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.

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.

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!

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?

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.

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.

Turns out the 2e22 has a max voltage of 250 volts on its screen grid. That is a ways below the 290 from the Firebottle. Oh well. It would have been fun to run a directly heated pentode. Though I'm not sure if a heater circuit not designed for directly heated tubes would cause audible problems.

I've been loving the Sylvania brown based 6sl7wgt with the 6ar6 tubes. An amazing combo. Thinking about what that 6sl7 had brought to the other tubes I figured it wouldn't work with the el38 tubes.

I was right. That combo was very clear, almost ethereal sounding but it lacked low end and felt flighty.

Finally got the 7c5 adapters and put in some NOS Sylvania clear 7c5 tubes with the Sylvania 6sl7wgt and wow. No, it didn't exhibit the hifi pyrotechnics of the 7n7/el38 combo or the weighty and warm presentation of the 7n7/6ar6 but I think the 6v6 tubes brought the most balanced sound I've heard from this amp. The entire spectrum high to low felt well represented. It is just ever so slightly warm but I think has that magic tube-type of neutrality.

If you can live with the 4 watts or so they give you should definitely try some old 6v6 tubes. I haven't done any direct comparisons but these Sylvania sound very much like the black glass Ken Rad 6v6s I used before. Even the really sought after 6v6 tubes aren't all that expensive, 7c5 even less. Check them out!

I know I've said it before but I really do think I'm done rolling tubes for a while. I've gone back to the el38 tubes, tall 7n7 input but now I'm using a Japanese 5ar4 instead of the 5u4g I had been using before. Oh, and I'm using this with my active preamp now.

I think this combo would be one of my go-to configurations if I was using a passive preamp. I also love the brown base Sylvania 6sl7wgt with 807, 6ar6 (with adapters), or sylvania 6v6, all with a 5u4g rectifier. The 807 and 6ar6 tend to be too warm and bassy when I use the amp with my 6sn7 based preamp.

Anyway, I do hope others will add their experiences with tube rolling!

The uber long thread of >6500 posts contains hundreds of posts from people telling of their tube rolling experiences.

On my KT88 HO extra hyped up Inspire, which produces 15-17 wpc instead of the standard 12, I like the big tubes best. KT88, KT120 and KT150. With some of the smaller, lower output tubes, they sounded strained and even harsh. 6F6, 6V6, and 6P3S-e all sounded harsh. To the point of where it was a pain to listen to them.

The KT88, KT120 & KT150 have the most neutral presentation, with a natural smooth sound but not overly warm. Good treble without being harsh. Good extended bass. All three sounded very similar. After a lot of comparisons, I decided I liked the KT120 best. I think.

Likewise for using a 6SL7. Extremely detailed and forward. Also tried a 6BX7 but didn't like it.

I have a number of 6SN7 which I like very much. The best of them create a wide, open soundstage with pleasant midranges and fairly strong, defined bass.

For a warmer, more bluesy sound, kinda a warm nightclub-like presentation, I like 1960s Sylvania fat bottle 6CA7s. Smaller soundstage, but warm & pleasant. Tried the new production EH 6CA7, they sounded overly warm and fuzzy. Less high frequency detail. Sounded like I set tone controls to bass +2 and Treble to -2.

For a punchier, edgier sound, which was still not harsh, I liked the new Gold Lion KT66. Electric guitars sounded a bit rawer. Horns had a little more bite, but just a shade. These can sound great on rock music.

Isaac7 wrote "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 haven't listened to the new 7581a tubes but four highly respected amp builders have told me that they love them. That they equal the quality of vintage 6L6GC and 7581a. Dave Gillespie has tested them and found that they meet all power specs and have very low distortion.

I have two quads of the new Genalex Gold Lion KT66, which are made in the same Russian factory but which are different. The GL KT66 draws 1.3A whereas the 7581a draws 0.9A and the internal construction differs.

I like the KT66 in my KT88 HO amp and even more in my PSE.

I would like to try the 7581a for at least a few minutes in my PSE to compare against the GL KT66, but I'm reluctant to drop $100+ for a quad when I'm not sure I would even like them as much.

Two people who have tried them all say that the new Tung-sol 7581a, KT66 (also 0.9A in the Tung-sol glass), and 6L6GC-STR all sound very similar.

Yeah, I started this thread because I think a lot of good info is buried in the monster thread. Ideally we’d have different threads for different topics so people can find the info they want.

