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Old 15th August 2019, 04:10 AM   #1
HarryY is offline HarryY  United States
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TU-8500  12AU7 vs 12A??
Default TU-8500 12AU7 vs 12A??

I'm considering trying something other than the 12AU7 (12AT7, etc).
I was curious as to what others have tried and the results the had.

Thank you

.
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Old 15th August 2019, 05:04 PM   #2
vkung is offline vkung  Canada
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12AT7 has the lowest impedance for TU-8500
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Old 15th August 2019, 05:26 PM   #3
rayma is online now rayma  United States
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Different tubes will require different values for the related plate and cathode resistors.
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Old 15th August 2019, 05:48 PM   #4
planet10 is offline planet10  Canada
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TU-8500  12AU7 vs 12A??
I have replaced the 12AU7 with 12BH7. I would not even consider AX7 or AT7 they are quite different, and as Rayma points out need differrent operating points. The BH7 might have higher heater demands.

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Old 15th August 2019, 06:22 PM   #5
vkung is offline vkung  Canada
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THE AMP IS DESIGN TO USE 5965A, 12AU7 AND 12AT7 ONLY.
Mr Fujita told me 12AT7 has the lowest impedance..
OF COURSE, you can use other tubes but his design is for 5965A, 12AU7 AND 12AT7 only
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Old 15th August 2019, 08:40 PM   #6
HarryY is offline HarryY  United States
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TU-8500  12AU7 vs 12A??
Quote:
Originally Posted by vkung View Post
12AT7 has the lowest impedance for TU-8500

How does it sound in comparison?
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Old 15th August 2019, 11:36 PM   #7
vkung is offline vkung  Canada
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From the designer point of view, 12AT7 is the best for TU-8500.
It has the lowest impoedance
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Old 16th August 2019, 05:43 PM   #8
HarryY is offline HarryY  United States
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TU-8500  12AU7 vs 12A??
Quote:
Originally Posted by vkung View Post
From the designer point of view, 12AT7 is the best for TU-8500.
It has the lowest impoedance

The 12AU7 has a plate resistance of 7,700 ohms
The 12AT7 has a plate resistance of 10,900 ohms

The 12AT7 is actually the higher of the two.

A better selection may be the 5751 with a plate resistance of 5,800 ohms.
That is if the TU-8500 can handle the higher filament current of
175 mA (at 12.6v) over the 12AU7 filament current of 150mA (at 12.6v).
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Old 16th August 2019, 05:59 PM   #9
vinylkid58 is offline vinylkid58  Canada
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TU-8500  12AU7 vs 12A??
Without a schematic of the preamp section, and how exactly the tubes are being used, this is all pretty much moot.

jeff
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Old 16th August 2019, 07:38 PM   #10
HarryY is offline HarryY  United States
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TU-8500  12AU7 vs 12A??
Quote:
Originally Posted by vinylkid58 View Post
Without a schematic of the preamp section, and how exactly the tubes are being used, this is all pretty much moot.

jeff

The schematic is in the manual
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