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Inspire by Dennis Had Enjoying Vacuum Tube Audio

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  #1  
Old 08-14-2021, 07:37 PM
Isaacc7 Isaacc7 is offline
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Default Firebottle Kt88 tube rolling

Because the KT88 Firebottle is a tube roller's dream I think it deserves its own thread. Too much info is buried in the monster thread, I hope this will be a place to share experiences with this particular amp.

My amp came with a Sovtek 5ar4, PSVane Kt88 Treasure, and a GE 6sn7. Out of the box my system (Topping D90, Schitt Freya+ passive mode, and Phase Technology PC 3.5 speakers) sounded very clear and open if just a bit hi-fi-ish. I have gone through a ton of tubes since. Here we go...

Yikes! This got really long. I'm going to split up the input and output tubes across a couple of subsequent posts.
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  #2  
Old 08-14-2021, 07:39 PM
Isaacc7 Isaacc7 is offline
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Default Input tubes

These impressions seem to mostly hold up regardless of which output tubes I use.

GE 6sl7
Sylvania 7f7 "chrome dome"

I found both of these to shift the emphasis up in frequency. While the 7f7 had remarkable bass control and extension ultimately I didn't enjoy the sound signature. It just gated on me and I found it fatiguing.

Sylvania 7af7. This is an odd tube not officially supported but I have heard of it substituting for 6sn7 tubes in other amps. It's gain is between the 6sn7 and the 6bx7. It's a round plate Sylvania tube so what the hell, I gave it a shot. I don't know if I just have a bad tube or if the 7af7 just isn't compatible but it did not sound good. Closed in, collapsed sound stage, grainy. Just bad.

My favorite input tubes have been various 7n7 tubes. As far as I can tell they are all Sylvania regardless of the label. Old Sylvania 6sn7 tubes are all well regarded and so I don't think you can go wrong. My favorite one so far is a tall bottle with a short silver getter on the top. From the 40s, it is open, balanced, and with impressive bass.

I have a slew of other conventional Sylvania 6sn7 and 6sl7 of various vintages that I plan on trying too. I'm actually hoping my 7n7 stash ends up being just as good. Then I can sell the regular tubes lol.

Last edited by Isaacc7; 10-01-2021 at 02:38 PM.
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  #3  
Old 08-14-2021, 08:28 PM
Isaacc7 Isaacc7 is offline
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Default Output tubes

As I mentioned earlier, the original KT88 tubes were impressive but I wanted a little more warmth and better bottom end. I have always had a soft spot for the 6l6 family of tubes. I told a friend of mine about wanting to try some tubes. He had a few sets of tubes in the 6l6 family that didn't suit his taste in his Elekit amp so he sent me his rejects lol. I ordered an EH 5u4g to get ready for them.

First up was a pair of 807 tubes with adapters. I had always wanted to hear 807 tubes so I was excited. They were unlabeled. My friend thought they were supposed to be Brimar but speculated that they were actually Russian tubes made in the 80s. They were dreadful. Thin sounding, screechy, and generally unpleasant. I told my friend and he said yeah, they were pretty much the same in his amp. I threw them away they were so bad.

The other set were much better. New Russian Golden Lion KT66. These had more of the warmth and "tone" that I was looking for. Now we were talking! Everything had more weight and sounded more natural to me. My opinion was further solidified once I replaced the GE with a 7n7 (see fist post).

I was happy with the sound but couldn't resist the siren call of trying other tubes in case they sounded better....

New Russian TungSol 7581a tubes slightly improved on the things that were important to me. a little better bass, little better guitar tone. Plus I felt comfortable using the 5ar4 with them for a bit more power.

I also ordered some new TungSol 6v6 tubes. Had heard good things about them. I wasn't too impressed with them. Pretty meh to me so I gave them to a guitarist friend of mine.

My friend felt bad about offloading his reject tubes on me and so ordered some 807 tubes from TubeDepot for me. Turns out they screwed up the order. He ordered the tubes he liked so much, Sylvania 5933. What they sent looked like proper 807 tubes (tall and curvy instead of short, straight, and squat like 5933). I had no idea they were the wrong tubes. They didn't have a manufacturer but were labeled CV 124. Ooh British! Were they Mullards? The 5u4g went back in and I fired them up. They certainly sounded like what I had assumed Mullards would sound like, big, warm, lush... I was in love!

