Tube Rolling w/Crack

[BNAL]

I just got some RCA 6AS7G black plates and on initial listening I find it to be a nice improvement over the 6080. I want to do some more listening, but for the price it seems like a no brainier.

[Laudanum]

I just got some RCA 6AS7G black plates and on initial listening I find it to be a nice improvement over the 6080. I want to do some more listening, but for the price it seems like a no brainier.

A Raytheon 6080 was included with my kit.  It's a nice sounding tube but I too immediately preferred the RCA 6AS7.  I also have a GE JAN labeled 6AS7 with copper shield (?) that sounds good too.  It's a smaller ST shaped bottle and that copper looks really cool/different.   But I thought that the RCA was a bit better.   Still running the 5998 though with a Sylvania 12BH7.  I think it's a nice combo.   I have a couple of the Russian 6H13's coming.  They were pretty cheap and I am curious as to how they sound.  Should have them in another week or so.

[BNAL]

I'm running the 5998 with a Mullard 4003 and like the combo. I tried the 5998 with a CIFTE 12AU7 and did not care for it. The CIFTE worked well with the 6080 though. I would like to get a CBS 5814A or even a 12BH7.

[Noskipallwd]

Brad, I think you would be happy with the CBS Hytron 5814a, I have one in my crack and my Cornet2 phonostage. It mates well with the 5998. It seems to smooth out some of the rough edges from the 5998s extra gain. I ordered the Eros, it uses the 12BH7 as a regulator, my friends that build guitar amps all said their favorite  is the Sylvania 12BH7A from the 50s. While I am waiting on the Eros maybe I'll roll it into the Crack and give it a listen. If you go for the CBS make sure to get the red label version.

Cheers,
Shawn

[BNAL]

Brad, I think you would be happy with the CBS Hytron 5814a, I have one in my crack and my Cornet2 phonostage. It mates well with the 5998. It seems to smooth out some of the rough edges from the 5998s extra gain.

Shawn,

Now that you mention it, that is what I thing was happening with the CIFTE. The Mullard seems to tame the 5998. I will has to give the CBS 5814A and Sylvania 12BH7 a try.

By the way I put the RCA 6AS7G and CIFTE back in and they pair nicely together.

Brad

[Laudanum]

Got two 6H13C's yesterday.  Grainy (maybe grungy is a better term) up top and mids are a bit recessed ... compared to 5998 which is clear as a bell.   Pretty decent bass though.   Both sound the same so it's not a bad tube.  These are NOS so they havent had any burn in.  Well, maybe 8 hours on one of them now.   Gave a quick listen again late last night and it's still about the same.  Tried a few different drivers 12AU7's and variants as well.   Im gonna give these a bit more time but Im pretty sure they arent my cup of tea.   I could happily live with any of the 6080's and 6AS7's that I have ... despite the 5998's being my favs.  And the few NOS that I have sounded good right out of the box.   These Russian tubes either need more burn-in or they are just kinda blah, atleast in my system.   Of course, YMMV.  

[dwilli852]

Got a Phillips Mini Watt ECC 82 today. Very nice sounding tube. Seems the bottom end is a little tighter and a small amount of improvement on the top end compaired to the EH 12AU7. Have a NOS RCA 6AS7 and Tung Sol 5998 on the way.

[Dr. Toobz]

Got two 6H13C's yesterday.  Grainy (maybe grungy is a better term) up top and mids are a bit recessed ... compared to 5998 which is clear as a bell.   Pretty decent bass though.   Both sound the same so it's not a bad tube.  These are NOS so they havent had any burn in.  Well, maybe 8 hours on one of them now.   Gave a quick listen again late last night and it's still about the same.  Tried a few different drivers 12AU7's and variants as well.   Im gonna give these a bit more time but Im pretty sure they arent my cup of tea.   I could happily live with any of the 6080's and 6AS7's that I have ... despite the 5998's being my favs.  And the few NOS that I have sounded good right out of the box.   These Russian tubes either need more burn-in or they are just kinda blah, atleast in my system.   Of course, YMMV.  

I have one of those 6H13C's in my stash, and can confirm your observations: they sound much warmer and grungier than a 5998 or even the usual 6080 that came with the kit. It's perhaps a good tube to balance a driver with a hot top end (like some 12BH7's or the RCA clear-top 12AU7), but otherwise, I find it rather lackluster compared to the 5998. Too bad those are getting so expensive as of late, though.....

