I've had the Kilo since May 2012. It gave me some trouble while I ran it in stereo mode. One channel stopped working after the first six months. I had it serviced through the
Sweetwater warranty by Hartke. It ran great in stereo mode again, but mono-bridge did not work. I played in stereo mode for about another year, then again another channel stopped working. Well, I had to pay $80 shipping (1st year was free shipping lol) to and from
Sweetwater. They replaced the damn PCB board. Now the amp has been working like it should! I am setup in mono-bridge mode with 2x15 Hydrives. I have four Hydrives, two are at band practice location, and two are home for self-practice. I have an Ampeg PF800 (superlight) for backup now since the Hartke Kilo failed to meet my expectations. So now, I don't have to haul amps from home to practice and back again. I guess, strangely, everything is working out as long as the Kilo doesn't have any more problems! I cased it and threw some rack fans on it for good measure. I would hate to give up on it, but if it continues to do its damn job, then I won't have to dump it.
Ok, so the Kilo comes stock with Sovtek 12ax7wa / 7025 preamp electron tubes. Those are some of the cheapest tubes on the planet, but they do well for their small price. I am looking for a richer sound by adding warmth to the mids and highs without overdriving the lows. There are hundreds of different types of tubes that could be rolled through the Kilo. Changing tubes will change the sound of the amp. The sound change may or may not be very noticeable.
I decided to give three TAD 7025s's a try. They definitely added warmth to the mids and highs, but it wasn't the sound I'm looking for. I am going to give them another month for sound climax before I decide to move on to some other tubes. I have the Preferred Series 7025 (set of three) for backup on deck. Both sets of tubes are the famous Mullard styles. I have a feeling the Preferred Series 7025 tubes will sound very similar to the TADs since they are basically the sames tubes, just different brands and testing.
I did alot of reading up on tube rolling. The Kilo has just three preamp tubes. From what I gathered, the tube setup might be similar to the Genz Benz Streamliners and the Gallien Krueger Fusions. Each have three preamp tubes. They don't have overdrive built in though. The Kilo comes with overdrive, which is pumped by the 2nd tube as far as I can tell. The first tube slot is near the input jack, and that tube makes the most noticeable audio differences in tone.
***I hope someone can explain in more detail how the preamp tubes in the Kilo are setup. That way, I can try some logical tube swapping, and maybe get a specific tube for each slot. There are many vintage new-old-stock (NOS) tubes available that probably perform better than today's current productions. I want to find the tubes that make people have eargasms$$$$!