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Old 4th May 2020, 02:54 AM   #101
transferfunction is offline transferfunction  United States
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Quote:
Originally Posted by vkung View Post
The successful rate for TU-8800 is very high. So far I only have one customer needed help
If you can send me the voltages, I can tell you what is the problem. Please do not do any modification until your amp is working properly.

Today the amp worked fine until I took it close to it's 10-12 watt limit, then the ripple filter shut down again (LED turned red for both channels. If the amp is turned off for a few minutes it will go back to normal operation (green LED). I also swapped in another good set of 12AT7 and 6550 and the problem repeated. Interestingly, if I change output tube to a 6L6 with power set to medium, the amp never shuts down, even into clipping.



As an aside, when I first powered the amp on I first did a thorough check of hiss and hum with my ear up to the speakers. Only very faint hiss with no hum at all, and it sounded dark & relaxed. After the first shutdown and ever since, there is now quite noticeable 60hz hum at the speaker, and the music sounds noticeably brighter. Maybe something has gone leaky of shifted out of spec in the ripple filter section?



Per your request vkung, I have take all TP voltage measurements in both normal operation, and with the amp's ripple filter shut down. I also took an AC millivolt reading at the output tube plates which showed 37mv in normal operation. Any help you can provide would be greatly appreciated.


Normal operation (green LED) All readings taken with a calibrated Fluke 289 DVM.
TP1 2.75 TP11 -32.1 TP21 5.24 TP31 389 - 390

TP2 2.71 TP12 -31.2 TP22 5.25 TP32 391

TP3 1.47 TP13 -32.2 TP23 360.2 TP33 391

TP4 1.44 TP14 -31.2 TP24 360.1 TP34 -70.8

TP5 149 TP15 4.41 TP25 360.5 TP35 6.61

TP6 147 TP16 4.42 TP26 360.6 TP36 7.33

TP7 120 TP17 -54.9 TP27 377.0 TP37 7.05

TP8 121 TP18 -54.9 TP28 377.0 TP38 6.71

TP9 270 TP19 3.27 TP29 11.1 - 12.5 TP39 26.4

TP10 270 TP20 3.27 TP30 11.0 - 12.5 TP40 236.8

TP41 69.8


With ripple filter shut down (red LED) both channels
TP1 .593 TP11 -10.78 TP21 .03 TP31 441.0

TP2 .577 TP12 -10.70 TP22 .02 TP32 441.0

TP3 .165 TP13 -10.80 TP23 61.9 TP33 441.0

TP4 .179 TP14 -10.75 TP24 62.0 TP34 -73.4

TP5 16.37 TP15 .03 TP25 61.9 TP35 6.82

TP6 16.28 TP16 .02 TP26 61.9 TP36 7.55

TP7 22.92 TP17 -54.8 TP27 62.0 TP37 7.10

TP8 21.79 TP18 -54.8 TP28 62.0 TP38 6.80

TP9 41.7 TP19 3.27 TP29 378.9 TP39 26.72

TP10 41.7 TP20 3.27 TP30 378.6 TP40 246.7

TP41 73.0
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Old 4th May 2020, 04:48 AM   #102
vkung is offline vkung  Canada
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I have a feeling you are using the 100V power PCB board. There are 2 boards inside the BOX. You should use the 115V PCB Board
Why you turn the amp to the limit???

If your measurement according to the step from page 22, you have a very high voltages compared to the reference voltages. The readings are abnormal .
Are you setting the current to high?

For PT 31 you have 389V.. It is impossible.

With ripple filter shut down (red LED) both channels
I do not understand why you are doing this step....
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Old 4th May 2020, 09:02 AM   #103
transferfunction is offline transferfunction  United States
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Quote:
Originally Posted by vkung View Post
I have a feeling you are using the 100V power PCB board. There are 2 boards inside the BOX. You should use the 115V PCB Board
Why you turn the amp to the limit???

If your measurement according to the step from page 22, you have a very high voltages compared to the reference voltages. The readings are abnormal .
Are you setting the current to high?

For PT 31 you have 389V.. It is impossible.

With ripple filter shut down (red LED) both channels
I do not understand why you are doing this step....

I am using the 115 volt power connector board. While waiting for a pair of Tekton Lore, I am using Spendor LS3/5A 11 ohm. They are only 82db efficient, which is why I am running the amp close to 10 watts.


Those voltages are indeed too high and likely the reason for hum through speakers and ripple filter shutdown. I included readings with the amp in ripple filter shutdown just to be thorough. Also attached are images showing TP 31, 32 & 33 being measured in normal operating condition.
Attached Images
File Type: jpg IMG_0353.JPG (160.9 KB, 140 views)
File Type: jpg IMG_0360.JPG (160.8 KB, 141 views)
File Type: jpg IMG_0365.JPG (177.9 KB, 140 views)
File Type: jpg IMG_0370.JPG (172.5 KB, 142 views)

Last edited by transferfunction; 4th May 2020 at 09:13 AM. Reason: Additional info added
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Old 4th May 2020, 02:53 PM   #104
vkung is offline vkung  Canada
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Please let me know the reading of
TP 40
TP 41

Your FET filter is working but TP40 and TP41 are two high
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Old 4th May 2020, 02:59 PM   #105
vkung is offline vkung  Canada
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I need to chat with you later today
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Old 4th May 2020, 09:38 PM   #106
transferfunction is offline transferfunction  United States
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Quote:
Originally Posted by vkung View Post
Please let me know the reading of
TP 40
TP 41

Your FET filter is working but TP40 and TP41 are two high

Measured voltages again today. With amp in normal condition (high power mode), TP40 is 236 volts, TP41 is 70 and TP33 is 390 . These results were with an AC mains input voltage at 123.


I suspect one of two scenarios may have occurred. When the wall outlet voltage is closer to 125 (US and Canada nominal is 120V +/- 5%) AND the amp is run close to it's rated output in high power mode, the ripple filter design parameters are exceeded. Another possibility is the power transformer or a component is slightly out of spec, causing shutdown of the ripple filter under these conditions.



I understand that the ripple filter is still working however, there is now a constant low level 60hz hum out of both speakers after that initial shutdown.
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Old 4th May 2020, 09:57 PM   #107
vkung is offline vkung  Canada
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5-10% is acceptable. There are 2 scenarios
1. R-core issue? it is very rare the problem from the Japanese R-core. I have never encountered
2. PCB issue?

I will consult Mr Fujita.
It is Golden Holiday in Japan

"however, there is now a constant low level 60hz hum out of both speakers after that initial shutdown."
This constant hum is the FET problem.
Do you have a FET tester?

Last edited by vkung; 4th May 2020 at 10:04 PM.
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Old 4th May 2020, 10:23 PM   #108
vkung is offline vkung  Canada
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I can chat with you? Do you have face time or What apps?
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Old 4th May 2020, 10:58 PM   #109
transferfunction is offline transferfunction  United States
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Quote:
Originally Posted by vkung View Post
I can chat with you? Do you have face time or What apps?

I do not have a FET tester unfortunately, and speaking of which, the amp does appear to shut down at slightly lower volumes now also. The I still use a flip phone so no face time or what app available.
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Old 5th May 2020, 01:00 AM   #110
vkung is offline vkung  Canada
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email your phone number to info@vkmusic.ca
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