Firebottle Kt88 tube rolling

[Bombadil]

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.

[Isaacc7]

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.

[Isaacc7]

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!

[decooney]

Originally Posted by Bombadil

...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. ...

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.

.

[Bombadil]

Originally Posted by decooney

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.

[Isaacc7]

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.

[Formerly YB-2]

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.

[Isaacc7]

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.

[Bombadil]

Originally Posted by Formerly YB-2

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.

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.

[Isaacc7]

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