The performance we get out of any particular tube will vary considerably with the load it sees and how loud you play. My phase tech PC 3.5 speakers sound like they are more sensitive than yours. Then again I rarely ever go above 82 db and I sit around 7 feet from my speakers so maybe I just don’t need as much juice. Which speakers do you use?

I have Von Schweikert tower speakers, which are essentially their old VR-7 model, but a bit customized by the original designer. They are 90-91 db. I sit 7' from them. Usually listen at 75-80 db, sometimes a bit louder.

Their strengths are throwing up a very large, transparent soundstage with a neutral overall balance. I've come to really appreciate the big image and so gravitate towards tubes & components which do the same. Likewise for the neutral bass, no measurable mid-bass hump at all. So any change which adds mid-bass warmth sounds tubby to me.

Likewise the highs are also neutral, no roll off. Some might find them too bright. So any tube combination which adds brightness starts to sound harsh to me. This has been the case for a number of tubes.

Interesting, my speakers are supposed to be around the same sensitivity. I'm guessing there is quite a bit of difference when it comes to the loads the amps see vs. frequency. I say that because I didn't find the KT88 tubes to offer me very deep bass, or at least not like I can get with other tubes.

Evaluating my output tubes on deep bass, for extension, definition and volume the KT88, KT120 and KT150 are the best in both my KT88 HO and PSE amps. I have some cuts with very low piano and string bass notes and I listen to hear the strings vibrating, clarity and fullness. With some tubes these passages the strings sound fuzzier and rolled off. With some tubes the higher mid-bass notes are overly prominent, tubby and forward.

My speakers have dual 9" woofers and go down strong to 32Hz with some output down into the low 20s.

My SS amps are even better on deep bass, going down deep with even better dynamics and definition. I don't consider deep bass to be the forte of a SE tube amp. I am satisfied if the SE amp can be reasonably good on bass while producing a glorious midrange and big, open natural presentation.

deleted duplicate post

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...

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!

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.

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!

Yes, some 6ez5 are a close equivalent to 6V6. I say some because the 6ez5 changed a bit over time. Early 6ez5 are a bit different, close, but different in some ways. They drew a higher heater current and had lower plate resistance.

However later production not only were close to 6V6, they *were* 6V6GA/GTA tubes. I've heard this changeover took place in the late 1960s into the 1970s. Tube manufacturers were cutting production and they decided to completely stop making 6ez5 and decided to substitute 6V6GTA, by labeling them as 6ez5.

You can tell them apart by measuring how much current they draw. If it is up around 0.8A to 0.9A, then they are authentic 6ez5. If they measure around 0.4A to 0.5A then they are 6V6GT/GTA.

If one is using an amp without much extra current capacity from its power transformer, say a PP 6V6 amp with 4 6V6 tubes. Then substituting 4 6ez5 can overload and fry your power transformer. So they are not safe substitutes for all amps. Shouldn't be any problem in an Inspire amp which can handle much larger tubes, such as KT150.

Interesting. I wonder if these are "real" 6ez5 tubes because they don't exhibit any glow on the plate when I power them with the 5u4. Everything I've read says that the 7c5 really is a 6v6 and I have to use the 5y3 to run them without glow.

I am planning a push pull 6v6 amp to be built for me so thanks for the warning! I will make sure there is enough headroom to use real 6ez5.

Back at it!
 

I’ve been loving the Sylvania 6ez5 tubes in the amp. I’m pretty sure they are actually GE grey plate 6v 6v6gt tubes but tube labels were more like approximations in the later days of production lol.

I switched out the tall sylvania 6sl7gtw with a clear RCA 6sn7 with a black bass and silver lettering. Wow! It’s a bit darker than the Sylvania but it has the same bass control and adds some “fatness” to the sound. Kind of like a thicker liquid sound I guess.

After a few weeks of that I finally got around to trying out one of my Ked Rad round plate 6f8g tubes. Compared to the RCA it is much more open and clear. Also bigger, almost like the whole soundstage has risen. The bass has maintained its solidity but now the darkness has been lifted. I will say that I found the additional clarity a bit fatiguing on some recordings.

I have since moved the 6f8G tubes into my preamp and put the RCA back into the Firebottle. What a combo! Woo! Unfortunately I forgot to switch my power setting on my preamp so I zapped the 6f8G tubes with 12v for several moments. Ugh. They do sound OK now but I worry I took years off of their life. SOB!