[Dr. Toobz]

I should report that I now have an NOS Amperex (Holland) E80cc tube in the Crack at the moment. I like what I hear, but I can see where this tube might have its detractors: it's extended and very, very clean, almost to the point of sounding solid-state. When looking up THD figures on the internet for various 12AU7 variants, this seems to be verified by others as well: it's perhaps one of the lowest distortion small-signal triodes obtainable.

I will say that this tube has the best bass of any driver I've tried so far in the Crack.

[grufti]

I posted Crack measurements eons ago and I can confirm that with the E80CC in the circuit "all" distortion disappeared. Not really, of course, but the difference was very significant. There is still a pleasant balance between the 2nd and all the higher harmonics in the distortion spectrum.

[Dr. Toobz]

I remember seeing those great graphs you posted, grufiti - seems my ears would agree with your measurements. What's interesting is that as the distortion has been lowered in my amp (through better tubes and the CCS boards), I've experienced a more "solid state" type of impression of the sound - dryness, for lack of a better term - but on the other hand, there's still a realism that has evaded any solid-state circuit I've used or built. My theory is that the lack of NFB is responsible for the more open sound, and that perhaps a little bit of second and third harmonic distortion (say, on the order of a tenth of one percent) is "just enough" to enrich certain frequencies and give them a bit of heft and extended transient decay. With a good tube in the driver seat, the Crack seems to hit that sweet spot really well!

[Doc B.]

I'm inclined to agree that the proportion of 2nd to higher harmonics in an SE circuit with ZNFB could flesh out ( i.e. enhance) the tone of the original recording, but I don't see that it could be responsible for the higher resolution of the transient decay that gives one that sense of space and the venue acoustic that SE does so well. I think that is not an element related to harmonics but rather some very small signal temporal info that is somehow lost by the insertion of NFB. Of course others argue that it's simply microphony of the tubes that creates that sense of decay.

[Dr. Toobz]

I'm inclined to agree that the proportion of 2nd to higher harmonics in an SE circuit with ZNFB could flesh out ( i.e. enhance) the tone of the original recording, but I don't see that it could be responsible for the higher resolution of the transient decay that gives one that sense of space and the venue acoustic that SE does so well. I think that is not an element related to harmonics but rather some very small signal temporal info that is somehow lost by the insertion of NFB. Of course others argue that it's simply microphony of the tubes that creates that sense of decay.

I agree, but I still wonder about the role of harmonic content. NFB kills spatial cues, but it also reduces lower-order distortion, no?

For small, trailing-off sounds, like the last shimmers of a cymbal or high-hat, it would seem that boosting harmonic content (overtones) would raise the likelihood that the ear would still hear the sound where it otherwise would already have have disappeared under the noise floor or below the threshold of hearing. I've read somewhere that second and third harmonics are supposed to make things sound louder to the ear than the same pitch presented as a pure tone; some have claimed this is why SET amps sound louder and more dynamic than other topologies, watt for watt. The real test would be to see if a class-A solid-state amp with no NFB (like a single-ended MOSFET) produces the same effect, given the presence of a monotonically-decaying harmonic spectrum similar to that of open-loop triodes.

In any case, there seems to be no really solid explanation for why tubes sound so good! And the glow of the heaters just adds to the ambience....

[Paul Joppa]

You won't find a "class-A solid-state amp with no NFB" unless you make one yourself. Solid state devices have a current output, meaning high impedance, meaning no damping factor. The either use NFB explicitly, or they are emitter or source followers - lots of negative feebback, even though it's local and often enough not acknowledged. Just sayin' ...

Negative feedback actually increases higher order distortion, especially large amounts of it. Some think this is why is kills some of the life in music. (Yes I know that "life" is not a well-defined technical term!)

[BNAL]

I have been listening to the Crack with a 5998 and 4003 and it sounds very good. The only thing I don't like is that it does not use a lot of the volume control, maybe 10%. Even with the 6080 and 6AS7Gs I don't need a lot of increase in volume. Not sure if I should just leave it that way or add resistors to the input. I'm not a big on adding anything to the signal path though.

My source is a modded Squeezebox2, so it only puts out about 1v. Also, I'm using the stock potentiometer, but it seems to track well at the lowest volumes.