Digging around I figured out they were Ferranti tubes. Also a British supplier, but it looks like these were actually Russian tubes. I think these are a screaming deal. You can get them for $15-$25 a piece. Well worth it if you like that kind of sound. Plus, they look amazing

Time goes on and my friend asks me if I'd be interested in some more of his "rejects" lol. His amp can take various tubes and I was benefitting from his experiments. This time it was the 6ar6. I had always been intrigued by these so was happy to try them out. Another winner! They resemble the 807s to quite a degree which shouldn't be a surprise. While they don't look nearly as good as the 807s they have better bass so they because my new standard. Keep in mind that even those these are octal tubes they are not plug and play! You need adapters in order to use them in the amp.

By this time I had been scouring ebay and tube sellers for more of those 807s, new input tubes, and now more 6ar6 tubes. I saw a pair of black glass Ken Rad 6v6gt tubes and ordered them on a whim. These sounded quite a bit better than the TungSol versions to me. Better bass, better depth, batter timbre. Still not as compelling as the 807 or 6ar6 though.

Once again my friend offered me another tube to try. This time they really were Mullards. I had never heard of the el38 before but wow, what a tube! First of all they are just sexy looking tubes. Still curvy like the 807 but taller. And they have the most prominent blue glow of any tube I have ever seen! But the real story is the sound!

In my amp, with the tall 7n7 input tube, and my speakers, the el38 gives me the best, well rounded sound of anything aI have heard so far. It has the clarity of the kt88 but better defined, possibly deeper bass than the 807/6ar6. The better details make the soundstage deeper. It's an impressive tube. It impressed me enough that I promptly bought out the rest off the Mullard branded supply of a UK tube supplier. I'm trying not to go into full on hoarder mode with this tube. I have never been this obsessed with a tube before, and that's saying something...

I prefer the 6ar6 when I want to rock out and the el38 for everything else. Man, I love this amp so much! So much fun!

Last edited by Isaacc7; 08-16-2021 at 10:28 PM. Reason: Point out the need for adapters with 6ar6
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Old 08-14-2021, 08:36 PM
Isaacc7 Isaacc7 is offline
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Default Tubes I'll be trying soon

I was happy to hear the Ken Rad 6v6 tubes sounded so good. I have a bunch of 7c5 Sylvania tubes I've been sitting on for over a decade. Back then I had DIY aspirations so I bought a ton of useful audio tubes with different bases and voltages. The 7c5 is a loctal 6v6 so it'll be fun to try them out. Just got the adapters in so stay tuned in...

I also had another tube put in my radar. The 2e22 is a directly heated pentode that appears to have the same pin out as the 807. Looking at the specs it certainly seems like it should be able to be run in this amp. I don't know if it being a directly heated cathode would screw things up though, I can't seem to find much info about popping it into a 6l6 circuit. Anyone out there have any ideas on the potential danger if any of doing that?

I also found some el39 tubes in my stash from years ago. I'm trying to figure out if they are suitable for this amp and if any of my current adapters could be used with them. Anyone ever hear of using these for audio?

Last edited by Isaacc7; 08-14-2021 at 10:31 PM.
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  #5  
Old 08-15-2021, 11:10 PM
Isaacc7 Isaacc7 is offline
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Default Sylvania 6sl7wgt

My previous experiment with a 6sl7 was promising but ultimately didn't satisfy. I had used a 7f7, a Sylvania 6sl7 with a loctal base. This particular one would be considered a "chrome dome" because the getter flash extended down most of the length of the glass. As a whole they have a great reputation but I found it fatiguing despite the fun of the bass extension and control.

While organizing my tube stash I came across a Sylvania 6sl7wgt with a brown base. The box said it tested at 70%. Popped it in and have been listening for most of the day. I am still using the 6ar6 outputs and the RCA 5u4g. My initial impression is one of smoothness. I don't hear the fatiguing sound of the previous Sylvania 6sl7 (7f7) but I got the bass back! Woo! This is my favorite tube so far, just edging out the tall 7n7 in this position.