Bombadil, If you happen to recall, what attributes did you like more about the kt120 when comparing these three output tubes with each other? While I've owned all three of these output tubes in different amps at different times, reflecting back I realize that I probably did not spend enough burn-in time with kt120s or get to know them as well as I should have before i jumped to the KT150s. Anything more you can share about tone, texture, depth, lows, highs, "midrange" in a similar way you have with other types of tubes. Thanks in advance for your recall.

.

I did all of my previous comparisons in the Inspire Hot Rod HO, which is a super high output version which Dennis made few of. Produces 17 wpc with KT88, as compared to 12 with the "normal" KT88 amp. All while driving big full-range tower 91db tower speakers.

In that amp the KT88, KT120, and KT150 all sounded more alike than different. I liked all of them. I felt the KT120 had the best overall balance of deep bass strength and definition, good imaging & detail while not harsh, very good vocals, with a great open, natural sound.

I played Norah Jones' "Come Away with Me" in high res, the Holly Cole Trio "Don't Let the Teardrops Rust your Shining Heart" and Mark Knopler's "The Ragpicker's Dream."

In the end rather than identify each sonic characteristic, I went with the one which sounded most open & natural. Where I got lost into the music. I love hearing the deep acoustic bass strings, vocals coming out of a black background, instruments sounding separate and distinct. With that amp, the KT120 was just a touch better, although I thought the KT150 was better on deep bass and the KT88 was a touch better on vocals. No loser here.

By comparison my vintage Sylvania tat bottle 6CA7 were warmer with a smaller soundstage, but sounded more like a nightclub setting. Really like listening to blues with them.

Now I have an Inspire PSE and quads of each tube. And a new-to-me PS Audio DirectStream DAC with all of the latest upgrades (purchased used). Now I need to run many more comparisons. So far I'm really impressed with the new production Genalex KT66 on the PSE. It has a bite that makes music seem so alive. I've been working my way up from the bottom, starting with 6F6, 6V6GT, 5881, 6L6GC and now KT66. I've liked the KT66 best.

I made some changes upstream from my amp and now I'm going through different tubes again. I don't think I've mentioned my current input tube before. I really enjoy the Raytheon 6f8g. If the RCA 6sn7 sounds thick, the sylvania 6sl7w brown base sounds vivid, and the tall Sylvania 7n7 sounds warm, I guess I'd call the R 6f8g solid. Everything has weight and feels locked in.

I went back and tried the new Tungsol 7581a tubes and I thought they sounded kind of brittle. The new Gold Lion KT66 sounds really good with the R 6f8g. Maybe it's a bit "hi-fi" sounding, neutral instead off warm. For the warmth I'll pop the 6ar6 back in.

In wallet weight reducing news I sprung for a quad of the GEC E3375 tubes. They have the same connections of the EL38 but have the same plates and general construction of the legendary GEC KT77. I can't afford the GEC KT88, KT66, or KT77 so this purchase will be as close as I'll ever get to those. If nothing else it'll be nice to have a GEC tube in my collection lol.

While I do not have one of Dennis' new amps, I do listen to his 20wpc Class A PP Cary Rocket 88. I've rolled GL KT88s, GEC KT88s, GL KT77s, Tung-Sol 7581a & Tung-Sol EL34s. All have sounded great and I have listed them in the order I prefer them, though I would say if I gave them a rating out of 100 they would be 100, 99, 98, 98 & 97. The KT88s sound a bit more 'powerful' while the others all have a slightly sweeter mid-range for vocals. They are so close that I can happily listen to any of them.

Yeah, I have 3 or 4 combos I can enjoy. Still, it’s fun to try new things and see what kinds of sound my system can give me. I do have a general fascination with vacuum tubes and this amp has brought out all of my worst tendencies lol.

This is true for many of my tube sets. If I were starting again I would not buy as many as I have now. While there have been a few which I would place into a second tier, for the most part many sound similar. My KT88, KT120 & KT150 are very close. The GL KT66 & KT77 sound a bit different, a bit more "open" and a bit less power in the deep bass. My vintage 6CA7 are a tad warmer. All are very listenable.

My slew of other tubes don't sound quite as live/natural but many produce a pleasant sound, some more like a smaller venue stage or somewhat less high frequency detail. There are days when I like that, a more relaxing presentation. But even then it isn't a "night and day" difference.

I'd like to hear new Tung-sol 7581a as descriptions sound like I might like them. But to drop another $120 or so on yet another set of tubes just to satisfy my curiosity seems foolish. Same goes for spending big bucks to pick up vintage Mullard EL34 or Tung-sol 6550. I'm very happy with my current tubes.

