caps) but Gold Lion 300B tubes. One of the tubes is red plating.

Diagnosis and Prognosis anyone?
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Old 27th December 2019, 10:14 PM   #2
rayma is online now rayma  United States
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Check the tube first, but it could also be a coupling capacitor or a bad connection.
Did the amp work for a while, before the problem happened?

Last edited by rayma; 27th December 2019 at 10:23 PM.
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Old 27th December 2019, 11:19 PM   #3
nigelwright7557 is offline nigelwright7557  United Kingdom
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Either tube gone or problem with bias.
Check bias voltage at grid and voltage at cathode.
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Old 28th December 2019, 12:02 AM   #4
rayma is online now rayma  United States
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If you have to do trial and error, swap tubes and see if the problem follows the tube.
If not, it's below in the circuitry.
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Old 28th December 2019, 07:23 AM   #5
vkung is offline vkung  Canada
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Quote:
Originally Posted by Cifte12AU7 View Post
I have a TU-8600 300B amp with all of the upgrades (transformers, resistors, caps) but Gold Lion 300B tubes. One of the tubes is red plating.

Diagnosis and Prognosis anyone?
please check the reference voltages
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Old 31st January 2020, 09:26 PM   #6
gpdavis2 is offline gpdavis2  United States
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Cifte 12AU7 - what did you find out? Was it the tube or something else?
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Old 3rd February 2020, 04:44 PM   #7
Cifte12AU7 is offline Cifte12AU7  United States
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Strangely the problem stopped and hasn't resurfaced. But I pulled the unit from my current setup so I haven't had more than an hour on it since the problem started and then stopped.
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Old 7th March 2020, 01:02 AM   #8
Hmavv is offline Hmavv  United States
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Quote:
Originally Posted by Cifte12AU7 View Post
I have a TU-8600 300B amp with all of the upgrades (transformers, resistors, caps) but Gold Lion 300B tubes. One of the tubes is red plating.

Diagnosis and Prognosis anyone?
Yep! just like vk said. check your voltages! I wish the manual included tolerances. My 8600 ended up red plating a couple of times, each time was with Gold lion tubes. JJ tubes did better. But eventually a pair of gold lion fried aa few components on the left channel. my voltages were higher than the manual stated. I ended up using a step down transformer, 120 to 110, that's used in Japan. voltages came down to within a few volts of what the manual states, amp runs a lot cooler too. It's been almost a year and no more red plating
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Old 17th June 2020, 02:15 PM   #9
Cifte12AU7 is offline Cifte12AU7  United States
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Yes, I had the issue with Gold Lion 300Bs, but only one time and it's gone. I ran tests and didn't find any problem. Go figure!
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Old 17th June 2020, 02:35 PM   #10
vkung is offline vkung  Canada
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I recommend you to try the Black Plate 300B. This tube is inexpensive
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