Newb assembling a TU-8660S

K

koenbro

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I am a newbie to audiophile stuff and have received my Tu-8600S kit today so will document here the journey of assembling it. Will no doubt have lots of questions, and looking at you all for help.

After an initial UPS hiccup yesterday the package was delivered this morning and it is very well packed -- triple packed actually. I read the manual and now am sorting the parts.
 
vkung

vkung

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Joined 2005
that is prefect...
Don't waste your time to check the part list.
The packing from ELEKIT will not miss a screw.
 
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K

koenbro

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IMG_2435.JPG


The kit is triple boxed. In this photo the outside box is barely visible on the right and left edges, with its flaps folded over. Shown are the sturdy middle and inner boxes.

IMG_2438.JPG


This is the entire content.

IMG_2439.JPG


Everything is very nicely packaged, the Lundahl transformers are in the white boxes at the right.
 
K

koenbro

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Have finished soldering the main PCB and the secondary PCBs as well. Will put it all together today after work and fire it up.

IMG_2459.jpeg
 
K

koenbro

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So I finished assembling the amp, and have several questions.

1. The measurements on one side are all off:

Measurements_warm.png


2. The tubes do not glow.

3. As noted in the measurements above, the speakers (brand new Klipsch Heresy IV) buzz when certain test points are touched.

When I first observed this, I stopped the system, disassembled it, and re-checked the PCB Unit-1. I did notice that component U-102 (LMV-431). was accidentally inserted reversed. So I desoldered it and reassembled it correctly. Not sure if it got burned up or not, can order a Texas Instruments replacement from Mouser. All other components appear installed correctly. I can take some quality photos of the PCB if that helps.
 
K

koenbro

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Immediately upon turning the system on, the voltages seem correct:

IMG_2467.JPG



But then 2 minutes or so into the warm-up the voltages on the left side (odd-numbered test point) drop rapidly to what I measured warm.


IMG_2473.JPG




I did swap the two ECC82 tubes but that does not make a difference in the sides.
 
K

koenbro

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The 300B tubes seem oddly rotated, meaning the label faces left. I paid attention to thick pin going into the bigger hole. I don't mind the esthetics of it but thought I mention it for completeness. The tubes are otherwise well seated. YOu can also see that they do not glow, 10 minutes into operation.

IMG_2476.JPG
 
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K

koenbro

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I am working through this.

The earliest problems is at TP29 where the voltage is about half of its counterpart TP30. Might there be a problem with the Power rectifier B, specifically diodes D102, 104 or PTC 101?
 
K

koenbro

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Results so far:

1. Immediately after turning on, all voltages are good.
2. If tubes are cold, voltages drop on the LEFT CHANNEL ONLY to values shown above after 3:30min.
3. If tubes have not cooled down to room temperature, voltages drop after 1-2 min depending on residual heat in tubes.
4. Swapping 300B tubes side-to-side does not make a difference.
5. Swapping ECC82 tubes side by side does not make a difference.
6. Removing the shared center tube ECC 83 does not make a difference.
7. I unsoldered U102 and U202 (LMV431) and swapped side-to-side. No difference. This test was justified by the fact that originally U102 was inserted wrong and I wondered if it is damaged. It likely isn't as the swap makes no difference.
8. I unsoldered PTC 101 and PTC 201 and swapped side-to-side. No difference.

Something happens after tube warmup that drops the voltage of the L channel but the tubes themselves, and the components above are not the culprits.

Any thoughts of what to look next? D103/104 swapped to the left?

Hopefully will be talking to Victor later today but curious if anyone has any suggestion.
 
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K

koenbro

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Ok, Victor @vkung you were spot on with your advice on the phone: I checked carefully the left channel components and one of the resistors was poorly soldered on. After I resoldered it, the system shows the correct voltages, balanced between right and left.

The system sounds sublime and have started the break-in.

Here is another vote of confidence in you, your products, and your service!

Thank you.
 
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