Checked those oscillations and confirmed that with Lundahl, E80CC and EL12 spez there are no high frequency oscillations. The only signals I see at 500KHz and above are present with amp disconnected from power, so these are induced from external fields.

You cannot just stick tubes in without checking datasheet for compatibility. EL12 without top anode is not rated for anode voltage produced by 8200. EL12 spez has much higher voltage rating which is compatible with the amp. The problem with it is oscillations at around 1MHz. I’ll play with it to...

I think Lundahl is an improvement, I am definitely keeping mine. It was just about the only stock component I had left in my amp- everything else is not what came in the kit from Japan. I know Victor had worked a lot on making it happen, he tried different prototypes before he finally got it...

Yes I like EL12 a lot, even though it is not a fit for this amp strictly looking at the datasheet. But it sounds great and I have not had any trouble with it yet. My other big favorite is GEC TT21 which is similar to KT88. But I had trouble with a pair of TT21 after a while. GEC KT66 is very...

So I finally decided to swap output transformers in my amp which I got from Victor more than a year ago. Really like the sound! If money is no object this one is a recommended upgrade. Also parasitic noises went down to next to nothing. And it fits nicely with my big power transformer. Separate...

My TU-8500 has TDK pot which is better than ALPS. It was not as simple to install it as in TU-8200.

Thanks Victor! Layout looks familiar :)

TU-8500 is purpose-built as a preamp for TU-8200 and is a cute little project once TU-8200 assembly is finished. And it has good phono stage too. It adds a second pot, so you can control volume very precisely. And if you load it up it boosts 2nd harmonic and changes the sounds in a good way. But...

Did you use lead-free solder? That stuff is crappy- high melting point and good chance to get cold joints if you are not careful giving each connection point some extra heat time. And overheating components and traces is not healthy. I always use lead, and for Elekit assembly I used lead with...

I've got the same caps but I did not figure out how to stick them in. Did not like the idea of long wires to avoid picking up noise.

TU8200 is amazing. It is compact, it is versatile and it sounds really great! And also it is affordable. The base kit should cost more considering what's included and the quality. Yes, it stops being so affordable when all possible upgrades are applied to it. But it is one amazing amp, which is...

This is not about valves and not about power source. It is electromagnetic interference that is picked up by your system and amplified by the amp. You can reduce energy levels (e.g. increase distance to the source of interference) or improve shielding (this is not an easy task). Could also be...

DO NOT TRY THIS AT HOME well, you decide if you want to try this, but you've been warned :) seriously, this is not endorsed by Elekit in any way, they recommend against doing this. I wanted to try to drive a big 8 Ohm speaker and TU8200 did not sound too good. So I converted it into a...

I discovered today that EL12 spez excites in UL mode (likely capacitances in the tube with inductance of the portion of the output transformer) and oscillates at 400 kHz with fairly significant amplitudes. This phenomenon is volume-dependent, it does not happen at low volume but occurs sharply...

This is to document how hybrid opamp is installed with mixed up channels. The picture is upside down because it is taken from the back of the case- left channel is on the right. The top op amp is #1 and the bottom is #2 in these adapters. In the left channel (right on the picture) there is a...

Results of noise measurement on op-amps below. Measured using SPL1000 at the left speaker with TU-8500 and TU-8200 volume turned up to the max setting. original JRC 2068 DD - 54 dB OPA 2227P - 58.5 dB OPA1642 - 56 dB AD797/AD797 - 55.5 dB OPA1641/LME49990 - 55 dB LME49990/OPA1641 - 59 dB (this...

Traces confirmed what I measured earlier. Here are left and right channels below 1 kHz (100 Hz per division)- there should have been a bit more drop- supposed to be 19.35 dB: These are left and right from 1 kHz to 21 kHz- perfect 20 dB drop: These were measured across whole TU-8500-...

So I cleaned out phono section today: then soldered back better metal film resistors and low pass filter caps with polypropylene dialectric. Dropped input impedance to 47k. Back is now cleaner too- only bypass caps remain on the back side: Running frequency response traces now on the...

Regarding opamps- waiting for SOIC AD797 to throw into the mix. Will also flip one of the hybrid OPA1641/LME49990 at the same time. I looked into RIAA equalization filter to see where it is at. Shifted balance point using the additional resistor network at the top of the board and tuned one of...

Well here is a DUH moment- went poking into those opamps with oscilloscope and could not figure out why the output is different between the two channels until I noticed that the channels are wired upside down- right channel has second op amp as input stage while the left has the first op amp as...

Tried dual LME49990. Sound is awesome. As expected noise is slightly higher- at full amplification of TU-8200 I measured 60 dB at the speaker for dual LME49990 and 59 dB for hybrid OPA1641/LME49990 version (first stage gain is still suppressed to 50%). I think I will stick these into spectrum...

I think I am finally happy. Built a JFET/bipolar hybrid today- input stage OPA1641 at half gain and driver stage LME49990 at full gain. Hum is much more controlled than even with OPA1642 at half gain. Sounds great with Nagaoka MP-200, I like it better than OPA1642, which was in turn much better...

And now I am breaking in this beauty, arrived today from Japan. Tube rolling, op amp rolling, cartridge rolling... I guess speaker rolling is next :)

Had a musician friend visit me yesterday. Played his studio-recorded tracks via Gungnir Multibit and TU8500/TU8200 on LS50. He liked it a lot, said reproduction was excellent including both voice and drums. He was surprised by base actually. The tubes I currently have are Mullard 12AT7 in TU8500...

First experiment- JFET input with OPA1642. Sounds much better, finally I like the sound I get out of vinyl. Really noticeable improvement. The next step will be OPA1641/LME49990 hybrid where OPA1641 handles initial pickup from the cartridge and LME49990 drives the tube in the preamp. Might even...