There’s no question that from a listening point of view the amp does a wonderful job with a variety of tubes. I do enjoy the tubes themselves though and I love to hear what kind of an effect they can have on the sound. I’m cheap though lol. Since I don’t need a tremendous amount of power I can use tubes like the 807 instead of a 6l6c and save some coin. I also like “rescuing” tubes that are outside the mainstream like I’m saving strays or something. That’s why I use things like the 7c5 and the 14n7 in my preamp.

Whenever I wonder if I’m getting too weird about listening to tubes I pop over to the head-fi forums. I feel downright normal compared to some of those folks:) Think I have a good feel what going too far looks like now. I can quit any time I want! Lol

I am using KT-170, PSVANE 274B and KEN RAD CKR-6SN7GT/VT231 tubes. Speakers: Zu Audio Dirty Weekend MK.II, Pre-Amp: Roy Mottram SP14/Special V22. KT88's has a "Jazz Club" soundstage, Smooth in all ranges, Bass is controlled (deep) and a very imminent presentation. The KT-170's (after 10hrs) Opens everything up, Wider and Deeper Soundstage, the sound Floats around you. No need to tube roll at this time as this tube selection works very well.

KT-170 Tubes compatible with IFA-1 ?
 

I know this amp accepts KT-150 - will it interface with KT-170 tubes? If so, does anyone have any recommendations for a rectifier that will work well with the KT-120,150 or 170? (assuming the KT-170 will work in the IFA-1)

Sol-Tung… Welcome to AA! :wave:

Dennis has said you can use those tubes but don’t expect any more power than what the KT88 gives you. Dennis likes these tubes quite a bit in the amp, I haven’t tried them… yet. Lol.

I think the 5ar4 or equivalent is the rectifier to use for the high power tube. At ;east that is what is recommended for the kt88.

Thank you - so the larger tubes do not produce additional watts , however, is it true that additional headroom / dynamics may be a result of the larger tubes? I have KT-120's and they are nice, just pondering what the larger tube does ? yes, that's what she said....

There isn't any more power to give so no more headroom. They are different tubes so they are bound to sound at least a little different.

Sophia Blue KT88's
 

I have about 50 hours on a pair and they are sounding quite good.

I'm running them in a triode strapped Inspire amp that I bought from Dennis in 2016. So, this may not apply to non-triode amps. They sound like DHT's. :scratch2:

I'll post more after another 100 hours.

I would be very interested in comparing a SEP amp with a SET, using the same tubes. The KT88 is supposed to be really good as a triode. I've also heard that the 6v6 is supposed to be great as well but with a lot less power.

So the GEC E3375 is amazing. Clean, clear, articulate, if a little light sounding. When I combine them with an RCA 6bx7 the sound is remarkable. Looking at pictures it does look like the E3375 and the GEC KT77 have identical plate structures though they do bias up differently. If the KT77 sounds like these I understand why people consider them a holy grail tube. The E3375 cost a lot less than the KT77 though lol. Unfortunately they now seem to be unobtanium, I can't find any at all. Still, I now have 6 of them and that should do me fine, especially considering how many other great sounding tubes I own lol.

I will be getting in a bunch of 6aq5 from Brimar and a French brand I can't remember. Will also be getting in some Telefunken El90 which as far as I can tell are the same thing as a 6aq5. The 6aq5/el90/6005 is supposed to be a slightly downrated 6v6 in a 7 pin tube. Since I like the 6v6 tubes so much I figured I'd try these vaunted marques. They aren't very expensive so why not?

On the other end of the price spectrum I impulsively bought a pair of CV1102 tubes. Along with my E3375 these may be the most exotic tubes I'll pout in my amp. They have the same pinout as a gf8g but have a noticeably higher heater current. Luckily Dennis made the KT88 Firebottle able to handle the 6bx7 which is even more demanding. Anyway, looking forward to trying some GEC input tubes soon!

I just got in a pair of Tungsol 6c8g tubes. They have the same pinout as the 6f8 but have a higher mu. I have heard that these have similar sonic signature as the other round plate Tungsol tubes. I love my round plate 12sn7 Tungsol in my preamp and so I'm looking forward to hearing what these can do in my amp. Stay tuned...

@Isaacc7 : I am beginning to roll tubes in a June 2021-production Firebottle amp w/volume control, and am curious about your experience with 807/5933 power tubes and associated rectifiers. How does the 807 compare to say a kt88? I like the availability of the 807 and the quirkiness of it (adapter and top cap), but am curious about sound. I love more solid low end of the bigger tubes, but want to check out the 807 and any compatible retifier/input tube combo with it.