ELEKIT TU-8550 PRE-AMPLIFIER

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Joined 2005
@Catcherfly I plan to use the balance hole for this... Not sure if this is possible, but that's the basic idea. I dont think I will ever use the balance function (plan to hard wire it).

Pretty busy with daily work, so not able to spend time realizing this idea. But in general, I believe TU-8550 will be a nice upgrade from my TU-8500. So looking forward to build it.
 
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Joined 2024
Arizona is a oil cap and Jupiter is a copper cap
Vcap CuTF is copper too
CuTF is 2.3times of Jupiter
Jupiter is double the price of Arizona
The Az-cap is manufactured with aluminum foil, which is about 1/10 of the price of copper foil. CuTF is made with PTFE, which is 10x the price of the Jupiter dielectric.
 
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Joined 2021
I bought my TU-8550 a year ago and just recently had the time to put it together. After completing the kit, I'm having an issue with the right channel output. I've got some disconcerting readings: Test point 14 is showing -11.87V (should be 1V), TP16 is showing 196.2 (should be 125-145), TP18 is 160.9 (should be 110-130), and TP20 is 160.8 (should be TP18 + 2). I re-soldered all of those connections just to be safe, and checked the ohms on the un-powered resistors themselves (R224 (12k), R227 (100k), R228 (220k), R229 (47k)) and they all gave a proper reading. Sadly that's about as much as I know to do, does anyone have any suggestions of how to try and resolve this? Thanks in advance.
 
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Member
Joined 2020
I can't pinpoint it for you but if the left channel readings are good then something was installed wrong in the right channel. I would compare the two halves of the circuit board part-for-part checking not only the parts but their orientation.
 
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Joined 2021
Thanks - I actually wrote Elekit last evening not really expecting a reply and they got back to me already with a suggestion that it could be the heating element on tube V202, possibly caused by a bad solder joint on pins 4 / 5. I'll post again if that solves it.

-- upon closer inspection it looks like the tube itself is bad, there is white oxidation that I could not see before, presumably from a gas leak?
 
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Joined 2024
Just curious, what is the different between TKD and the original pots so it cant be used in the gain stage?
The original ALPS 4 channel pot has a linear variation of the resistance and TKD has logarithmic variation of the resistance. The TKD 4 channel pot can't be used in the TU-8550, because VR1 is linear (100k B) and mounted as voltage divider.
The TKD pot are "stereo volume (real log) control".
The ALPS datasheet mentions B version for tone & general (e.g. voltage divider) and A version for volume.
 
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Joined 2021
Managed to find a music store here with some tubes in stock, amp is working perfectly now. What a difference this makes to my 8800! Sounds phenomenal ... I wish I hadn't talked myself out of splurging for the nice capacitors from VK. Time to go for the 8900 maybe... Tube was a dumb oversight on my part, should have been looking more closely (oxidation was barely visible from the top... that's my story and I'm sticking to it), but it's good to know Elekit has such good customer service.
 
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Joined 2020
Glad to know it worked out. I can second the TU-8900 especially with the 2A3 tubes. It's the best sounding amp I own and I've got five tube amps.
 
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