I experienced a bad KT-170 in a pair I bought. I did not buy this pair from Victor but another private seller on the web. These were a backup pair for his amp that had never been used or tested in his system. Unfortunately I discovered one tube was fine, but the other produced a hissing noise that did not increase as the volume knob was turned. I swapped the tube from left to right channel and the hiss followed so I know it was the tube itself and not some function of the amp. The hiss was audible from my listening position when no music was playing
Also as the amp continued to heat up, the questionable tube did something odd that I haven't seen before in my limited tube experience. It seems like it became microphonic after being powered on for several hours. It would start amplifying either hum or vibrations from the transformer. As I would press my hand on the top plate of the chassis the hum would somewhat quiet down but then would reappear a short time later. The hum was not loud per se but extremely audible and could be heard when music was playing at normal volume. The seller offered a refund for this tube which was very kind.
I recently bought a quad of 2nd hand KT-170 from a different seller that all sound incredible and have no issues so far. I'm very pleased with the sound of the KT-170 now. So far I have tried the following power tubes and the KT-170 are by far my favorite:
1) A variety of new production EL34 tubes (Valve Art, EHX, JJ KT77/E34L, Mullard, etc)
2) Vintage RCA 6L6GC Black Plate -
3) Gold Lion KT88 -
4) Tung Sol 6L6G -
I will probably be selling most of these tubes if anyone is interested because my KT-170 sound so good. Will be interesting to try them all again after I roll in the Lundahl trafos which arrived earlier this week.
I just tried a set of KT-77s and they sounded real good as well. Next step is swap the KT-170s back in and see if the problem persists. It might be just one tube, I haven't really explored that yet. But it does sound like what you experienced. After about a half hour or maybe more the music starts to distort like the tubes are microphonic. Stay tuned for more.
Okay, I swapped the KT-170s back in and can't seem to duplicate the distortion I first heard. Problem solved? Still have the problem with RFI from my computer. I lined the case with copper foil tape and it had no effect. I put the steel top plate back on (was acrylic) and no effect. I'll try lining the top plate with copper tape. If that doesn't work I'm SOL. If I leave the volume on the amp at about 1/3 it's not audible at listening levels. I can adjust the volume on the preamp and it doesn't affect the volume of the noise. Once I get more than 1/2 on the amp the noise becomes quite obvious. I know it's the computer because as soon as I shut it down the noise goes away.
Located the source of the RFI. I had connected my PC to input 2 on my TU-8550 so I could listen to Youtube videos. It didn't seem to affect my TU-8900 but it was very audible in the TU-8850. Before I abandon that approach I'm going to try some ferrite beads and if that doesn't work I might try a better cable.
Lundahls sound great as expected. Low end is greatly enhanced, bass is textured, highs are more detailed and the soundstage now feels like it is projected out into the room and beyond the speakers. I now understand what Victor meant about the KT170 having 300B qualities in this amp. Very 3D and nuanced sound.
I have a very faint hum in the left channel but think that might be due to wire routing. Have to put my ear next to the tweeter to hear it. Will work on that today.
I have not installed the Vcap CuTF capacitors yet. One upgrade at a time. I am currently using some inexpensive Amtrans caps as a replacement for stock and they sound quite good for the price.
Also I'd just like to reiterate how awesome Victor is. We had a miscommunication about me wanting the acrylic plate shipped with the Lundahl. I emailed him and about it and he handled it. Shipped one out to me free of charge. Total class act. Thanks Victor!
I have a very faint hum in the left channel but think that might be due to wire routing. Have to put my ear next to the tweeter to hear it. Will work on that today.
I have not installed the Vcap CuTF capacitors yet. One upgrade at a time. I am currently using some inexpensive Amtrans caps as a replacement for stock and they sound quite good for the price.
Also I'd just like to reiterate how awesome Victor is. We had a miscommunication about me wanting the acrylic plate shipped with the Lundahl. I emailed him and about it and he handled it. Shipped one out to me free of charge. Total class act. Thanks Victor!
Just completed the build and completely dead silent. I had lined the case with Copper Foil as a RFI precaution. Burning in the Amp(150hrs) and will switch out KT-88's to KT-170's and will install Audio Note Copper Foil. I also upgraded the standard film (C108,C208) with Mundorf MCap Supreme.
Resistors: Audio Note Niobium Non-Magnetic Resistors (audio path), Amtrans AMRG
Resistors: Audio Note Niobium Non-Magnetic Resistors (audio path), Amtrans AMRG
Looks awesome! You are in for a treat when you swap in the KT170.
Which 12AU7 are you running? I've tried quite a few at this point and the Tungsram black plates have been my favorite so far. The RCA clear tops have been very surprising in this amp. Definitely my 2nd favorite for now. Did not particularly care for them in other amps I have used.
Which 12AU7 are you running? I've tried quite a few at this point and the Tungsram black plates have been my favorite so far. The RCA clear tops have been very surprising in this amp. Definitely my 2nd favorite for now. Did not particularly care for them in other amps I have used.
Thanks that would be great! Having a hard time zeroing in on which amp to build, Elekit or SunValley, add to that the KT170 run in SET vs 300B. The SunValley is very intriguing but a bit intimidating from a build point. While I'm pretty certain that I could build it having seen some professionally built, well....Also compounding the decision is that I listen to a wide range of music with a fair amount of rock.
Looks great! Are you using Belden speaker cables? I am considering buying a set to test with these amps!
Will put some thoughts together and share them soon. I've been going back and forth between the two amps this weekend.
Thank you. I'm using the belden wire from the crossover to each driver. I like the belden wire but I'm not in love with it. It took a long time to break in.
Looks like from the picture yours has the same problem as mine. The acrylic cover doesn't sit flush in the front middle. There's a small hump in the board for the volume pot that doesn't let the cover sit flush. I thought about sanding it down, but I think I'll just live with it. It's not noticeable with the metal cover because it's thinner than the acrylic.