Tube Rolling w/Crack

[Laudanum]

The 5998 was reportedly of particular benefit with the 601's leaner bass because of the lowered output imp. of Crack when using this tube.

I may be wrong here, but it is my understanding that a lower output impedance will actually reduce the bass. When calculating the cutoff frequency, the output impedance is in series with the load - and lower impedance increases the cutoff. The benefit from a lower output impedance is an increase in the damping factor - so whatever bass is there should be tighter.

Its a careful balancing act between these opposing effects, and really comes down to personal taste.

That should be right according to a related response by Paul J. to a question I had a while back.  I had forgotten about it.  The higher damping factor would explain my hearing the tightened bass.  That said, I dont think there was any real decrease in bass, not audible anyway.  But being a matter of cutoff frequency being raised, not actual reduction of the entire bass frequency range, it wouldnt necessarily translate to an audible decrease in bass anyway.

[Paul Joppa]

I did some calculating, based on the published curves and specs, a while back. In the stock circuit, the output impedance of a 5998 is 80% of the 6AS7 impedance - quite a small difference, in spite of what the difference might be at the operating points cited in the data sheets. I doubt the impedance is the reason for the sonic difference.

I and a few others around here have heard these tubes as straight amplifiers (preamps) with the output taken from the anode. In this case, the 5998 has a higher output impedance than the 6AS7, and the broad consensus is that it still sounds superior.

I wish I knew why.

[Noskipallwd]

Hello,
I'm fond of the 5998 myself, it performed well in just about every amp I have heard one in. Folks try to tell me that the WE 421A is a better tube. They don't seem to appreciate it when I tell them that the 421As are all rebranded TS 5998s. Has anyone ever rolled an Amperex 7316 in this amp, or has anyone ever heard one in other equipment? I've heard raves about this tube but they are rare and cost half as much as the Crack. Probably won't ever buy one, just wonder if they sound as good as people say.

Cheers,

Shawn Prigmore

[Beefy]

Folks try to tell me that the WE 421A is a better tube. They don't seem to appreciate it when I tell them that the 421As are all rebranded TS 5998s.

To be fair, I have heard a convincing argument that 421A tubes were 5998 tubes specifically hand-selected for high transconductance. Sure as hell doesn't justify their extra price to me though......

[Noskipallwd]

To be fair, I have heard a convincing argument that 421A tubes were 5998 tubes specifically hand-selected for high transconductance. Sure as hell doesn't justify their extra price to me though......

That's interesting, I hadn't heard that. Sounds feasible though, I wonder how much variation in transconductance there can be amongst tubes made with the same manufacturing methods. Maybe someone with a little experience could enlighten me. I agree that the price difference is nuts. Of course supply and demand drives that, and somebody is willing to pay otherwise they couldn't charge that much. Same with the Amperex 7316 I asked about.

Cheers,

Shawn Prigmore

[Mr. Davis]

My 5998 Tung-sol Chatham came in the mail today. I'm listening to the Scorpions at the moment.  Its sounds quite good.  I've never heard my HD600 sound this good.  

I also have a CBS 6AS7G.  It sounds almost as good as the 5998.  It has a little bit more bass.

(https://lh6.googleusercontent.com/-hRgIfonKVME/Tk3XUbk7E_I/AAAAAAAAAow/uI-pjXKOqQI/s800/IMG_0271.JPG)

[TonyMc]

My 5998 Tung-sol Chatham came in the mail today. I'm listening to the Scorpions at the moment.  Its sounds quite good.  I've never heard my HD600 sound this good.  

I also have a CBS 6AS7G.  It sounds almost as good as the 5998.  It has a little bit more bass.

Nice. I just received a pair of RCA 6AS7G yesterday. Not a whole lot of difference in sound over the Tung-Sol 6080 that came with it, but it sure looks cool. Makes the Crack look like a beast.

[Laudanum]

My 5998 Tung-sol Chatham came in the mail today. I'm listening to the Scorpions at the moment.  Its sounds quite good.  I've never heard my HD600 sound this good.  

I also have a CBS 6AS7G.  It sounds almost as good as the 5998.  It has a little bit more bass.

I initially thought that the 6AS7 had a bit more bass than the 5998 as well (and it may).  But I wasnt so sure after listening for a while.  I heard subtleties in bass lines, for example, a little bit clearer with the 5998, skin attack on drums seems a little crisper and more defined.  Upper mids and treble seems a bit cleaner with a little more detail and treble maybe slightly more extended but smooth.  These were pretty subtle differences but noticeable.  With these differences in both the lower and upper ends of the frequency range I wasnt so sure that I was really hearing less bass but that it was a bit tighter. The 5998 has higher gain which is the most noticeable difference right off the bat.   But I did not play a wide range of music to compare and I didnt spend a huge amount of time analyzing the differences which isnt something Im good at anyway.  I'd rather just listen to the music and stick with a tube based on how the music "feels" rather than my actually thinking about how it sounds ... if that makes sense.
I was/am quite happy with the RCA 6AS7 and really wanted to try the 5998 more for my AKG K601's.  But the 601's reportedly have a long burn in and they really have changed from out of the box.  I put the 5998 aside to revisit after the 601's have had some good hours on them.  It will, in all probability, end up being the tube I use in Crack.  To me, it has a certain rightness to it's sound beyond the descriptions that I dont have the vocabulary to describe, assuming it's actually someting that could be put into words.  

[Mr. Davis]

I think your description of the 5998 is pretty darn good.

[Lar]

Just a quick question from a newbie, I have built the Crack with Speedball, was wondering if by swapping out to different tubes, would that alter my voltage check numbers?  Thanks.

[Doc B.]

Yes, different tubes can change the voltages on pins A1, A6, B1, B3, B4 and B6 somewhat.

[Lar]

Thanks Doc, i figured they might.

[williaty]

If the gain with the stock 6080 tube is around 15dB, what's the gain once you swap in a 5998?

[jrihs]

HI all! Regarding soviet era tubes...I was wondering what, if any difference is between the 6H13 and 6N13. I just got a 6H5 ... not a great tube in this application imho.

[Jim R.]

Nothing more than a translation issue -- h and n being alternate western designations for the same cyrillic letter.  Likewise b and v.  Source is a good friend with a Ph.D. in Russian Literature who works mostly as a translator.

In other words, it should bwe the same tube.

-- Jim