Earlier in the day I had found a 50s vintage Sylvania 6sn7. It is a two hole cousin of the so-called three hole "bad boy" 6sn7. At least one of the online tube gurus (Brent Jesse? Andy at Vintage Tube Services?) claims they are sonically the same. In any case I wasn't impressed. Everything seemed subdued, I actually found myself wondering if I need a more powerful amp. There was also a dullness to the system that I wasn't used to. The 6sl7wgt replied this. Wonder if my positive views of that tube are because of my negative views of this one lol.
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  #6  
Old 08-16-2021, 10:32 PM
Isaacc7 Isaacc7 is offline
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Default

There's a twist with the 807 tubes. As I went through my tube stash trying to get it in order I found a pair of 5933 tubes. The only ones I would have had were the ones that my friend sent me. That also means that the 807 tubes I like so much are the ones I initially hated so much I decided to throw them out!

What changed? The only thing I can think of is that I got rid of the GE 6sn7 tube. The 807 tubes sound completely different than that initial session. It pays to experiment with both the input and output tubes. If you change one it's a good idea to see what changing the other can do for you.
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  #7  
Old 08-29-2021, 06:44 PM
Isaacc7 Isaacc7 is offline
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Default

My speakers can get down to 40hz or so. I agree with leaning into the strengths of SE amps. Right now all I have is the one amp though lol. So when one set of tubes gives me better bass I notice. Some of the other combos have been amazing for things like classical guitar but when I want to rock a bit I want to feel the bass.

Now that I have a preamp I like I anticipate getting a solid state amp too. We'll see how much I use it and for what. What a hobby...
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  #8  
Old 09-13-2021, 09:04 PM
Isaacc7 Isaacc7 is offline
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Default

I have been enjoying the Firebottle KT88 with 6v6 tubes. I have gone back to my old standby of the tall bottle 7n7. I had been running it with an RCA 5u4g but the other night I noticed a dull orange glow on the plates. Yikes! I have since started using a 5Y3 rectifier and that has taken care of the glowing plates. I haven't noticed a difference in the sound either. Listening in the dark is also a good diagnostic for amp operation!
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  #9  
Old 09-23-2021, 11:29 PM
Isaacc7 Isaacc7 is offline
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Default

I have dug up a tall Sylvania JAN 6sl7gt with the getter flashing in the bottom. This along with the Sylvania 6sl7wgt are my favorite tubes to go with the 6ar6/807. I will try the JAN 6sl7 with the 7c5 tubes next week but I think it's going to be a winning combo as well. I am using a passive preamp so maybe the extra gain is an advantage in my system.

I would encourage you to not assume all 6sl7 tubes sound the same, not even the Sylvania ones! I had previously used a tall 7f7 which is equivalent to the tall, completely chromed Sylvania 6sl7. The 7f7 felt a little hard and ended up being fatiguing. That surprised me because the 7f7 seems to have the same round plate construction as the JAN 6sl7gt. Both the brown base 6sl7wgt and the tall JAN 6sl7gt are much smoother. I think the tall JAN 6sl7 edges out the other one in both bass and overall tonal rightness. I guess it could just be the difference between these two particular tubes. In any case, both of these are widely available for reasonable prices and are worth trying.
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  #10  
Old 10-22-2021, 11:17 PM
Isaacc7 Isaacc7 is offline
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Default

New power tubes! My friend sent me some 6ez5 Sylvania tubes. They are supposed to be drop in replacements for 6v6 tubes. I'm now using an active preamp so my comparisons with previously used tubes are not going to be completely comparable but these seem to be noticeably warmer than the Sylvania 7c5 (6v6). I'm using the Sylvania tall bottle JAN 6sl7 and the tone is delicious. I dare say this combo is giving me the prototypical "tube sound" of being warm and a slightly loose bottom end. Guitars, acoustic or electric, sound amazing as does piano. Bass heavy music can get a little wooly.

Interestingly I can use these with a 5u4g rectifier without getting the orange glow like I was with the 7c5. You can get these tubes for $5 a piece, well worth it!
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